Transcriber’s Note


Subscripts are represented by bracketed numbers preceded by an
underscore: C_{10}H_{16}.




BY THE SAME AUTHOR.


Arithmetic of Electricity.

A Complete and Indispensable _vade mecum_ for amateur, student, and
electrical engineer.

  Fully Illustrated.      Price, $1.00.


Home Experiments in Science.

  252 Pages.      96 Illustrations.      Price, $1.50.




  RUBBER HAND STAMPS
  AND THE
  Manipulation of Rubber

  A PRACTICAL TREATISE ON THE MANUFACTURE OF INDIA RUBBER HAND
  STAMPS, SMALL ARTICLES OF INDIA RUBBER, THE HEKTOGRAPH,
  SPECIAL INKS, CEMENTS, AND ALLIED SUBJECTS

  BY
  T. O’CONOR SLOANE, A.M., E.M., PH.D.

  Author of
  “Home Experiments in Science,” “Arithmetic of Electricity,” etc.


  FULLY ILLUSTRATED


  NEW YORK
  NORMAN W. HENLEY & CO.
  150 NASSAU STREET
  1891




  COPYRIGHT, 1890, BY
  NORMAN W. HENLEY & CO.




PREFACE.


The present work hardly needs a preface. The object is to present in
the simplest form the subject of the manipulation of india rubber. To
mould and cure the mixed gum but few appliances are needed, and these
can be made at home. The articles produced are of more than ordinary
utility. These two facts give value to the art and furnish a _raison
d’être_ for this book. If its instructions do not prove practical it
will have missed its object.

For some reason the methods of moulding the material are not generally
known. Experiment has taught many the futility of attempting to
melt and cast it. While thus intractable by the usual methods, it
is the most plastic of materials when properly treated. Its power
of reproducing the finest details of a mould, of entering all the
intricacies and undercuttings of a design, cause one to feel a peculiar
pleasure in working with so responsive a material. It is not saying
too much to affirm that to some readers this book will disclose a long
hidden secret. To make it more generally useful it is written for such
readers, to meet the want of those knowing of the subject. It was felt
that in following this course, and in treating the subject from its
first steps, including the simplest as well as most advanced methods,
the book would appeal to a larger body of readers.

The allied subjects to which some chapters are devoted will be
acceptable to many readers. The hektograph is given in several
modifications. A substitute for rubber stamps which stands the severe
usage of the Post Office has very distinct merits, and the manufacture
is accordingly described in detail. Cements and inks embody many
special formulæ. In the last chapter interesting and practical notes
will be found.

For the use of certain cuts we are under obligations to the Buffalo
Dental Manufacturing Co., Messrs. E. & F. N. Spon & Co., and to Mr. L.
Spangenberg.




CONTENTS.


                                                                    PAGE
  CHAPTER I.

  THE SOURCES OF INDIA RUBBER AND ITS HISTORY.

    The Trees--The Sap--Caoutchouc--Early Uses by the
  Indians--First knowledge of it in Europe--Goodyear, Day, and
  Mackintosh                                                           9


  CHAPTER II.

  THE NATURAL HISTORY AND COLLECTION OF INDIA RUBBER.

    African, East Indian, Central and South American
  Gums--Different Methods of Collection and Coagulation               15


  CHAPTER III.

  PROPERTIES OF UNVULCANIZED AND VULCANIZED INDIA RUBBER.

    Properties of Unvulcanized Rubber; its Cohesion
  and importance of this property--Analysis of Sap and
  Caoutchouc--Effects of Heat and Cold--Distillation
  Products--Vulcanized Rubber, and its Properties                     24


  CHAPTER IV.

  THE MANUFACTURE OF MASTICATED, MIXED SHEET AND VULCANIZED
  INDIA RUBBER.

    Treatment by the Manufacturer--Washing and
  Sheeting--Masticating--Making Sheeting and
  Threads--Mixing--Curing--Coated Tissues                             35


  CHAPTER V.

  INDIA RUBBER STAMP MAKING.

    Mixed Sheet--Outlines of Moulding--Home-Made Vulcanizing
  Press--Further Simplifications of Same--Securing Accurate
  Parallelism of Platen and Bed--Distance Pieces--Wood vs.
  Iron as Material for Press--Use of Springs on the Home-Made
  Press--Metal Flask Clamps--Large Gas-Heated Vulcanizing
  Press--Preparing Type Model--The Matrix--Plaster of Paris and
  Dental Plaster as Substances for Matrices--Dextrine and Gum
  Arabic Solutions for Mixing Matrix--How Matrix is made--Shellac
  Solution for Matrix--Matrix Press and Spring-Chase--How to
  retard the Setting of Plaster of Paris--Oxychloride of Zinc
  Matrices--Talc Powder--Moulding and Curing the Stamp--Kerosene
  Heating Stove--Manipulation of Press--Degree of Heat--Simple
  Test of Curing--Time Required--Combined Matrix Making and
  Vulcanizing Apparatus--Chamber Vulcanizers--Object of Steam
  in Vulcanizers--Temperature Corresponding to Different Steam
  Pressures--Jacketed Vulcanizers--Gas Regulator--Flower
  Pot Vulcanizer--Fish Kettle Vulcanizer--Making Stamps
  without any Apparatus Whatever--Notes on Type, Quadrats and
  Spaces--Autograph Stamps                                            47


  CHAPTER VI.

  INDIA RUBBER TYPE MAKING.

    Movable Type Making--Simple Flask and Matrix--Precautions
  as to Quantity of Rubber--Moulding--Curing--Cutting Type
  Apart--Special Steel Moulds--Wooden Bodied Type                     73


  CHAPTER VII.

  THE MAKING OF STAMPS AND TYPE FROM VULCANIZED INDIA RUBBER.

    Ready Vulcanized Gum as Material for Stamps--Simplicity
  of the Process of Using It--Advantages and
  Disadvantages--Availability for Type                                77


  CHAPTER VIII.

  VARIOUS TYPE MATRICES FOR RUBBER STAMPS AND TYPES.

    Electrotype Matrices--Papier Maché--Flong Paste--Flong
  Matrices--Beating into Model--Drying and Baking--Struck-up
  Matrices--Chalk Plates                                              80


  CHAPTER IX.

  THE MAKING OF VARIOUS SMALL ARTICLES OF INDIA RUBBER.

    Suction Discs--Pencil Tips--Cane and Chair Leg
  Tips--Corks--Mats--Cord and Tubes--Bulbs and Hollow Toys            85


  CHAPTER X.

  THE MANIPULATION OF SHEET RUBBER GOODS.

    Sheet Rubber Articles--Toy Balloons--Uses of Sheet Rubber in
  the Laboratory                                                      94


  CHAPTER XI.

  VARIOUS VULCANIZING AND CURING PROCESSES.

    Liquid Curing Baths--Sulphur Bath--Haloids and Nitric
  Acid as Vulcanizers--Alkaline Sulphides--Sulphur Absorption
  Process--Parke’s Process                                            97


  CHAPTER XII.

  THE SOLUTION OF INDIA RUBBER.

    Mastication with Solvent--Peculiarities of
  the Process--Different Solvents and their
  Properties--Paraffin--Vulcanized Rubber Solution--Aqueous
  Solution                                                           103


  CHAPTER XIII.

  EBONITE, VULCANITE AND GUTTA-PERCHA.

    Ebonite and
  Vulcanite--Manufacture--Manipulation--Gutta-Percha and its
  Manipulation                                                       108


  CHAPTER XIV.

  GLUE OR COMPOSITION STAMPS.

    Substitute for Rubber Stamps--The United States Government
  Formula--Models and Moulds--Dating--Handles                        113


  CHAPTER XV.

  THE HEKTOGRAPH.

    How Made--The French Government Formula--Hektograph Sheets       121


  CHAPTER XVI.

  CEMENTS.

    Marine Glue, and other special Cements                           125


  CHAPTER XVII.

  INKS.

    Hektograph, Stencil and Marking Inks--White and Metallic Inks    129


  CHAPTER XVIII.

  MISCELLANEOUS.

    Preservation and Renovation of India Rubber--Burned Rubber
  for Artists--India Rubber Substitutes--General Notes of
  Interest                                                           134




RUBBER HAND STAMP MAKING AND THE MANIPULATION OF RUBBER.




CHAPTER I.

THE SOURCES OF INDIA RUBBER AND ITS HISTORY.


India rubber or caoutchouc is a very peculiar product, which is found
in and extracted from the juice of certain trees and shrubs. These are
quite numerous and are referred for the most part to the following
families: Euphorbiaceæd, Urticaceæd, Artocarpeæd, Asclepiadaceæd, and
Cinchonaceæd. It is evident that a considerable number of trees are
utilized in commerce for its production, and it is certain that it
exists, quite widely distributed, in many cases as a constituent of the
juice of plants not recognized as containing it.

When an india rubber tree is tapped, which is effected by making
incisions in the bark, the sap of the tree exudes. It is a milky
substance and is collected in various ways; it may be in vessels of
clay, in shells, or in other receptacles by the india rubber hunters.
If this substance is examined it is found to be of very remarkable
and characteristic constitution, resembling in its physical features
ordinary milk. It is composed of from fifty to ninety per cent. of
water, in which is suspended in microscopic globules, like the cream
in milk, the desired caoutchouc or india rubber. If the juice is left
to stand in vessels, like milk in a creamery, the globules rise to
the surface, and a cream of india rubber can be skimmed off from the
surface. If the juice is evaporated over a fire, the water escapes
and the india rubber remains. By dipping an article repeatedly in the
juice and drying it, a thick or thin coating of india rubber can be
developed. Before the modern methods for the manipulation of the gum
had been developed, and before the invention of vulcanization, this
method was adopted for the manufacture of shoes. The original “india
rubbers” for protection of the feet in wet weather were made in this
manner. A clay last was used, upon which the india rubber was deposited
as described. The clay last was then broken out and removed. Great
quantities of overshoes were thus made in South America, and many were
exported to Europe.

When caoutchouc has once been removed from this watery emulsion,
which for all practical purposes is a solution, it cannot be restored
to the former state of liquidity; it remains solid. It will absorb
a considerable quantity of water, but will not enter again into
the _quasi_ solution or combination. This property of permanent
coagulation, which interferes to a degree with its easy manipulation,
was early discovered. In the last century quantities of the natural
milk were exported to Europe to be used in what may be termed the
natural process of manufacture, because once solidified it could not be
redissolved, and because the manufacturers of those days had not the
present methods of dealing with the apparently intractable gum.

The natives of South America before the advent of Europeans, were
familiar with the treatment of the juice by evaporation just described
and used to make bottles, shoes and syringes of it for their own use.
The name _Siphonia_ applied to several species of rubber tree, and
_seringa_ (caoutchouc) and _seringari_ (caoutchouc gatherer) in Spanish
recall the old Indian syringes and tubes.

The gum is now collected for export in many parts of the world. South
and Central America are, as they have always been, the greatest
producers. Some is collected in Africa, Java and India. The best comes
from Para. However carefully treated a great difference is found in the
product from different countries. The Brazilian india rubber, known as
Para, from the port of shipment, ranks as the best in the market.

Its history as far as recorded, does not go back of the last century.
Le Condamine, who explored the Amazon River, sent from South America
in 1736 to the _Institute de France_, in Paris, the first sample of
india rubber ever seen in Europe. He accompanied the sample with a
communication. He said that the Indians of that country used the gum in
making several domestic objects of utility, such as vessels, bottles,
boots, waterproof clothing, etc. He stated that it was attacked and
to a certain extent dissolved by warm nut oil. In 1751 and 1768 other
samples were received through MM. Fresnau and Maequer, who sent them to
the Academy of Sciences, Paris, from Cayenne in Guiana.

Although from this period numerous experiments were tried with the new
substance little of importance was done with it for many years. Its
first use was to rub out pencil marks, whence it derived its name of
“india rubber.” As late as 1820 this continued to be its principal use.

An interesting reminiscence of its early history is given by Joseph
Priestley, the great English chemist of the last century, celebrated
as the discoverer of oxygen. In 1770 he mentioned the use of the gum
for erasing pencil marks, and speaks of its cost being three shillings,
about seventy cents, for “a cubical piece of about half an inch.”

As we have seen, its solubility was early studied. In 1761 Hérissant
added turpentine, ether and “huile de Dippel” to the list of solvents.
In 1793 its solubility was utilized in France by Besson, who made
waterproof cloth. In 1797 Johnson introduced for the same manufacture
a solution in mixed turpentine and alcohol.

The year 1820 is the beginning of the period of its modern use on a
more extended scale. Nadier developed the methods of cutting it into
sheets and threads and of weaving the latter. Mackintosh in 1823 began
the manufacture of waterproof cloth, using the solution of the gum in
coal tar naptha, which was caused to deposit by evaporation a layer of
the gum upon a piece of cloth which was covered by a second one. This
protected the wearer from the gummy and sticky coating of raw india
rubber. At the best the original Mackintoshes must have been very
disagreeable articles for wear.

In 1825 india rubber shoes of raw india rubber were imported from South
America and formed for a while an important article of commerce.

In 1839 Charles Goodyear, of Massachusetts, invented the art of
vulcanizing, or combining india rubber with sulphur. It was patented
on June 15, 1844, and covers only the manufacture of soft rubber.
Vulcanite or hard rubber (whalebone rubber) is disputed as to its
origin, its invention being assigned by some to Nelson Goodyear and by
others to Austin G. Day, of Connecticut. Goodyear however succeeded in
obtaining a patent on May 6, 1851. Day obtained a patent on August 10,
1858.

Vulcanization is the most important invention ever made in connection
with india rubber and may fairly rank as one of the greatest
discoveries of the present century. It is claimed by the English, an
inventor named Handcock being cited as the rival of Charles Goodyear.
The latter inventor had as an associate Nathaniel Hayward, who is
probably entitled to some of the credit.

By vulcanization india rubber loses susceptibility to heat and cold,
becomes non-adherent, and insoluble in almost all substances. It is
converted from a comparatively useless substance into one of wide
applicability.

The subject of india rubber is so interesting in its theoretical as
well as practical bearings that it seems impossible that those who
are workers in it should not feel an interest in its natural history.
For such readers the chapter on the natural history and collection of
india rubber has been written. As it is a product of widely separated
lands on both hemispheres, and as it is yielded by an immense number
of plants, it is impossible in the limits of a chapter to give a full
outline of its natural history.

The chapter in question is, therefore, with this apology, inserted
where it belongs, near the beginning of the book. Those who are
entirely practical may pass it over. There is no doubt that the few
minutes necessary for its perusal will be bestowed upon it by some.




CHAPTER II.

THE NATURAL HISTORY AND COLLECTION OF INDIA RUBBER.


African india rubber is mostly exported from the west coast. The belt
of country producing it extends nearly across the continent. Those
who are familiar with the india rubber plants of our conservatories
are apt to think of the gum as the product of trees, but in Africa
it is largely yielded by climbing plants of very numerous varieties,
belonging generally to the Landolphia species. It is collected by
the natives by careless or desultory methods, probably less advanced
than the ways followed by the South Americans. Possibly its marked
inferiority may be partly attributed to this. It is also supposed by
many that, were the gathering restricted to the vine producing the
best gum, better results would follow. As it is now all gums are mixed
indiscriminately. African gum is of very inferior quality.

The African india rubber vines grow often in dark moist ravines, where
no valuable product other than themselves could be cultivated. They
are entirely wild. The vines when cut exude an abundance of sap,
which differs from the South American product in its quickness of
coagulation. As it escapes from the wound it at once solidifies and
prevents the further escape of juice. The negroes are said to employ
the following highly original method of collecting it. They make long
gashes in the bark. As fast as the milky juice comes out they wipe it
off with their fingers and wipe these in turn on their arms, shoulders,
and body. In this way they form a thick covering of inspissated juice
or caoutchouc over the upper part of their body. This from time to
time is removed by peeling. It is then said to be cut up and boiled
in water. This is one account. According to others the natives remove
a large piece of bark, so that the juice runs out and is collected in
holes in the earth or on leaves. Wooden vessels are said to be used
elsewhere. Sometimes the juice is said to be collected upon the arms,
the dried caoutchouc coming off in the shape of tubes. A clew to the
inferiority of African india rubber is afforded by the statement that
too deep a cut liberates a gum which deteriorates the regular product
if it mixes with it. The drying of the gum is thought to have much to
do with its quality and it is highly probable that this affects the
African product. Some samples seem to be partly decomposed they are
so highly offensive in odor. The South American rubber is often dried
in thin layers, one over the other, by a smoky fire, which may have
an antiseptic effect upon the newly coagulated caoutchouc. No such
process as far as known is used in Africa.

The African india rubber appears under different names in commerce.
From the Congo region lumps of no particular shape called “knuckles”;
from Sierra Leone smooth lumps, “negro-heads,” and “balls” made up
of small scrap; from the Portuguese ports “thimbles,” “nuts,” and
“negro-heads;” from the gaboon “tongues;” and from Liberia “balls”
are received. It is all characterized by great adhesiveness and low
elasticity.

From Assam, Java, Penang, and Rangoon there is considerable gum
exported. It is supposed to be the product of trees of the _ficus_
species, in all these places, as it is known to be in Java and Assam.
In the latter place rigid restrictions are imposed as far as possible
upon the gathering. In the case of wild trees scattered through the
forest the carrying out of these restrictions is not practicable. The
trees are cut with knives in long incisions through the bark and the
juice is collected in holes dug in the ground, or often in leaves
wrapped up into a conical form, somewhat as grocers form their wrapping
paper into cornucopia shape for holding sugar, etc.

It has seemed reasonably certain that the india rubber producing plants
might be cultivated with profit, and it is as certainly to be feared
that without such cultivation they will become extinct. Efforts have
been made in the direction of raising them artificially but without
much success. In Assam numerous experiments have been made to propagate
the india rubber bearing _ficus_ tree.

A good instance of the ill effects of carelessness in the original
gathering of the crop is afforded by the Bornese collectors. The source
of Borneo india rubber is a variety of creepers. These are cut down and
divided into short sections from a few inches to a yard in length. The
sap oozes out from the ends. To accelerate its escape the pieces are
sometimes heated at one end. It is coagulated by salt water. Sometimes
a salt called _nipa_ salt, obtained by burning a certain plant (_nipa
fruticans_), is used for the purpose. In either case it is coagulated
into rough balls and masses. These masses are heavily charged with the
salt water, often containing as much as fifty per cent., and rarely
much less than twenty per cent.

[Illustration: TREE FELLED FOR COLLECTION OF INDIA RUBBER.]

Central America and Panama are great producers of the gum. In Panama
the custom of felling the trees is often adopted. In this case
grooves are cut around the prostrate trunk, and under each groove as
the trunk lies on the ground a vessel is placed to collect the sap.
Its coagulation is often effected by leaving it for a couple of weeks
standing at rest in a hole, excavated on the surface of the ground,
and covered over with leaves. The caoutchouc separates under these
conditions. A quicker method, but one yielding an inferior product,
is obtained by adding to the fresh juice some bruised leaves of a
plant (_ipomæa bona nox_) which acts something like acid upon milk,
in separating the desired solid matter or caoutchouc. A jelly like
accretion saturated with blackish water is thus obtained. By working
it together a blackish liquid is caused to escape, and comparatively
pure gum is gradually obtained. As much as one hundred pounds of india
rubber may be obtained from a single tree where this destructive system
is employed. Further north, where a better counsel has prevailed, the
trees are only tapped, and the india rubber hunter is satisfied if from
a tree eighteen inches in diameter he obtains twenty gallons of sap,
giving fifty pounds of gum. Even where tapping is done the tree is
often destroyed by carelessness or ignorance.

Two systems are followed in Nicaragua. The operator ascends by a ladder
if he has one, or in any case climbs as high as he well can and begins
to make a long incision. Sometimes he carries one long straight cut
clear down to the ground. This is made the starting point for a number
of side cuts, short, and running diagonally into it. This is also one
of the Brazilian methods. The Nicaraguan sometimes also makes two
spiral incisions, one right-handed and the other left-handed, crossing
each other as they descend so as to divide the surface of the tree
into roughly outlined diamonds. In either case the juice flows down
to an iron spout, placed at the bottom of the tree, which spout leads
to an iron pail. The milk is gathered and passed through a sieve, and
coagulated in barrels by the _ipomæa_ plant as before mentioned. This
gives three grades of rubber. The bulk is obtained from the barrels and
is called often _méros_; the small lump which forms in the spout is
rolled into a ball and called _cabezza_; the dried strips pulled out of
the cuts is of very good quality and is called _bola_ or _burucha_.

From Brazil is exported the famous Para india rubber. This is of very
high quality, and is greatly esteemed by all manufacturers. No process
can make a poor gum give a really good product. The system of gathering
it varies. Sometimes the tree is cut into by gashes from an axe, such
gashes extending in a row all around the trunk. Under each gash a small
clay cup is luted fast with some fresh mixed clay. These collect from
a tablespoonful of juice upward, which is collected, and the cups are
removed on the same day. The next day a second row of cuts is made
below the others, and the same process is repeated. This is continued
until from a point as high as a man can reach, down to the ground the
tree is full of cuts. Sometimes a gutter of clay is found partly around
the trunk with gashes above it. In other cases a vine is secured around
the tree and a collecting gutter is worked with it for a basis.

[Illustration: TREE TAPPED FOR INDIA RUBBER.]

The juice is coagulated in a smoky fire. A bottomless jar is placed
over the fire and some palm nuts are mixed with the fuel. The mould,
which is often a canoe paddle, is smeared with clay to prevent adhesion
and is then heated. A cup of juice is poured over it, and after the
excess has dropped off it is moved about rapidly over the smoke and
hot air which ascends from the mouth of the jar. This series of
operations is repeated until the coating is quite thick; it may be as
much as five inches. After solidifying over night it is cut open and
the paddle or mould is removed. After a few days drying it is sent to
market. With all the heating, during which it sweats profusely, it
still retains fifteen per cent. of water.

[Illustration: INDIAN DRYING AND SMOKING INDIA RUBBER.]

India rubber sap may be coagulated by an aqueous solution of alum. The
process has been tried in Brazil, and is used to a considerable extent
in Pernambuco. It was proposed by an investigator named _Strauss_, and
the process is still called by his name. One objection is that it gives
a very wet product, and apparently one of inferior value to the smoked
gum.

The feeling that india rubber suffers in the gathering has been so
much felt that it has been recently suggested that if possible the
uncoagulated juice should be exported to Europe there to be worked up
from the beginning.




CHAPTER III.

PROPERTIES OF UNVULCANIZED AND VULCANIZED INDIA RUBBER.


There are two broad divisions to which all varieties of india rubber
can be assigned--unvulcanized and vulcanized rubber. Speaking with
a certain amount of license it may be said that more properties
characterize the former than the latter. The vulcanized article is very
slightly affected by ordinary changes of temperature, cannot to any
considerable extent be changed by heat short of absolute destruction or
decomposition, cannot be united or moulded except in simple forms, is
highly elastic, and is insoluble in almost every solvent for ordinary
caoutchouc.

Unvulcanized caoutchouc possesses very interesting and peculiar
properties. The first part of the present chapter is devoted to this
substance. Those who have never seen the crude gum as imported are
familiar with the article almost pure in the form of sheet rubber and
black rubber articles generally. These are of nearly pure caoutchouc,
though recently the tendency is to vulcanize them to a considerable
degree.

A piece of pure gum containing no combined sulphur, iodine, or other
vulcanizing constituent will be found to exhibit a very striking
peculiarity. Two freshly cut surfaces when placed in contact will
adhere. This is not in consequence of any viscous or sticky coating.
When india rubber is cut the surface is perfectly dry and non-adherent
except to itself.

The writer once had this property of adhesion brought strongly to
his attention. In some analytical investigations of coal gas he had
proposed to use finely divided india rubber as an absorbent of sulphur.
This constituent it absorbs from gas, and it seemed that a basis for a
quantitative determination of sulphur might be found in such property.
Accordingly some raw india rubber was procured and with some trouble
was cut up into little pieces which were put into a bottle. A day or
two afterwards the pieces united wherever they were in contact, and an
irregular cavernous lump was the result. This involved no melting or
softening or change of shape. Each little piece was there intact and
distinct but firmly attached to its neighbors.

The analogy of this action is seen in lead. Two fresh surfaces brought
together, preferably with a twisting or wrenching pressure, adhere
quite firmly. The adherence of india rubber and of lead each to
itself is often exhibited by physical lecturers as an illustration of
cohesion. The cohesion of india rubber is however far more perfect than
that of lead, probably because of its comparatively great resistance
to oxidation, and because, owing to its elasticity larger areas can
be brought in contact. Comparatively great though this resistance to
oxidation is, oxygen, especially in the allotropic modification known
as ozone, may act quite powerfully on the gum. Sunlight also can affect
it injuriously.

A more familiar illustration of the uniting of two pieces of the
same material is seen in the welding of iron. The blacksmith heats
two pieces of iron until they are nearly white hot and are pasty in
consistency. On placing them in contact and hammering to force them
together they unite so firmly as to be practically one. It is necessary
that the surfaces of clean metal should be brought together. If the
pressure induced by the hammering is insufficient to bring this about,
a flux is added which dissolves the oxide and causes the metal to come
in contact with metal and to weld. The analogy with india rubber in its
cohesive action is evident. Surfaces long exposed or which are dusty do
not cohere. The relegation of ice is similar in effect.

The cohesion of india rubber is important and should be thoroughly
appreciated. It is not saying too much to assert that the entire
treatment of the raw gum depends upon this interesting property. The
great lumps of gum are torn to pieces and washed free from gravel and
dirt without going to powder, because owing to their elasticity they
yield and as fast as torn apart the pieces tend to reunite. Again
india rubber is mixed with pigments and vulcanizing reagents by a
method practically one of grinding or masticating, but the material
while it changes its shape, and by the admixture of the various
ingredients becomes less strong or easier torn, still remains intact,
as it welds together or coheres as fast as disintegrated.

As regards its chemical constitution the sap of a Para rubber tree has
been analyzed with the following general results: (Faraday).

  Caoutchouc                                        30.70
  Albuminous, extractive, and saline matter, etc.   12.93
  Water                                             56.37
                                                   ------
                                                   100.00

Its specific gravity is 1.012.

Caoutchouc itself or raw india rubber is a mixture of several
hydrocarbons of the following composition in general:

  Carbon     87.5
  Hydrogen   12.5
            -----
            100.0

Its specific gravity is from .912 to .942.

The hydrocarbons composing it are isomeric or polymeric with
turpentine. This fact brings it well within the range of familiar
vegetable products. As will be seen the products of its distillation
fall among the same polymers and isomers.

When pure it is nearly colorless, the dark color being due to
impurities. In thin sheets it is almost or quite transparent. It burns
readily, and with a very luminous, smoky flame, as might have been
anticipated from its composition. The action of heat and cold on it is
dependent on the degree of the temperature. At ordinary temperature
it is elastic and firm. It can be stretched and will return almost
to its original size when released from tension. Yet the return
to its shape is so liable to be incomplete, especially after long
sustained stretching, that pure unvulcanized india rubber is considered
imperfectly elastic.

Any elasticity it possesses is principally elasticity of shape as
distinguished from elasticity of volume. In other words when pressed or
stretched it may change shape to a great extent but hardly change its
volume at all. A cube of 2½ inches under a weight of 200 tons lost 1-10
of its volume only. This is largely due to the fact that it represents
an approximately solid body, or one destitute of considerable physical
pores. Solids and liquids are very slightly compressible. Whatever
degree of compressibility caoutchouc possesses is due principally to
its minute pores.

If the temperature is reduced to the freezing point of water a piece
of raw india rubber becomes rigid and stiff. On application of heat
it returns to its former pliable condition. The same return to
flexibility may be brought about by stretching it mechanically. This
may be rather a fallacy. Stretching india rubber warms it, so that in
this mechanically imparted rise of temperature we may find at least a
probable cause of the softening.

If the temperature is raised several effects are produced, according
to circumstances. A piece which has been stretched and held stretched,
has its tension increased by a degree of heat considerably less than
that of boiling water. Some offer the theory that it contains air
enclosed in its pores which, expanding, produces this effect. As the
boiling point is reached the material softens and becomes somewhat
plastic, so that it can be moulded into shape to a considerable extent
and stretched to threads of great fineness. Its elasticity also
disappears as the heat is maintained. These effects increase in extent
up to a heat of 248° F. (120° C.). The return to its original state is
not immediate however. Some time is required before the reduction of
temperature will have full effect.

If now a still higher degree of heat is applied, 392° F. (200° C.) the
india rubber softens to a viscous body, or melts. From this state it
cannot be restored. It remains permanently “burned” or melted whatever
is done to it. Some attempt at hardening may be made by the use of
vulcanizing chemicals, but the result will be very imperfect.

A further increase of heat brings about a destructive distillation.
India rubber treated in a retort to a heat exceeding 400° F. (204° C.)
evolves volatile hydrocarbons of oily consistency, and it distills
almost completely, a small residue of gummy matter or of coke if the
final heat has been pushed far enough being left. The distillate is
called caoutchoucin. According to Mr. Greville Williams it consists of
two polymeric hydrocarbons: one, caoutchin C_{10}H_{16}, boiling point
340° F. (171° C.); the other, isoprene C_{5}H_{8} (in formula equal to
one-half of caoutchin), boiling point 99° F. (37° C.). The mixture has
a strong naptha-like odor and has won considerable reputation as being
the best solvent for india rubber. How far it deserves its reputation
is a matter open to discussion.

The solution of india rubber like its fusion is a vexed point. There is
little question that it can be dissolved by proper treatment. Usually
naptha, carbon disulphide or benzole are used as solvents, the choice
being guided by motives of cheapness and efficiency.

It is worthy of remark that the formula given for caoutchoucin is
the same as that of the principal constituent of oil of turpentine,
and that the latter is often recommended as a solvent. Turpentine is
slightly more volatile than caoutchoucin, its boiling point being 322°
F. (161° C.) Other hydrocarbons have been recognized in the distillate
by Bouchardat, Himly and G. Williams, varying in boiling point from 32°
F. (0° C.) to 599° F. (315° C.), and in specific gravity from 0.630 to
0.921.

Although it has been spoken of as approximately solid it does possess
microscopic pores, to which its limited amount of elasticity of volume
is mostly due. Thus it is found to absorb water, in which it is quite
insoluble. As it does this it acts like a dry sponge and increases in
volume a little, owing to dilation of these minute pores. The water
absorbed may be as much as 18.7 to 26.4 per cent. with an increase of
volume of the gum of 15/1000 to 16/1000. When it has once absorbed
water it is very hard to get rid of it. Although the minute surface
orifices communicate with the entire system of capillary vessels and
pores, the surface pores on drying contract and seal up the absorbed
water within the mass. This is a clew to the impracticability of
the gatherer shipping dry rubber, and to the great difficulty the
manufacturer experiences in drying his washed and sheeted stock before
working it up by masticating or mixing and curing.

By proper manipulation caoutchouc may be made inelastic. This can be
done by the freezing process or by keeping it stretched for two or
three weeks. In this way threads can be made to extend and to remain
extended to seven or eight times their original length. They can then
be woven into a fabric. On gentle heating their original elasticity
reappears and they contract. In this way fluted braids can be made
which will have a high capacity for stretching.

The solution of caoutchouc is difficult often to bring about. We have
seen that in water it swells a little without dissolving. In benzole
it does the same, but swells to a greater extent, to 125 times its
original volume or even more. Some authorities (_Watts_) go so far
as to assert that no solvent completely dissolves it. Acting on it
repeatedly with benzole or other solvent and taking care not to break
up the swelled mass, from 49 to 60 per cent. of soluble matter can
be extracted. On evaporation this is deposited as a ductile adherent
film. The swelled up residue which remains undissolved is assumed to be
the constituent giving strength and elasticity, and is only sparingly
soluble. If the gum is masticated or kneaded at the temperature of
boiling water a change occurs not well understood, by which its
solubility is greatly increased. As solvents many liquids have been
named. Oil of turpentine, caoutchoucin, coal-tar, naptha, benzole,
petroleum-naptha, coal-tar-naptha, anhydrous ether, many essential
oils, chloroform, bisulphide of carbon, pure, or mixed with seven
or eight per cent. of alcohol, are among the solvents recommended.
A mixture of fifty parts of benzole and seventy parts of rectified
turpentine has been given as a solvent for twenty-six parts of the gum.
Mastication before or after immersion in the solvent is to be advised.
More will be said on this subject in a succeeding chapter.

Vulcanized india rubber is unaffected by changes of temperature within
ordinary range. It softens a little on heating. Even hard vulcanite
when heated can be bent and will retain the bend on cooling. It is
exceedingly elastic with elasticity of shape but far less compressible
as regards absolute change of volume than the raw gum. It melts at
392° F. (200° C.) It cannot be made to cohere, and no cement has yet
been discovered that will satisfactorily unite two surfaces. It is
unaffected by light, by ordinary acids and rubber solvents. In contact
with the latter solvents it swells sometimes to nine times its original
volume, but on heating returns to its original volume and shape. Of
water it will absorb no more than four per cent. and often much less.
If it is maintained at a high temperature 266° to 302° F. (130° to 150°
C.) for a long time it gradually loses its flexibility, especially
if in contact with metals. Often the escape of sulphuretted hydrogen
may be observed under these conditions. A small admixture of coal tar
operates to prevent this action.

Its composition and specific gravity vary widely as the most varied
mixtures are added by the manufacturer. Its relation of carbon to
hydrogen is unaffected by the mixtures added. While it may contain
twenty per cent. or more of sulphur it is believed that but a very
small quantity is combined with it, although the excess of sulphur
or some equivalent, such as sulphide of antimony is essential to
vulcanization. The combined sulphur is from one to two per cent. Some
or all of the excess of sulphur is mechanically retained, and as the
rubber in ordinary use is worked about, keeps escaping and forms a
whitish dust upon the surface. By treatment with alkali some of the
excess of sulphur can be removed when the rubber acquires the power of
absorbing a little more water, up to six and four-tenths per cent.

Boiling oil of turpentine is given as its solvent.




CHAPTER IV.

THE MANUFACTURE OF MASTICATED, MIXED SHEET, AND VULCANIZED INDIA RUBBER.


The manufacture of india rubber relates to the production of two
principal products. One is masticated unvulcanized sheet and thread
rubber; the other is unmasticated mixed and cured rubber, otherwise
vulcanized rubber. For the purposes of the rubber-stamp maker an
intermediate product is required, namely, unmasticated mixed sheet
which is uncured. This is really incompletely vulcanized india rubber.

It will be evident from the description to come that it is not
advisable for any one without considerable apparatus to attempt to
clean and to wash (“to sheet”), to masticate, or to mix india rubber.
These operations are best accomplished in the factories. The partially
vulcanized (“mixed sheet”) or the pure masticated article are regular
articles of commerce. Yet a full insight into the manipulation of india
rubber can only be obtained by understanding its treatment from the gum
up to the two separate lines of products we have indicated.

A third type of product is coated tissue, such as Mackintosh. This
really is a sequence of one of the other two processes and a few words
will be said of it in concluding the chapter.

As the caoutchouc is received by the manufacturer it appears an
utterly intractable mass. It occurs in lumps of every size, varying in
color and odor, and very tough but elastic. In virtue however of the
properties already described, its power of cohering when cut, and its
softening when heated, it becomes amenable to treatment.

It is to some extent received in such assorted condition as to secure
even grades, and then each grade may be washed by itself. It is
thrown into water which is in many cases kept at the boiling point by
steam-heat and left there for some hours. It absorbs some water and
also softens. Some gum is so soft that it will not stand hot water. For
such the water is kept cold. The purer gum floats; such pieces as have
stones, dirt, iron, etc. in them, perhaps placed there purposely from
fraudulent motives, sink and can be picked out for separate treatment.

The lumps are next cut up. A revolving circular knife driven by power
is often used, and sometimes an ordinary knife is adopted. At this part
of the operation there is frequently need for sorting, as the grades
received may have inferior pieces mixed with the good. The cutting is
mainly to secure good grading, and to remove concealed impurities. The
gum then goes to the washing rollers, called the washer and sheeter.
(See cut, p. 37.)

[Illustration: WASHER AND SHEETER.]

These are heavy corrugated rolls made very short, 9–18 inches in
length, to prevent springing. They are grooved or corrugated and have a
screw adjustment for regulating their distance apart. They are geared
together so as to work in corresponding directions, like a clothes
wringer or a rolling mill of any kind. The pieces of gum are fed into
the rolls and are drawn between and through them. The friction tends
to heat the gum. To prevent this and also to effect the washing, a
supply of water, either hot or cold, is kept playing upon the mass.
This dissolves out all soluble matter and washes away mechanically the
chips, dirt, etc. which may be present. The whole operation is one of
main force. The caoutchouc is torn and distended and delivered as a
rough perforated sheet. It is passed repeatedly through the machine,
the rollers being gradually brought closer together, or else different
sets of rolls are used, set to different degrees of fineness. The
wash water passes through a screen which catches any small detached
fragments of gum.

Other types of machines have been introduced; the above is a
representative form.

The rough sheets must now be perfectly dried, as water impairs the
final product. This is done in drying rooms by steam heat, generally,
at a temperature of about 90° F. (32° C.) The windows, if there are
any, are painted to exclude sunlight, which operates to deteriorate raw
gum. When absolutely dry the caoutchouc is removed and stacked away for
use.

[Illustration: MASTICATING MACHINE.]

To prepare pure gum for the manufacture of sheet rubber and as a
starting point for many other preparations, the india rubber is
“masticated” in special apparatus. The machine consists of a fixed
cylinder within which is a corrugated roller set eccentrically and
rotated by power. The perfectly dry sheets in the masticator are
pressed and rolled and ground and produce a mass of even consistency.
Here the welding or cohering action again appears in its fullest
development. The perfect dryness of the mass enables it to keep
reuniting as fast as divided. The action is assisted by the heat
generated, which is not inconsiderable. Sometimes the caoutchouc is
warmed before introduction, and sometimes the roller is heated by
passing steam through it.

[Illustration: MASTICATING MACHINE.]

The masticating machine the French picturesquely term the wolf (_loup_)
or devil (_diable_). It is given from sixty to one hundred turns a
minute, and a machine large enough to treat fifty pounds of gum in a
charge, requires five horse-power to drive it. In it the sheeted gum is
ultimately brought to the state of a perfectly homogeneous dark brown
translucent mass.

The masticated rubber is peculiarly amenable to mechanical and chemical
treatment. It can be shaped by heat and pressure, and it is the most
soluble form and is used for making cement and solution, and is moulded
into blocks for the manufacture of sheet and thread rubber. In the
process neutral body pigments, such as oxide of zinc, or soluble
transparent ones, such as alkanine may be introduced; easily decomposed
matter cannot be incorporated on account of the heat.

In all these machines special provision is made to prevent any oil from
getting into the gum. There is no greater enemy to india rubber than
oil or fats of any description. The flanges in the masticator that roll
just inside the bearing are for this purpose.

Sheet rubber is made from the blocks of masticated gum by slicing. A
machine is used for the purpose which carries a knife which works back
and forth in the direction of its length at high speed, making two
thousand cuts a minute. The knife is kept wet by a stream of water,
and about sixty cuts are made per inch. In many articles made from
this sheet the marks of the cuts can be seen as a fine ribbing. The
appearance is familiar to many readers.

The sheet is often cut from rectangular blocks, but cylindrical blocks
are also used. The latter are rotated in front of the knife edge and a
long, continuous sheet can thus be obtained.

The sheet rubber can be cut into threads on webbing and braid. Everyone
has noticed that these threads are usually square. The method of
preparation accounts for it. Vulcanized sheet is now almost universally
used for threads.

Round threads however can be made by forcing softened or partly
dissolved gum through a die.

It is from unvulcanized masticated sheet that toy balloons, tobacco
pouches, etc., are made. It is the starting point for india rubber
bands. For the usual form of the latter article the sheet is cemented
into a long tube which is afterwards cut transversely, giving bands
of any desired width. To make any of these articles satisfactory
vulcanization is imperative. Unvulcanized rubber for many years was
used, but it is now completely displaced by the vulcanized product.
Sheet rubber is made as above; is vulcanized by some of the absorption
processes described in the chapter on vulcanization.

We now come to the second product: regularly mixed and cured rubber.
Its starting point is the washed india rubber from the washer and
sheeter.

We have seen that the pure gum or caoutchouc is very sensitive to
changes of temperature. At the freezing point of water it is hard and
rigid, and at the boiling point is like putty in consistency. There
are several substances which can be made to combine with the gum and
which remove from it this susceptibility to change of temperature. The
process of effecting this combination is called vulcanization, and the
product is called vulcanized india rubber. Sulphur is the agent most
generally employed.

[Illustration: MAKING MIXED RUBBER.]

In the factory the normal vulcanization is carried out in two steps,
mixing and curing. The washed sheet india rubber which has not been
masticated and which must be perfectly dry is the starting point, and
the mixing rolls shown in the cuts are the mechanism for carrying out
the first step. These are a pair of powerful rollers which are geared
so as to work like ordinary rolls, except that one revolves about
three times as fast as the other. They are heated by steam, which is
introduced inside of them. The sheet is first passed through them a few
times to secure its softness, and then the operative begins to sprinkle
sulphur upon it as it enters the rolls. This is continued, the rubber
passing and repassing until perfect incorporation is secured. About ten
per cent. of sulphur is added, and a workman can take care of thirty
pounds at a time.

This material is incompletely vulcanized. It is in its present
condition very amenable to heat and is ready for any moulding process.
Generally it is rolled out or “calendered” into sheets of different
thickness from which articles are made in moulds by curing.

These sheets are of especial interest to the reader as they are the
material from which most small articles are made, including rubber
stamps.

This rolling of the mixed india rubber into sheets of definite
thickness is done by special calendering rolls. The product is termed
“mixed sheet.”

In the mixing rolls the incorporation of other material is often
brought about. Zinc white, lead sulphide, antimony sulphide, chalk,
clay, talc, barium sulphate, plaster of paris, zinc sulphide, lead
sulphate, white lead, oxides of lead, magnesia, silica, form a list
of ordinary mixing ingredients. These lower the cost of the finished
material and are often serious adulterants. For some cases the addition
if not carried too far is not injurious, or even may be beneficial. A
proper admixture renders the gum more easily moulded and treated in the
shaping processes.

[Illustration: MIXING ROLLS.]

The next step in the vulcanizing process is the heating of the mass,
which step is called “curing.” Up to a temperature in the neighborhood
of that of boiling water the mixed rubber can be heated without change
except as it is softened. But if the heat is increased it begins to
get a little more elastic and less doughy, and eventually becomes
“cured” or vulcanized. The temperature for vulcanization is about 284°
F. (140° C.). The word “about” is used advisedly, for it is not only a
question of heat but of time of exposure. After vulcanizing, including
the curing, india rubber cannot be moulded to any great extent. In the
manufacturing process, therefore, it is before curing placed in the
moulds, heated, shaped by pressure, and by exposure to a higher heat
in a steam oven called a vulcanizer, is at once cured.

To prevent adherence to the moulds they are dusted over with ground
soapstone, and the rubber itself is often thus coated.

The methods of vulcanization and curing, which may be of special use to
the reader, are given in the chapters devoted to that subject (chapter
XI.), and in the one devoted to rubber stamps.

Hard rubber, termed ebonite when black, and vulcanite when of other
colors, is simply vulcanized rubber containing a large percentage of
sulphur added in the mixing process.

The manufacture of coated tissues is effected in several ways. The
following is a typical process. A mixture of one part washed and
sheeted india rubber with one part zinc white, one fourth part sulphur,
and about one third part naptha is mixed into a dough-like mass and is
spread upon the cloth by machinery. The latter is simple. It consists
of a bare board arranged to move under a scraping bar. The cloth is
placed on the board and carried under the bar. The coating mixture is
fed on one side of the bar upon the surface of the cloth. As it passes
under, a regulated amount, according to the set of the bar, adheres. It
is then dried by steam heat and recoated, until ordinarily six coats,
each about one one-hundredth of an inch in thickness, have been given.
Three coats are given in each direction with intermediate drying. The
fabric is then cured by heat in vulcanizers.

Sometimes the sulphur is omitted from the mixture and cold curing, as
described later, is adopted. When the goods are made up the seams are
secured with rubber cement, a thick solution of masticated gum. Such
seams have to be vulcanized.

Sometimes two such fabrics before curing or vulcanization, are placed
face to face and allowed to adhere and are then cured or vulcanized.

Enough has been said in this outline of the manufacturer’s treatment
of india rubber to show that the first treatment requires machinery.
Very little can be done with mortar and pestle, although in making up
solution these simple instrumentalities are available. As a starting
point for making small articles masticated sheet rubber and mixed
sheet rubber are the staple materials. The preceding steps are best
accomplished in the factory.




CHAPTER V.

INDIA RUBBER STAMP MAKING.


We have seen that india rubber cannot be cast in moulds. Except in
special cases deposition from solution is not available. It has to
be shaped by a combination of heat and pressure. When gently heated
it softens and can be pressed in a mould. As it cools it retains the
shape thus given and is moulded. This applies to all unvulcanized india
rubber. If mixed rubber is moulded and heated to a higher temperature
without removal from the mould the curing process is brought about and
the rubber may be not only moulded but cured and the product is moulded
vulcanized india rubber. The mixed sheet whose manufacture is described
in chapter IV. (page 42) is the starting point in rubber stamp making.
It is made for this purpose by the manufacturers.

When the material is examined it looks like ordinary white india
rubber, being firm in texture and quite strong. On heating to 280° F.
to 290° F. (137° C. to 143° C.) it begins to become “cured,” and if in
a thin sheet one to ten minutes are sufficient for the process. As the
heat is applied the india rubber first softens and becomes much like
putty. It can now be pressed through the smallest orifice and will fill
up the finest details of anything it is pressed against. It is at this
point that pressure must be applied to drive it into the interstices of
the mould.

As the heat continues it begins to lose its doughy or putty-like
consistency. This marks the reaction of the vulcanizing materials.
They gradually combine with and change the nature of the caoutchouc.
The rubber while still quite soft is elastic. If pressed by the point
of a knife it yields, but springs back to its shape when released from
pressure. The india rubber is vulcanized.

On removal from the mould it will be found to reproduce its smallest
detail. The color and appearance have not changed much, but its nature
and properties are now those of vulcanized rubber. It is unaffected by
heat or cold within ordinary ranges of temperature, and if the india
rubber is of good quality and made by a proper formula it will last for
years.

[Illustration: SIMPLE VULCANIZING PRESS FOR RUBBER STAMPS.]

The first thing to be described is the mould, which includes the
arrangements for pressing the sheet of india rubber while heated. A
small press is needed for this purpose. It may be of the simplest
description, and as an example of a home-made but perfectly efficient
one the illustration may be referred to. The base of the press is a
piece of iron, if heat is to be directly employed. Where a chamber
vulcanizer is used both base and platen may be of wood. But from every
point of view iron is the best. It lasts forever, admits of direct
heating, and does not split, warp, or char. Through two holes drilled
near its opposite sides two ordinary bolts are thrust. It is best to
use flat headed bolts, and to countersink a recess for the heads in
order to keep the bottom level. The heads may need to be filed off
so as to reduce their thickness, in order to secure this object. The
bolts may be soldered in place. One thing should be carefully watched
for--the bolts should be set true so as to rise vertically from the
plane of the base.

The platen is best made of iron, cut of the shape shown. This is an
excellent disposition of the screw-bolt slots, as by swinging the
right end of the platen back it can be taken off without removing the
nuts and lifting it over the ends of the screws. Besides the two nuts
fitting the thread of the screws it is well to have half a dozen extra
ones larger than the others, which will slip easily over the bolts,
so as to act as washers. The object of these is to adapt the press to
objects of different thickness. The thread upon an ordinary bolt does
not extend clear to the head, but by slipping on some loose nuts the
plates can be forced together if desired.

This press can be simplified. Both base and platen can be made of wood,
the platen being simply bored for the bolts, and the latter driven
tightly through the holes in the base so as to retain their place.
Even this can be improved on as regards simplicity. Two blocks of wood
screwed together by two or more long wood screws may be made to do
efficient work.

One trouble is apparent with all these devices, and that is the want of
parallelism of the opposed planes. The base and platen may be true and
parallel or they may not. Perhaps the simplest way of securing this is
the best. It consists in placing across the base two distance pieces,
which may be slips of wood. These must have perfectly parallel faces.
As the press is screwed up they will be gripped between the platen and
base and will not only ensure their parallelism but will keep them at
an exact distance apart. Such distance pieces are shown in the same
cut. Pieces of printers’ “furniture,” spaces, or “quads,” may be used
for this purpose. They should not be fastened in place if there is need
to adapt the press to more than one thickness of material and matrix.

The above described apparatus is a vulcanizing press. A further
improvement in it may be effected by the use of spring pressure. Two
strong spiral springs may be dropped over the bolts, the nuts being
screwed on above them, or a powerful spring of flat brass or steel
ribband bent into the shape of a shallow letter V may intervene between
nuts and platen, the centre of the bend bearing against the centre of
the platen.

As regards the strength of the springs there is this to be said. The
distance pieces will prevent a spring that would ordinarily be too
powerful from doing any harm. Such distance pieces should be used, as
the springs must be based upon giving a pressure of many pounds per
square inch of surface to be acted on. They should have a range of an
eighth of an inch or more. The greater the range the more evenly will
they work.

The next cut shows an excellent little screw press, that is made for
the purpose of pressing vulcanizing flasks. This is so simple that it
will suggest to the mechanical reader how he can make a single-screw
press, which is by far the most convenient to use. In the stationery
stores very small model cast iron copying presses designed for use as
paper weights are sold. They are excellent for a limited amount of
small sized work.

[Illustration: VULCANIZING FLASK CLAMP.]

A large sized gas heated press, such as made for the purpose of
manufacturing rubber stamps, is shown in the next cut, p. 53. Its
construction is obvious. It is termed by the trade a vulcanizer. Its
manipulation will be given further on.

Type are generally the object to be copied. These are best set up with
high quads and spaces. Naturally rather a large type is chosen, with
extra wide spaces between the letters. Some advise rubbing the type
faces full of hard soap, afterwards brushing off the face, leaving the
hollows filled. Sometimes wax is recommended for the same purpose.
This prevents the plaster of the matrix entering so deeply into the
cavities of the letters.

[Illustration: GAS-HEATED STAMP VULCANIZER.]

The type forming the model to be reproduced, is locked in a frame. Two
pieces of printers’ furniture or other wooden strips screwed together
by wood screws at their ends will answer for a locking frame for small
inscriptions.

The model to be copied need not be type, but any desired relief may be
used, such as an electrotype, a stereotype, an engraving or another
rubber stamp. In any case it is to be placed upon a flat surface, best
an “imposing stone” or piece of marble, with the inscription upwards.
On each side of it distance pieces reaching about one-eighth inch above
its upper surface are to be placed.

The next shaping appliance is the matrix or mould, or reverse of the
model which is to be copied. This in the case of rubber stamps is
properly called the matrix. Those who have witnessed the stereotyping
of a large daily newspaper have seen the matrices of the type made of
paper and paste, the whole mixture being termed “flong.” Such a matrix
is required for rubber type, but paper is rather too susceptible to
heat although good work can be done with it. It also does not enter
as deeply into the cavities of the type as is desirable. As a rule a
fine quality of plaster of paris is to be recommended. What is sold as
dental plaster is the best, but common plaster can be used. It is mixed
with water or with a solution of gum arabic or dextrine in water. For
the latter enough gum should be added to make the mixing solution as
thick as thin syrup.

A piece of iron, perfectly flat and true, is now to be taken, large
enough to more than cover the inscription to be copied. Upon its
surface a putty made of the plaster and the liquid used in mixing is to
be spread. This should be rather stiff. The surface of the iron should
not be too smooth as it is desirable that the plaster should adhere
well on setting. The plaster should be smoothly spread to a depth of
three-sixteenths or a quarter of an inch. It is best applied with a
palette knife or trowel, although a table knife will answer perfectly.
If its surface does not become smooth it can be made so by applying a
little of the solution with the knife or trowel.

Before this has been done the model must be oiled. Olive oil or other
clear oil is applied to all parts of the type faces, and the excess
is then wiped off and cleared out of the interstices with a piece of
blotting paper.

Next the plate with the plaster is inverted and is pressed steadily
down upon the model until it strikes the distance pieces. It is left to
set. In about ten minutes it can be raised, when it will be found to
give a beautiful impression true to the smallest detail of each letter.

It has been said that water may be used as the mixing fluid. If this
is done it is well to strengthen the mould by saturating it with an
alcoholic solution of shellac, after it has dried thoroughly, best
for a few hours in an oven. This operates to strengthen the small
projections that are liable to crumble or to break off in use.

The dealers in rubber stamp supplies sell a lever press for conducting
the operation of producing the matrix. The type is locked in a special
chase, which is carried on a bed that travels under and out from under
the platen of the press upon rollers. From each corner of the chase in
which the type model is locked, a pin rises which is encircled by a
spiral spring. A square frame of flat iron with holes at the corners
for the pins to pass through, rests upon these springs well above the
type. The pins pass through holes in its corners. The matrix plate
with its coating of plaster is placed upon this frame, which supports
it above and not touching the type. The whole is now rolled under the
press and the lever pulled to produce the impression. As the pressure
is released the frame with the matrix is raised from the type by the
action of the springs. This can be done immediately, and before the
plaster has set. It is almost impossible to raise it by hand with the
requisite steadiness. The same chase with corner pins and springs can
be used in a screw press, the one press answering for making the matrix
and for moulding and curing the stamps. The plaster matrix can also
be made by casting from a thinner mixture of plaster and water. After
the type has been set up, or the model has been selected and placed
face up and horizontal, a little ridge or projection must be made all
around it. Paper can be pasted around it, and wound with thread for
this purpose. It is oiled and wiped off as before. The plaster is now
mixed with water to the consistency of cream, and is poured upon the
model until it lies even with the projecting ledges or paper border. In
an hour or less it can be removed. If water is used the mould should
before use be treated with shellac solution as already described. The
plaster may also be mixed with gum arabic solution, or with three
to ten per cent. of powdered marshmallow root. This increases its
toughness.

What is known as the oxychloride of zinc cement appears to the author
to be far preferable to common plaster of paris. It is a trifle more
expensive, but it costs so little that it is well worth trying. It
is made by mixing oxide of zinc with a solution of zinc chloride. No
particular strength of solution or proportions are prescribed; the zinc
chloride solution should be a strong one, and the mixture should be of
about the consistency of soft putty.

Zinc chloride may be bought as a solid substance or in strong solution.
The latter answers for the mixing directly. It may also be simply
made by dissolving metallic zinc in strong hydrochloric acid. The
manipulation is exactly the same as with plaster of paris.

The manufacture of papier maché and of other matrices is given in
a special chapter. For all ordinary purposes the plaster or cement
matrices are ample.

The stamp is made from the mixed uncured sheet rubber, whose
preparation in the factory, including the operation of calendering it
into sheets, has already been described. The best advice the reader can
be given is not to attempt to make it except as a matter of interest
and experiment. It can be purchased especially prepared for stamps from
the dealers in india rubber.

A piece is cut from the sheet large enough to cover the face of the
matrix. It should have a perfectly smooth surface, without cloth
wrapper marks sometimes found impressed on it. The sheet as received
from the maker is about one-eighth of an inch thick. It is thrown into
a box of powdered soapstone or talc to secure a coating of the same on
both sides. A little is dusted over the matrix and the excess is blown
off. The matrix is now placed upon the base of the press, and heat is
applied.

To carry out the process most simply the press if of metal may be
placed upon a support over a gas burner or kerosene lamp, or even on a
kitchen range or stove. It will in a few minutes become warm. The sheet
of india rubber is now dusted off and is placed in the press upon the
matrix. The platen of the press is screwed down upon it.

As the india rubber becomes hot it begins to soften and flow. By the
action of the screw of the press it must be forced down from time to
time as it softens. This drives the putty-like material into all the
interstices of the mould. The excess escapes from the sides of the
tympan in cases where the latter is of restricted area. The press
theoretically should be heated to the vulcanizing temperature, which
is 284° F. (140° C.). In practice the heat is not determined with a
thermometer. The operator learns by experience how much heat to apply.
The regulation type of gas heated press or stamp vulcanizer is shown in
the illustration on page 53.

As some of the india rubber is sure to protrude, the progress of the
work can be watched from its action. By pressing the point of a knife
against it the period of vulcanization can be told. Before the material
is heated it is elastic and resists the pressure of the knife; as heat
is applied it becomes soft like putty; as the heat increases it again
stiffens and becomes quite elastic. At this point the press can be
opened and the sheet and matrix can be taken out or the platen swung
aside. On pulling or stripping the sheet from the matrix it will be
found to reproduce the model in elastic india rubber to the minutest
detail.

[Illustration: OIL STOVE FOR HEATING VULCANIZERS.]

As regards the minor details there is something to be said. Distance
pieces to gauge the thickness have been recommended for the home-made
press, page 48. Care must be taken to have these low enough to provide
for enough excess of material to produce a good impression. For
ordinary stamp work they should allow about one-sixteenth of an inch
for the “squeeze.” It will be seen that by using the distance or gauge
pieces both for making the matrix and for moulding and curing the
stamp, absolute parallelism of surfaces will be secured.

The reader will have noticed in the description and will find at once
in practice that the press has to be screwed up as the rubber softens.
Where heavy iron presses are used the large mass of heated iron
comprised in the platen of the press instantly heats the upper surface
of the india rubber sheet and the heat immediately penetrates into it,
while the heated matrix heats it from below. Thus it softens at once,
and the press is directly turned down and the india rubber is driven
into the mould and curing at once begins. But where small presses are
used this manipulation is not so easy. For such the springs mentioned
on page 51, are highly to be recommended. The matrix and india rubber
can be put into the cold press, and the tympan with intervening springs
can be screwed down so as to compress them. Then on applying heat the
moulding takes place automatically.

With a hot press and good sheet a period of three to ten minutes is
ample for moulding and curing.

Instead of sprinkling with talc the matrix may be oiled and sprinkled
with plumbago and afterwards polished with a brush. This is not so
clean a material as talc and is not to be recommended for general use,
especially as oil is a bad substance to bring in contact with rubber.

The distance or gauge pieces whose use has been recommended are not
necessary where presses working truly parallel as regards their
opposing faces are used. But where home-made apparatus is used they
will be found a valuable addition.

In describing the simple press it was said that it could be made of
wood. It is evident that a wooden press could not be used for direct
heating. Such a press must be used in a hot chamber or vulcanizer,
properly so called. Originally rubber stamps were generally made in
chamber vulcanizers.

The next cut shows a combined matrix making, moulding and vulcanizing
apparatus of very convenient and compact form and adapted for rapid
work. As the press stands in the cut the matrix press is seen in front.
A box or chase is carried under its platen by two trunnions, so as to
be free to oscillate to a limited extent. The type model is secured in
this box. Above this box or chase is a cross-bar with screw and platen
attached, connected at will to two standards or pillars, so as to
constitute the matrix press.

A matrix plate swings on a hinge joint between the two presses. The
hinge-pin is removable. Its ends can be seen projecting to right and
left of the press columns. The hinge is at such a height that when the
matrix plate is swung forward over the type box it will rest upon it in
a nearly horizontal position. The pivoted box will adjust itself so as
to come into parallelism with the plate.

[Illustration: MATRIX MAKING, MOULDING AND VULCANIZING APPARATUS.]

When the matrix plate is swung back it falls upon the base plate of the
vulcanizing press seen in the rear.

In use the composition used for the matrix is spread upon the matrix
plate, which may for this purpose be removed from the apparatus. It
is replaced and the hinge-pin is pushed home. This is done with the
composition coated side facing the front of the apparatus as it stands
in the cut. The plate is then swung forwards, the platen of the matrix
press being turned forward out of the way, and is pressed down upon the
type or other model that rests in the type box. If desired the press is
used to force it home. The cross-bars of both the presses are arranged
to swing each one on one of the pillars, so that the platens are turned
to one side out of the way of the matrix plate as it is swung back and
forth.

The pressure is released and the platens are turned aside. The matrix
plate is swung over to the rear upon the bed-plate of the vulcanizing
press. Here it lies with the composition-matrix upwards.

A lighted lamp, either alcohol or gas, is placed beneath the bed-plate
of the vulcanizing press on which the matrix rests. This quickly dries
it and brings it to a good curing temperature. The cross-bar and platen
may be swung over it during the heating so as to be heated at the same
time. The matrix is talced when dry and hot; the mixed sheet itself
talced, is placed upon the matrix, the platen is screwed down upon it,
and in a minute or two the moulding and curing is completed.

[Illustration: RUBBER STAMP VULCANIZER.]

A vulcanizer, properly speaking, is a vessel arranged to heat to a
definite degree any desired articles which are to be cured. The
favorite type have been the steam vulcanizers. If steam is generated
from water at a constant pressure, other things being equal a constant
temperature will be produced. By raising or lowering the pressure
the temperature can be made to rise or fall. A steam vulcanizer is a
tightly sealed vessel which contains water and which is provided with a
thermometer or a pressure gauge as well as a safety-valve, safety disc
or safety plug. By keeping the gauge at constant pressure or by keeping
the thermometer constant the temperature can be limited and kept
steady. The following table gives some pressure in pounds per square
inch with temperatures corresponding to steam of such pressures:

  Lbs. per square inch.   Temp. Fahr.   Temp. Cent.

           45.512            275°          135°
           52.548            284°          140°
           60.442            293°          145°
           67.408            300.2°        149°

The illustration, p. 64, shows a vulcanizer of modern type made for
rubber stamp work. In some recent vulcanizers the water and steam are
excluded from the vulcanizing chamber, being contained within double
walls forming a steam jacket and maintaining a constant heat within the
chamber. These illustrate a point that has been much misapprehended,
namely that curing is independent of pressure or atmosphere. Because
vulcanizers have generally been filled with steam at high pressure
many have supposed that the steam or pressure had something to do with
their action. The fact is that it is only the heat due to the steam at
such pressure that is instrumental. Steam is a very powerful radiator
and absorber of so called radiant heat. For this reason an atmosphere
of steam maintains all parts of the vulcanizer at an even temperature
and is to that extent advantageous. Its presence and the pressure it
generates are not by any means required for vulcanizing. Its pressure
is entirely without effect.

[Illustration: STEAM JACKET VULCANIZER.]

To use a steam vulcanizer, water is introduced, the article in the
press or mould is placed in it, and the top is secured. Heat is then
applied, best if on the small scale, from a Bunsen gas burner gas, or
oil stove. Either the pressure gauge or thermometer may be watched, and
the flame turned up or down to keep it at the proper temperature.

Moulding cannot be executed in the ordinary closed chambers. The press
must first be heated to the temperature of boiling water or thereabouts
and the moulding is then effected by screwing down the mould screw,
upon the sheet and matrix. It is then placed in the vulcanizer and
cured.

The manufacturers supply gas regulators which automatically regulate
the gas supply. These are worked by the steam pressure. If any one
wishes to study the practical manipulation of small steam vulcanizers
he can see them in use at any dentist’s office.

There is no need of a steam vulcanizer for ordinary stamp work. The hot
press system already described answers every purpose and is in use by
the most advanced manufacturers for thin sheet work. But if a wooden
moulding press is used then it must be heated in a vulcanizer or some
kind of oven or hot chamber.

A very simple and reasonably satisfactory oven or air bath can be
made from a flower pot and a couple of tin plates. A plate larger
in diameter than the mouth of the flower pot forms the base of the
apparatus. This is supported on a stand over the gas lamp or other
source of heat. A smokeless flame or one depositing no lampblack should
be used. Alcohol or a kerosene oil stove illustrated on page 59 are
excellent. On this plate a smaller plate is inverted, which latter must
be so small as to be surrounded by the flower pot and to be included
within it when the pot is placed over it like an extinguisher.

[Illustration: FLOWER POT VULCANIZER ON STAND.]

A chemical or round stemmed thermometer is arranged to go through the
aperture in the upturned bottom of the pot. This may be hung from a
support or it may be secured by passing through a hole in a cork or
block of wood. Its bulb should be near the part of the chamber to be
occupied by the mould or press.

The press with the article to be cured is placed upon the inner plate.
The temperature is maintained at the proper point by regulating the
heat, and all the conditions for excellent work are supplied. The
disposition of the apparatus is shown in the cuts.

[Illustration: INTERIOR OF FLOWER POT VULCANIZER.]

Another arrangement equally simple is given in the next cut. An iron
kettle has a layer of type metal or lead poured an inch thick cast
within it upon its bottom. A thermometer passing through a hole in the
cover enters a cup of glycerine that stands upon the bottom. This gives
the temperature.

The object of having a thick or a double bottom is to prevent excessive
radiation of heat from any one part. The essential condition for good
operation is to maintain an even temperature throughout the chamber.

[Illustration: FISH KETTLE VULCANIZER.]

The thermometer is not an absolute necessity. By removing the press
from time to time and inspecting the overflow of india rubber the
progress of the operation can be watched. An extra piece of india
rubber may be placed on a piece of wood by the side of or upon the
wooden portion of the press, and its condition can be taken as the
criterion. Pressure with the point of a knife will tell the vulcanizing
point.

By the press system of curing, a heat far above the vulcanizing
temperature may be made to do good work by a very short application.
There is however danger of burning the work if left in too long. If
the air-bath with thermometer or the steam vulcanizer is used, and
the heat is kept down to the proper curing temperature, there is no
danger of burning the india rubber even if the curing is considerably
prolonged.

As the flower pot has often to be lifted off for introduction or
removal of the press, and as it gets quite hot, a holder of some kind
is requisite. A piece of heavy blotting paper is very convenient for
this purpose.

The flower pot system with thermometer can be further simplified by
being used on a stove or range. A china saucer inverted, or some
similar support, should be placed under the pot. A part of the stove at
very low heat will suffice. The kettle vulcanizer, can also be placed
on a stove so as to dispense with gas or oil.

Finally, as the last step in simplifying the work, a stamp can be made
without any special apparatus beyond a hot flat iron. The matrix may be
placed on a stove where the heat is rather low, the talc-coated mixed
rubber sheet placed upon it, and on this a hot flat iron. In a few
minutes if the heat is sufficient the stamp will be finished.

A few words may be said about the type. High spaces and quads between
the letters should be used, such as will come up to the shoulder of the
type, as has been said. But a very nice effect is produced by using
low quads between words. This leaves each word elevated by itself,
producing a good appearance.

Autograph stamps are made from a model cut in wood by a wood engraver.
The autograph is written in some form of copying ink upon a piece of
paper, and is transferred by moistening and pressure to a block of
wood. With an engraver’s tool the wood is cut away from the lines, as
the block is routed after the inscription has been “outlined.” The
woodcut is used as a model for making a matrix.

It is evident that an autograph of fair quality could be obtained from
a chalk plate. But in rubber stamp work to get good results certain
essential parts should be of the best. These parts include the mixed
rubber, model and matrix. A departure from excellence in any of these
tends to the production of an inferior stamp. What is known as a
“healthy cure” is above all essential to the appearance of the product.

The stamp thus made is attached to a wooden handle by common glue or by
one of the rubber cements given in chapter XVI.




CHAPTER VI.

INDIA RUBBER TYPE MAKING.


India rubber type are often used to set up different inscriptions in
wooden handles, or different date figures in rubber stamps. The latter
are in such cases made with slots or recesses to receive them. Rubber
type are much shorter than regular type, and as a rule are larger in
the body in proportion to the face of the letter. Where only a few are
required the following process is the simplest way of making them from
mixed rubber sheet.

The type which are to be copied are set up on a level base or imposing
stone, and quads or spaces are put between them. High quads and spaces
should be used; otherwise they should be pushed up until even with the
shoulders of the type. After oiling the faces a matrix is produced
exactly as described for stamps. Before it has set quite hard the
plaster or cement is cut off so that it will just fit within a little
“flask” or frame.

The latter may be made of tin or wood and may be rectangular or
circular, provided it is large enough to include within its area the
full working face of the matrix. It should be about half an inch or
five-eighths of an inch deep. Its object is to prevent the softened
india rubber from spreading, so as to secure the requisite height of
the type produced.

[Illustration: INDIA RUBBER TYPE MOULD.]

A piece of wood or metal is cut so as to fit closely within this frame
like a plunger. It is provided with shoulders or cross pieces, so as
to limit the depth to which it can be inserted. It will be seen that
when matrix, flask, and plunger are all put together a complete mould
for a block of type is produced, as shown in the illustration, the
matrix with its plate forming the bottom of the box. After the flask is
placed upon the matrix it is filled with the mixed uncured india rubber
sheet. As a matter of preference thick sheet is used, but scraps of all
shapes can be employed as it all fuses together. The mould and matrix
are of course first well dusted with talc powder. The plunger is put on
and the whole is pressed. Heat is next applied in a vulcanizer or hot
air chamber, such as the flower pot arrangement, or in boiling water.
As the sheet reaches the boiling point 212° F. (100° C.) the flask is
removed and the plunger examined. If it goes down to its seat without
expelling any india rubber more of the latter is required and is
accordingly inserted, the plunger being taken off for the purpose. The
softened gum should ooze out around the sides of the plunger. The whole
is again put under pressure, and the platen is screwed down, and if all
is right an excess of rubber showing itself, the whole is put in the
hot chamber, the heat is raised to 284° F. (140° C.), and is maintained
there for half an hour.

It is almost a necessity to secure the matrix plate to the bottom of
the flask. This for a single operation may be done by screws, or for
several operations by hooks or catches.

When the curing is complete the mould is removed from the vulcanizer,
is allowed to cool and is opened. The block of type will come out
with perfect reproduction of the letters upon one side. If all the
directions have been followed as regards distance pieces, level
imposing surface, etc., both faces will be exactly parallel, and any
number of other blocks can be reproduced of exactly the same height,
not necessarily from the same matrix, although one good matrix can be
used many times.

The type have now to be cut apart. This is done with a sharp knife
which is kept wet. It is worked with a sawing motion, and if sharp and
properly used will cut with regularity, and smoothly. Type with knife
marks on the sides are always unmechanical in appearance and seem to be
“home made.”

The object of using high quads and spaces or of pushing them up, will
now be evident. It secures the evenness of the general face of the
block of letters, which otherwise would have a deep depression between
each pair of letters. If the quads and leads are properly arranged, the
letters will project upwards from a smooth, plane surface.

The dealers in rubber stamp maker’s supplies sell special steel moulds
for the purpose of making them. This does away with all necessity for
making matrices, and making up a flask, etc. The general manipulation
is that given above. Where many are to be made the regular mould is by
all means to be recommended.

Sometimes type are made by cementing single letters made by the stamp
process upon wooden bodies.




CHAPTER VII.

THE MAKING OF STAMPS AND TYPE FROM VULCANIZED INDIA RUBBER.


Although all reference hitherto in the matters of stamps and type has
been to their manufacture from uncured india rubber, a good deal can
be done with vulcanized and cured gum. The stock that is known in the
trade as pure gum, such as is used for bicycle tyres, for steam packing
and the like, can be made to yield to moulding to a certain degree.
It will not flow and unite as will the uncured gum, but it is evident
that in certain cases its stiffness is even an advantage. Thus with it,
rubber type can be made without any flask or frame. The material has
stiffness enough to support itself.

The manipulation is of the simplest. A piece is cut out with a knife so
as to be of proper thickness and size. It should be a little thicker
than will ultimately be required. The two opposite surfaces should be
smooth and parallel. It is talced, and placed in the press with the
matrix beneath it, and subjected to pressure by the screws being turned
down. It is then placed in the vulcanizing chamber and heated to about
284° F. (140° C.). After it has become hot it softens a little. The
press is removed from the hot chamber and is again screwed down as hard
as the matrix can stand. This point is largely a matter of judgment.
The heat is largely indifferent as long as it is anywhere near the
above temperature.

By one or two repetitions of the pressing and heating the softened
india rubber can be made to take quite a deep impression from a
suitable matrix. It is allowed to cool under full pressure. When
removed from the press, it will retain the characters.

It is evident that impressions in as high relief or as deep and clear
as those yielded by uncured india rubber need not be expected. But
where the other cannot be had, or where some experimental or temporary
work only is on hand, this process will be very convenient.

The material may be half an inch thick. From such india rubber type can
be cut with advantage.

Old rubber can be thus used. The writer has obtained excellent results
from pieces of an old discarded bicycle tyre.

The great point is to apply a heavy pressure to the hot material. Many
other articles can be thus produced extemporaneously. At the same time
it must be considered only a makeshift. One who has used the soft,
easy flowing uncured gum would never be reconciled to the use of so
rigid and difficultly moulded a material, one too that can never be
trusted to reproduce intricate moulds of considerable depth. In the
slow yielding of the half melted uncured gum, so amenable to slight
pressure, a quality of availability is found that is missed in the
other. One is worked by main force where the other readily yields and
takes the most complicated shapes.

By the above process stamps of such thickness may be made that they can
be used without handles. It is also useful for impressing a designation
of any kind upon ready cured articles. It suggests a very useful
department of manipulation of india rubber.

The heating and moulding can be done also in a hot liquid bath such as
described in chapter XI.




CHAPTER VIII.

VARIOUS TYPE MATRICES FOR RUBBER STAMPS AND TYPES.


Matrices for stamp moulds can be made by several of the methods used by
stereotypers. Thus an electrotype could be taken directly from the face
of the type. There would be little or no utility in doing this where
the simpler processes are available.


PAPIER MACHÉ MATRICES.

The stereotyper for daily newspaper work uses very generally the
papier maché or “flong” process of reproducing the page. This is also
available for rubber stamp making.

The first requirement is paste. This is made by softening twelve parts
of whiting in forty parts of water, letting it soak for an hour or
more. Nine parts of wheat flour are added. This is best mixed with a
little water before adding to the main mixture. It is then brought to
the boil and seven parts of glue softened by soaking in twenty-one
parts of water, are added. For each gallon of such mixture, one ounce
of white crystallized carbolic acid is added if it is to be kept for a
long time.

The “flong” is made by pasting together, one on top of the other, a
sheet of fine hard tissue paper, three sheets of blotting paper (about
23 pounds to the ream), and a heavy sheet of manilla paper. The pasting
must be smooth and each layer must be pressed and rubbed down, but
not too hard. It is very important to secure perfect smoothness and
regularity, and entire absence of air bubbles.

Every printing office where the process is used has its own
traditions as to the preparation of flong. As a great deal depends on
manipulation, it would be well to endeavor to inspect its practical use
in a newspaper printing office before making it. Ready prepared flong
can also be procured.

The form of type must be very clean and there must be no paste on
the tissue paper face of the flong. The type are lightly oiled, some
powdered talc is dusted over the damp tissue paper face of the flong,
and the mass is laid face downward on the type. With a stiff haired
brush the paper is now beaten down against the type. Great care must be
taken to beat vertically; a slight side action will ruin the resulting
matrix. If the brown paper will not stand the beating, a cloth may be
spread over it.

The progress of the work can be watched by raising up a corner from
time to time. When sufficiently deep the last touch is given by the
printer’s planer. This is a block of hard wood. It is placed upon the
back of the flong and is hammered down. The operation is repeated until
the entire area has been treated. For much rubber stamp work the area
would be so restricted that shifting would be unnecessary.

The work is then put into a heated screw press, such as the vulcanizing
and matrix press, and is dried for a period varying from some minutes
up to half an hour. Some blotting paper is advantageously pressed
on top of the whole in the press while drying. The press is opened,
the flong removed, and dried in an oven. It is kept under a piece of
wire net while drying to keep it flat. The net may be of wire, .064
inch thick, with six meshes to the inch. This baking is not strictly
necessary for rubber stamp work.

This gives a matrix which may be used as rubber stamp moulds. In use it
is recommended to place a piece of smooth tin foil over it. This tends
to give a smoother surface to the rubber.


STRUCK UP MATRICES.

Didot’s polytype process may be advantageously used for producing type
metal matrices. The following is the method of applying it.

The type form is firmly locked and is backed up by and secured to a
solid block of wood. It is suspended in a sort of gallows frame with
the face of the type downward and exactly level a few inches above a
table. Underneath it a shallow tray is placed, into which some melted
type metal is poured. The melted metal is carefully watched. The block
and type are held by a catch so as to be released at will. Just as the
type metal is on the point of solidifying, the block is released and
drops upon the metal in the tray. The type should be slightly oiled.
The force of the blow produces a matrix in the metal, and the form can
at once be removed.

It is well to have accurately adjusted distance pieces for
corresponding striking pieces on the type block to impinge upon. The
process is highly spoken of, especially for small forms such as those
mostly required for rubber stamps.


CHALK PLATES.

The base for this form of matrix is a metal plate whose surface is
slightly roughened with sand-paper. It is next rubbed over with white
of egg, and flooded with the chalk wash made as follows: Flong paste
(described under Papier Maché Matrices, page 80), six ounces; whiting,
twenty-four ounces; water, three pints. The whiting is softened by
soaking for an hour or more. The whole must be intimately mixed. It
should cover the plate to the depth of one-thirtieth to one-twentieth
of an inch. The plate is dried in a perfectly horizontal position.

When dry the design or writing, etc., is made with a smooth steel
point, the lines being carried clear through the white layer to the
metal. The mould is now baked at a temperature well above boiling
water; as high as 392° F. (200° C.) may be reached without harm.

If the coating seems too thin, an extra coat can be given between the
lines especially over the larger areas. This must be done before the
baking. A pipette may be used for putting on this coat. This deepening
has the bad effect of increasing the chance of the coating stripping
from the metal.

The matrix thus prepared is used in the press just as is the ordinary
plaster matrix. It is suited for reproduction of autographs, scrip,
diagrams, etc.




CHAPTER IX.

THE MAKING OF VARIOUS SMALL ARTICLES OF INDIA RUBBER.


India rubber can be so readily shaped in moulds and the latter are so
readily made of plaster of paris that any one who is interested in such
things will find endless amusement in working out different designs.
Before suggesting any specific articles the following are the general
points to be kept in mind.

The material may be uncured mixed sheet of any thickness. As we have
seen this material when heated and pressed runs together. It can be
forced into any shape by comparatively slight pressure. So exactly does
it reproduce the smallest line or mark, that care must be taken to have
the moulds very smooth and free from defect. Powdered soapstone is used
to prevent adherence to the mould, but great care must be taken not to
mix it among the pieces of the india rubber, where several are used in
one article, as it will prevent their coalescing or running together.

Another point is to contrive to introduce the proper quantity of
rubber. The aim must be to have a slight excess, but to avoid
waste this should be as little as possible. Unless some rubber is
squeezed out there is no certainty that the mould has been filled.
Any projecting “fins” from the overflow are cut off with a knife or
scissors after the article is removed from the mould.

Plaster of paris or dental plaster mixed with dextrine or gum arabic
water or the zinc oxychloride cement, already described, is to be
recommended for the moulds. They should be made, if deep, in frames or
“flasks” of tin, as plaster if unsupported is liable to split open when
the rubber is forced home.

For many articles the hot press can be used. Such articles are mats
and other thin flat pieces. The rubber stamp sheet is a good material
for them. For thicker articles a thicker sheet can be used, and sheet
of any gauge can be procured from the maker. Much of what has been
said about india rubber type applies to the making of miscellaneous
shapes. It will also be understood where wooden moulds are spoken of
that plaster, or, still better, metal can be substituted, and is to be
recommended for nice work as the grain of the wood is very apt to show
where the india rubber comes in contact with it.

Suction discs and similar small articles into which an extra thickness
of india rubber enters are best cured in a vulcanizer. The flower pot
arrangement is excellent for such. The time for curing may be somewhat
extended on account of the greater thickness of material to be acted
on.

_Suction Discs._--For suction discs a mould is required which will
produce a shallow cup with the edge feathered or reduced to a very
slight thickness. Its outer surface should be raised in the centre
so as to give a projection for attachment of the hook. The discs are
generally made small, not over an inch in diameter, as they are not
reliable for any heavy service. Their principal use is to suspend
advertising cards and light articles to the glass of show windows. The
following is a method of making a simple mould.

A hole to give the outside contour should be bored in a small piece of
wood. A marble which will exactly fit the hole is next required. Some
plaster of paris is mixed with water and put into the bottom of the
hole, and the oiled marble is pressed down until the plaster rises and
fills the entire space under the marble. After it has set the marble is
removed. The proportions should be so arranged that the plaster will
have risen at the sides within an eighth of an inch of the surface of
the wood. This gives the exterior mould. For the cup or hollow a marble
a shade too large to enter the hole may be used.

One or if necessary two thicknesses of mixed sheet rubber cut into disc
shape so as to fit the hole are inserted in the block, and the larger
marble is placed on top and screwed down by the press. Heat is now
applied in the vulcanizer. When the thermometer indicates 212° F. (100°
C.), or better a little more, the mould is withdrawn and the screws
turned until the rubber is forced down and the excess begins to squeeze
out between the marble and the wood, which two should now nearly touch.
It is replaced and the heat is brought up to the curing temperature
284° F. (140° C.). It is possible that a second screwing up may be
needed. The spring press is in such cases particularly convenient as
it avoids the necessity for removing the press from the vulcanizing
chamber. After half an hour it will be thoroughly cured. A hole is made
through its centre from side to side thereof, but not penetrating the
disc, and through this hole a brass nail is thrust and bent into hook
form.

[Illustration: MOULD FOR SUCTION DISCS.]

In the cut the correct shape for the mould and consequently for a
suction disc is shown. This can be easily secured where a disc already
made is procurable by casting in plaster, or, with a little ingenuity
the template for the mould and the plunger to be used instead of the
marble can be whittled out of wood. The lower body of the mould in such
a case can be made of plaster of paris. To secure the alignment of the
two parts of the mould, dowel pins, indicated in dotted lines, should
be placed near the periphery. The gum should be introduced in a lump
near the centre, in order that it may sink well downwards to the bottom
of the mould before spreading laterally. Sometimes the tips have a
recessed end. This is secured by the use of a mandrel, shown in dotted
lines in the axis of the mould. Such discs are sometimes made to be
cemented to arrows to be discharged against smooth surfaced targets, to
which they adhere on impact by atmospheric pressure, giving rise to a
very interesting game.

Another use of suction discs is as photographic negative holders. They
can be fastened to a wooden handle and be attached by suction to the
back of a negative under treatment. For this purpose they should be at
least two inches in diameter.

_Pencil Tips._--These are generally little cylinders of india rubber,
which fit into a tube that slides over the end of the pencil. They can
be thus simply made. A hole is bored in a piece of wood the diameter of
and a little more than the depth of the pencil tip. A short cylinder
that exactly fits the hole is required for plunger. The gum is put into
the hole in little discs, or rolled up into a cylinder, the plunger is
placed on top, and the mould put in the press. It is shaped by pressure
and cured as described.

Sometimes the tips are cup shaped. For these the mould is made in two
sections fastened by catches or by pins set in the plaster as shown in
the cut. The hole is made larger at bottom than at top, and at the
top is a little smaller than the shaft of the pencil. A plunger that
nearly fits the small end is provided. The india rubber is placed in
the mould and heated. When soft, the plunger is forced down to the
proper distance in the press and the article is cured. Care must be
taken to give the plunger a good coating of talc, and it must be made
to sit vertically. The arrangement of a cylindrical hole shown in the
cut secures this result perfectly. As distance piece a pin is passed
through the plunger.

[Illustration: MOULD FOR PENCIL TIPS.]

_Cane and Chair Leg Tips, etc._--By carrying out the process just
described with larger moulds and of slightly different section very
convenient tips for chair legs and walking canes can be made. Such
tips can be modified in size and thickness to answer as covers for the
mouths of bottles, test-tubes, etc.

_Corks._--These may be made in moulds tapering from top to bottom.
The india rubber must be packed in with great care to secure as solid
filling as possible. A plunger is used that enters the larger end and
is a very little smaller in diameter, so as to descend a little way
into the mould. This distance determines the length of the cork. As the
perimeter of the plunger strikes the walls of the mould it cuts off
almost completely the excess of rubber that has squeezed up past it. An
excellent modification of the mould is shown in the cut. The upper part
with parallel sides serves as a guide for the plunger. It is a similar
extension as the one recommended to be used for the plunger in the
hollow pencil and chair leg tip moulds just spoken of.

[Illustration: MOULD FOR RUBBER CORKS.]

_Mats._--These may generally be made in the hot press. Designs for them
in great variety may be found in cut glass and pressed glass dishes.
Many of these have patterns on their bottoms that can be moulded in
plaster to serve as matrices.

_Cord, Thread and Seamless Tube._--By placing the mixed india rubber in
a cylindrical mould fitted with piston and with one or more round holes
in the bottom, the material may be softened by heat and forced out of
the holes by depressing the piston. This will form cylindrical thread
or cord. As it descends it may be received in a box of powdered talc
and be afterwards cured. By providing the hole with a mandrel seamless
tubing may be thus made. In making such the mandrel usually remains in
place during the curing. Plenty of powdered talc must be used.

_Skeletonized Leaves as Models._--These would form interesting models
from which matrices could be made in plaster. It would be possible to
produce some very pretty stamps or mats from these and similar models.

After some experience inspection of any article will show how it was
moulded. The fin will indicate the joint in the mould, and with this as
a clew the mould can be almost certainly constructed like the original.

_India Rubber Bulbs._--Bulbs and hollow articles generally, such as
dolls, toys and the like, cannot be made without special high pressure
hollow moulds. The general process consists in cutting out gores from
mixed sheet as for a balloon. The edges are coated with cement (thick
benzole or carbon disulphide india rubber solution) and while the
rubber is warm the seams are pressed and knitted together with the
fingers. A hole is left in one place through which some pure water
or water of ammonia is introduced. The bulb is now blown up with the
mouth or otherwise, and while inflated the hole is pressed shut. This
is often done with the teeth. Any projections around the seams are
cut off with curved scissors. The mould is of iron and in two halves.
Powdered talc is applied, and the bulb is placed in and shut up in the
mould which it should exactly fill. The mould is clamped together and
the whole is put into a vulcanizer, and the rubber is cured. The steam
and vapor formed by its liquid contents expand it and press it with
great force against the sides of the mould. After curing the mould and
bulb are removed from the vulcanizer, cooled by a shower bath of cold
water, the mould is opened and the bulb is removed. Often an iron pin
is left projecting through the side during the vulcanizing, which pin,
when withdrawn, leaves the necessary aperture, or it is perforated. The
bulbs are polished by tumbling in a revolving cylinder. Considerable
skill and practice are needed to succeed in making hollow bulbs. Great
accuracy is needed in cutting out the gores and in joining the seams.




CHAPTER X.

THE MANIPULATION OF MASTICATED SHEET RUBBER.


The manipulation of pure sheet rubber is simple, yet is liable to
lead to disappointment. When two pieces are laid face to face and cut
across with a sharp knife, or scissors, the edges will adhere with
considerable tenacity. This may be increased by applying some thick
solution of india rubber in a volatile solvent, and by manipulating the
sheets so as to bring the entire surfaces of the cuts together. Finally
the material may be charged with sulphur by absorption or by Parkes’
process, and cured in a glycerine or calcium chloride bath, all of
which are described in chapter XI. The same treatment will affect the
cement used in making the joint also, bringing about its vulcanization.

Such in a few words is the main process in the treatment of this class
of goods. Where it is desired to prevent adherence, soapy water or
powdered talc is used.

Adherence may be produced between the surfaces of the sheets if they
are clean, by pressure and a little warmth. The method of making toy
balloons will give an example of how the article is dealt with by the
manufacturer.

A pile of pieces of masticated sheet rubber is made. Every piece
has one side coated with powdered talc, and two talc-coated sides
are placed in contact in each pair. As they are piled up, the outer
surfaces of each pair are moistened with water. A steel punch or die,
pear shaped in outline, is used to cut down through the pile, cutting
all the pieces into that shape.

The pile is then taken apart in pairs. The separation takes place
between the wet surfaces, the edges of each pair adhering slightly
so as to enclose the talc-coated surfaces. The neck is opened if
necessary. A rather weak or thin solution of india rubber in benzole
is now brushed over the freshly cut edges. By pulling out the centre
of each piece the edges are brought into contact, and adherence is
produced.

If the Parkes process of vulcanizing, chapter XI., is employed they are
cured to the slight extent necessary upon a tray coated with talc. The
balloons are then ready for inflation.

They are rather delicate articles to make except for immediate use as
the thin material is liable to become over vulcanized.

In the chemical laboratory sheet rubber can be used for covering the
ends of glass stirring rods. These answer very nicely for cleaning out
from beakers the last particles of a precipitate. The sheet is cut of
proper size and is bent around the end of the rod and cut off close
with a pair of scissors. It adheres where cut. It is then pinched with
the fingers to bring the edges into better contact and the operation is
complete. A slight heat makes it adhere better.

To connect glass tubes in setting up laboratory apparatus the same
material was formerly used. It was wrapped around the joint, tied with
thread and slightly warmed. At present this form of connection is
wholly displaced by ready made rubber tubing.

It is interesting to observe in all articles made from this sheet the
marks of the original cutting knife. These may be observed in inflated
balloons, as parallel lines running all over the surface, and magnified
by the expansion due to the inflation.




CHAPTER XI.

VARIOUS VULCANIZING AND CURING METHODS.


The regular methods of vulcanizing and curing can be departed from and
good results obtained. A few excellent methods differing essentially
from the ordinary ones are described which will be of service to
workers on the small scale, as they enable one to dispense with
vulcanizer and air bath entirely.

One type of curing process does away with the air or steam vulcanizer,
and substitutes, as the curing agency, a hot bath of liquid. For
this purpose a fluid is required that will not act injuriously upon
the india rubber, and which will give a curing temperature without
boiling away. One favorite liquid is glycerine. This can be heated
to the necessary degree and is an excellent substitute for the
expensive apparatus often used. For experimental work it is exceedingly
convenient.

In use it is placed in a vessel of proper size and a thermometer is
suspended so that its bulb dips into the liquid near one side and
does not touch the bottom of the vessel. The heat is applied by a gas
burner, alcohol lamp or oil stove. Of course the vessel may be placed
on an ordinary cooking stove or range, and the heat may be graduated
and adjusted by moving it about until it reaches a part of the stove
where the proper heat will be maintained.

The mould with its contents is immersed in the glycerine, care being
taken to see that it so placed as to assume the mean temperature of
the liquid and not to be heated too hot. This might happen if it stood
on the bottom of the vessel, so it is well to have it supported or
suspended a little above it.

It is easy to see that the whole may be so arranged that the screw
handle or pressure nuts of the mould will rise above the liquid. In
this case the press can be screwed down while the article is heating.

Instead of glycerine a strong solution of some salt in water has been
recommended. A solution of calcium chloride, or some other salt can be
substituted. Either are very cheap and will be quite satisfactory.

Another treatment which applies also to the mixing operation is by the
sulphur bath. Sulphur is melted in an iron vessel and brought to a
temperature of 248° F. (120° C.). A piece of unmixed pure caoutchouc
immersed in this bath will gradually absorb sulphur. The case is almost
parallel with the absorption of water or benzole by the gum. The piece
swells and thickens as it is acted on and eventually will contain
enough sulphur for vulcanization. It may absorb as much as fifty per
cent. The point of proper absorption must be settled more or less
empirically or by successive trials.

After enough has been taken up the piece is removed and dipped into
cold water, which cracks the adherent sulphur so that it can be brushed
or rubbed off. This gives a piece of mixed rubber ready for moulding
and curing. It can be heated and moulded and may be cured as desired,
in a liquid bath, hot press or vulcanizer.

It will be observed that this provides for the admixture of sulphur
only; no talc or other solid can be thus introduced. The addition of
these solids tends to make the rubber of a more attractive color and
their use is not to be deprecated in all cases. Hence the sulphur bath
process is not to be considered a perfect one.

In the sulphur bath the mixing and curing processes can be combined.
If the liquid sulphur is heated to the vulcanizing temperature, 284°
F. (140° C.), a thin strip of gum immersed in it will be vulcanized
completely in a few minutes. A heating of several hours at the lower
temperature will effect the same result.

The sulphur bath processes must be regarded as unsatisfactory. It is
not easy to feel that any dependence can be placed upon them as regards
reliability or constancy of product. The sulphur also will mostly
effect the surface. Thin pieces may be satisfactorily treated, but the
same confidence cannot be felt as is experienced when specific amounts
of ingredients have been mixed in with pure caoutchouc in a regular
mixing machine.

The sulphur bath is of value to the experimenter, enabling him to do
his own mixing without expensive apparatus.

Bromine, iodine, chlorine and nitric acid are vulcanizers. A piece of
sheet rubber dipped into liquid bromine is instantly vulcanized. Iodine
and nitric acid have also been used in commercial work.

Alkaline or alkaline earth sulphides can be employed in solution under
pressure for vulcanizing. At a vulcanizing temperature their solutions
will answer for thin sheet very well. Polysulphides of calcium have
thus been employed.

By simply lying embedded in finely divided sulphur at a temperature of
233° F. (112° C.) as much as ten per cent. of sulphur may be absorbed
by thin sheet rubber. This is one of the processes peculiarly suited
for work on the small scale. It may be used instead of the Parkes
process next to be described.

Chloride of sulphur is an orange red mobile liquid of a peculiar and
disagreeable odor. It boils at 276° F. (136° C.). It dissolves both
sulphur and chlorine so that it is not easy to obtain it in a pure
state. If unmixed india rubber is exposed to its action it will quickly
become vulcanized. At ordinary temperatures the mixing action takes
place, though it is much accelerated by a slight application of heat.

It is quite possible that this action may be of use to the reader
in his manipulation of india rubber. Thin sheet may be vulcanized
by being immersed in a solution of this substance in bisulphide of
carbon followed by slight heating. The thin layer of caoutchouc left
by evaporation of the chloroform solution of india rubber may thus be
vulcanized so as to become comparatively strong and elastic. Where the
same solution has been used as a cement or for patching overshoes and
finishing the patch, a vulcanization can thus be given to it.

The process is known as Parkes’ cold curing process.

A solution of one part of chloride of sulphur in forty parts of
bisulphide of carbon is of good strength for rapid work. A thin article
needs but an instant of immersion. It then is placed in a box or tray
upon some talc powder and is heated to about 104° F., (40° C.). One
minute of curing will suffice. It is advisable to wash off the articles
afterwards in water or in weak lye to remove any traces of acid.

Petroleum naptha can be used as the solvent instead of bisulphide of
carbon. The latter substance has an exceedingly disagreeable odor, and
its vapors must be considered rather injurious especially to those who
are not accustomed to them.

When thick articles are to be cured by this process a much more
diluted solution is used. One per cent. or less of the chloride of
sulphur is the proportion used. The object of this is to enable a
longer immersion to be employed so that the interior will be affected
before the outer layers become too much charged with the vulcanizing
material.

In this short description of the Parkes curing process hints for a
useful method may be found. The process is beyond doubt by far the
simplest known for treatment of india rubber. Exactly what reaction
takes place is unknown. Whether the sulphur or the chlorine is the
acting vulcanizer has not as yet been determined.

Its defect is that it produces surface action, analogous to
casehardening. One method of avoiding this is to remove the articles
from the sulphur chloride bath and at once to immerse them in water.
This prevents the rapid volatilization of the solvent and an equalizing
of the absorption ensues.




CHAPTER XII.

THE SOLUTION OF INDIA RUBBER.


India rubber presents some difficulties in its solution. If a piece
of pure gum just as received by the factory is placed in hot water
it will swell and whiten after a while, but will not dissolve. If a
similar piece is placed in benzole a similar but greatly exaggerated
action takes place. The piece if left to soak for a day or more swells
enormously, but very little solution is effected.

The swollen india rubber can be removed from the benzole in a single
piece. It will display all the layers and marks of the original piece
which was perhaps of not one hundredth part of its volume. Some parts
will be a perfect transparent jelly.

It has been found that masticated india rubber dissolves with
comparatively little difficulty. If the experimenter will place in a
porcelain mortar, the jelly-like mass obtained as above detailed, and
will rub it up thoroughly, it will be effectually masticated. This
requires a little patience, as the slippery material seems to elude
the pestle. Yet eventually it will all be reduced to a perfectly
homogeneous mass. Its action while being rubbed up is very peculiar.
At first no progress seems to be made. After a little the lumps yield
to the friction. The rubber then begins to attach itself to the pestle
and mortar, and begins to be drawn out into ever changing webs and
threads. As the operation approaches completion the material makes a
snapping, crackling noise familiar to all rubber workers. When complete
there will be no lump left, and the whole will be a uniform pulp.

If benzole or a volatile solvent has been used, the rubber will
easily be removed from the mortar with a spatula or palette knife. If
turpentine was the solvent it will be impossible to remove the last
traces except after long standing or by solution.

If replaced in the original solvent it will now come into nearly or
quite perfect solution. This is the best way of masticating on the
small scale. It is almost impossible to masticate untreated gum in an
ordinary mortar.

The dealers sell a special india rubber for the manufacture of cement
and solutions. This is so treated by mastication that it dissolves with
great readiness. It is also said that heating under pressure is used to
dissolve it in some factories.

Many solvents have been used and none work without some difficulty.
Benzole, coal tar naptha, petroleum naptha, carbon disulphide, ether
and chloroform, oil of turpentine and caoutchoucin are the best known.
The naptha best suited for its solution is termed solvent naptha. It
has a specific gravity of .850 at 60° F. (15½° C.); it boils at from
240° F. (115½° C.) to 250° F. (121° C.) and on evaporation should leave
no more than ten per cent. of residue at 320° F. (160° C.)

Payen recommends a mixture of 95 parts bisulphide of carbon with 5
parts of absolute alcohol.

Commercial chloroform is apt to be too impure to act as a good solvent.
It is apt to contain alcohol mixed with it as a preservative, which
impairs its effectiveness.

Some of these solutions are better suited than others for the
deposition of thin layers by evaporation. Turpentine gives a very
sticky and unmanageable solution, which dries very slowly. Payen’s
solution and the chloroform and the benzole solutions may be cited as
especially adapted for this purpose. Careful vulcanization by the cold
curing method can be applied to articles made by such deposition from
evaporation.

In the case of all of them some form of mastication for the india
rubber is needed. The simple mortar grinding of the gum swelled by the
solvent is the only practical treatment without special apparatus.

When it is remembered that fixed oils are destroyers of vulcanized or
unvulcanized india rubber it will be obvious how important it is to use
pure solvents. Too great care cannot be taken to preserve the liquids
pure and free from such matter.

A solid hydrocarbon may be used. Thus paraffin wax, such as candles
are made of, when melted acts as a solvent. The resulting liquid
solidifies when it cools, retaining an almost greasy feel.

Boiling oil of turpentine is recommended by some for the solution of
vulcanized india rubber. Phenyle sulphide, it is stated, will soften it
so as to render it workable. The latter discovery is credited to Dr.
Stenhouse.

It is stated that a solution or pasty mixture of one part of caoutchouc
in eleven parts of turpentine with one half part of a hot concentrated
solution of sulphur (potassium sulphide) gives on evaporation a film
neither tacky nor soft, a species of vulcanization taking place.

It is of much interest to note that an aqueous solution of india rubber
has been proposed in which the vehicle is a solution of borax in water.
This is well known to be a solvent for shellac and other resins. It
has been recommended often as a vehicle for rubbing up india ink.
The ink made by mixing lampblack with the shellac solution is nearly
waterproof. A shellac varnish is given by the plain solution.

The experiments upon india rubber were published in a recent trade
paper. One method of making the solution is as follows.

A solution of borax two fifths saturated is made by adding to two
volumes of saturated solution three volumes of water. To this is added
a solution of india rubber in benzole or other hydrocarbon of such
strength and in such quantity as to contain from three and one-half
to four and one-half per cent. of india rubber referred to the borax
solution. It is now vigorously shaken and heated to 120°-140° F.
(49°-60° C.) and the agitation, not too violent, is continued until it
cools. Ceara or Madagascar rubber answers best; Para is not so good for
this formula. This may be termed the indirect or emulsion method.

For direct solution from two to three volumes of water may be added to
three volumes of saturated borax solution. The india rubber is added in
extremely thin shavings and the solution is heated. For weak solutions
the boiling point need not be reached. For strong solutions the heating
should be done under pressure so as to bring up the pressure to one to
three atmospheres.

Such solutions may contain as much as eight per cent. of the gum. The
mixture is liable to coagulate or gelatinize just at the wrong time,
but it may be of value as a vehicle or as a waterproofing agent. It
deserves further investigation, which it is to be hoped it will duly
receive.

Great care is necessary in working with naptha, benzole, carbon
disulphide and similar liquids. Their vapor is given off at ordinary
temperatures and may travel some distance to a lamp or fire and become
ignited and carry the flame back to the vessel. Their vapors are also
anæsthetic and should be avoided as regards inhalation.




CHAPTER XIII.

EBONITE, VULCANITE AND GUTTA-PERCHA.


_Ebonite and Vulcanite._--These two well known substances are india
rubber, in which the vulcanization process has been intensified. From
twenty-five to fifty per cent. of sulphur is added in the mixing, and
the curing is prolonged to several hours. A temperature of 275° F.
(135° C.) for six to ten hours is sometimes recommended, but generally
a shorter period at the regular temperature, 284° F. (140° C.), may be
employed.

The mixed sheet is made and sold extensively for dentists’ use. It
is soft and flexible and very easily moulded. It is treated like the
regular mixed sheet in every respect, except that plumbago brushed on
the slightly oiled surface of the mould is recommended instead of the
light colored talc, to prevent adherence. Wax where available is better
than oil.

Sometimes specimens are built up in sections. About an hour before full
vulcanization in the fourth stage, new material can be added and will
attach itself to the old. The stages of vulcanization are thus given by
Bolas.

“Several distinct stages or steps may be traced during the curing
of ebonite; and I wish to call your attention to some specimens
illustrating these various stages.

“Here, in the first place, is the plain mixture of sulphur and rubber,
this being nearly white, and capable of becoming quite plastic or soft
by the application of a gentle heat.

“The second specimen illustrates the action of a very moderate degree
of heat on the mixed material, this particular sample having been
heated to 128° Centigrade for twenty minutes. It is, as you see,
somewhat darkened, and has lost a little of its original softness;
while a degree of heat which would have rendered the original mixture
plastic, like putty, fails to make much impression upon it.

“The third specimen illustrates the effect of a more prolonged heating,
this sample having been heated for an hour to 135° Centigrade. It is
olive green in color, and has acquired a certain amount of elasticity,
resembling that of a rather inferior quality of vulcanized caoutchouc.

“The fourth stage of curing is illustrated by this specimen, which
you see is brown, and tolerably hard. Ebonite in this state refuses
altogether to become plastic by heat, and a temperature of 150°
maintained for half an hour or less would suffice to bring it to the
fifth stage, or that of finished ebonite.

“The fifth stage, or that of properly cured ebonite, is the goal
to be arrived at in manufacturing the material. There should be no
places where the curing is imperfect, a kind of defect which is likely
to happen when articles of unusual thickness are vulcanized, and no
portion of the ebonite should be spongy or honeycombed by air bubbles.

“The sixth, or spongy state, is generally the result of over-heating,
bubbles of gas forming in the material, and converting it into a kind
of porous, cinder-like mass.

“A specimen will now be handed round, which illustrates the third,
fourth, fifth and sixth stages, as already described. The specimen in
question was cured on a hot plate, this having probably been heated to
160° or 170° Centigrade; and you will be able to trace all gradations
in the curing operation, from the first setting of the plastic material
to the destruction of the ebonite by overheating.”

Cement for uniting pieces of the partially cured material may be made
by rubbing up some of the untreated scrap with benzole.

At the heat of boiling water, ebonite can be bent to a certain extent,
which bend it retains on cooling. When warm an impression of a coin or
relief die may be made on it by heavy pressure which it will retain. On
heating the image disappears. If before heating the surface is planed
off and the piece is heated the image formerly in intaglio will expand
into relief.

By the exact process of rubber stamp making excellent stereotype
plates may be made of ebonite.

It can be turned at high speed in a lathe and polished with fine 000
emery paper followed by a cloth bob with rotten stone, etc., and water
or oil. Blotting paper, charged with the above or with tripoli, is
excellent for polishing small surfaces by hand.

Ebonite is a good connecting material between softer rubber and iron,
the whole being vulcanized together; the iron should be well roughened
or cut into rasp-like or file-like projections.

Ebonite is properly the name for black hard rubber, and vulcanite for
the colored products such as used by dentists and others.


GUTTA-PERCHA.

Gutta-percha is prepared by coagulation from the juice or sap of
several trees, among others the _Isonandra gutta_, of Borneo and the
East Indian Archipelago. The product gutta-percha is identical in
composition with india rubber. It is hard at all ordinary temperatures.

Its manufacture includes purification and mastication. It is far more
amenable to treatment than is india rubber. Many materials are mixed
with it as adulterants or otherwise in the factories.

It is more useful in the form of sheets. These when heated to 122° F.
(50° C.) become pliable and can be moulded by pressure to any degree.
At the temperature of boiling water it becomes pasty and adhesive, and
at 266° F. (130° C.) it is so soft that it may be considered as melted.

It is an admirable moulding material. Stereotypes and other relief or
intaglio images can be made by pressing it while heated. These are
often absolutely perfect reproductions of the original.

Dishes for photographic purposes, etc., are easily made out of the
sheet. By gentle warming they become pliable, and a greater heat makes
surfaces capable of adhering by pressure.

Tubes can be made by the squirting process, as used for india rubber.
Wires are coated with it in a similar manner.

It has several defects. It is not durable if exposed to the air with
consequent changes of temperature. It is also too easily softened by
heat, as of course no hot liquid can be introduced into a gutta-percha
vessel. The Parkes cold curing process can be applied to it, which
makes it more indifferent to heat. This is applied by dipping an
instant and drying. After several repetitions the period of dipping
is prolonged and ultimately it is left immersed some time. If left
immersed at first it would dissolve.

It is soluble in most caoutchouc solvents, particularly in carbon
disulphide.




CHAPTER XIV.

GLUE OR COMPOSITION STAMPS.


Stamps made from a mixture of glue, glycerine, and molasses or from
similar mixtures are an excellent substitute for india rubber stamps.
Properly made they possess all the flexibility that characterizes the
rubber ones, while for fatty inks such as that used by printers and
lithographers, which inks tend to destroy rubber stamps, they are much
better. They are adopted by the United States government for making
dating stamps for use in the Post Office Department; by publishers
of directories for printing advertisements on the edges of their
publications, and in many other cases. Our description shall follow as
closely as possible the process and methods used in the United States
Post Office. They are there termed “composition blotters.”

The composition of which they are made is printer’s roller material.
Nine and one-half pounds of fine quality glue are soaked in just enough
soft water to cover it until it is thoroughly softened. It is then
melted. In the Government Department a steam kettle is provided for
the purpose. An ordinary glue pot will answer for smaller quantities.
When melted four and one-half pounds of best molasses and seven pounds
of glycerine are added, and the whole is thoroughly mixed. The formula
varies a little according to the prevailing temperature, less molasses
being added when the weather is warm, and _vice versa_. Experience is
here the best teacher. When well mixed it is poured out into tin pails
whose inner walls or sides and bottom have been rubbed over with oil.
It solidifies in cooling and becomes a clear brown jelly quite free
from any stickiness or superficial moistness.

[Illustration: MODEL FOR COMPOSITION STAMP MOULD.]

In use it is turned out of the pails to which, owing to the oiling, it
does not adhere. It is cut off as wanted, melted by heat and cast in
oiled moulds.

The latter are made of type metal to which one-third its weight of lead
has been added. As model for the mould or matrix a brass model of the
stamp is employed. This represents a sort of oval based cut-off or
truncated cone, about an inch high and a little over an inch long on
its base. A flange extends outward from its base and a tube is provided
to fit this flange. Its smaller end corresponds to the face of the
stamp, and on it are engraved in full relief any permanent characters,
circles or border lines, etc. Through its centre one or more apertures
are made. Into these, changeable steel, iron or brass type may be
introduced and set fast with plaster of paris.

[Illustration: COMPOSITION STAMP MOULD.]

To make the mould, the brass model with its movable type set as
required is placed upon a flat table or plate, face upward, and
surrounded by the tube, as shown in partial section in the cut, page
114. The tube is a strip of sheet iron, which is bent around the flange
and is secured in place by a wire twisted around it. The melted alloy
(type, metal and lead) is poured into the space thus formed until
it rises a quarter of an inch above the face of the model. In a few
minutes it sets and is removed and allowed to cool. This gives a cup
with the inscription and design depressed or in _intaglio_ upon its
inside base. This is shown in the cut, page 115, partly in section; it
will of course be understood that the mould forms a complete cup.

To make the stamp the interior surface of the mould is oiled with a
stiff brush. It is not material what oil is used. The composition
melted by heat is then poured into the cup, and is allowed to solidify.
Owing to the conical shape of the mould it is readily removed. The
mould must be hot but not too much so.

In the Post Office stamps the date requires to be changed frequently.
Some of the figures do duty for two or three days each month. Thus the
figure 8 is in the designation of three days, the eighth, eighteenth,
and twenty-eighth. There are three changes involved therefore in
connection with this day numeral. When a stamp mould or matrix is
cast the place of numerals that are to be changed is filled with a
blank space in the part where the type would otherwise come. A number
is stamped in this space when needed, by means of an ordinary steel
number-punch.

When the number is to be changed the old character is scraped or cut
out, leaving a small irregular hollow. A very small piece of soft
lead, about one-sixteenth of an inch on each side, is dropped into
the hollow. With a flat faced punch it is flattened out, and on it the
new number is impressed by a steel punch. This operation is repeated a
great many times before the matrix is worn out.

[Illustration:

  OPEN      SHUT

COMPOSITION STAMP HANDLE.]

In the cut, page 115, one number is shown as stamped into the soft
lead, and at the other end of the stamp is a blank space ready for a
number.

The casting of a stamp is so extremely simple that no attempt is made
to use movable type, as in permanent rubber dating stamps.

While it is obvious that these composition stamps could be attached
directly to wooden handles, a special style of handle, shown in the
cuts, is employed by the Post Office. A wooden handle carries at
its end a brass base, to which is pivotted a swinging piece that is
perforated by a conical oval aperture a little larger than the small
end of the stamp. The edges of this aperture are slightly rounded.

It is swung around as shown in the first figure, and the stamp,
previously moistened on its sides, is forced in. If the stamp is
properly made it is surprising how much force may be used to insert
it. If the edges of the brass swinging piece are not rounded there is
danger of the composition being cut. The stamp in its brass frame is
then swung back over the brass base, where it is secured by a catch.
The stamp is now ready for use, as shown in the second figure of the
cut.

It is imperative that no aqueous or glycerine ink be employed for
continuous work with such stamps. Common printers’ ink is perfectly
satisfactory, and the work may be nearly or quite as good as that
executed by an india rubber stamp.

The Post Office manufactures a pad for use with printers’ ink into
whose manufacture the same composition enters. The ink retainer is a
piece of fine felt, one-quarter to one-half an inch thick. This is
placed in the bottom of a shallow steel mould, where it enters for half
its depth into a recess that it accurately fits. The composition from
old stamps, melted up, is then poured upon and around it, the mould
being previously oiled. When it is full a piece of strong manilla
paper, of the area of the felt only, is placed upon the bottom of the
glue pad on its centre, which as it lies in the mould is its uppermost
part. The paper adheres strongly as the glue hardens. Eventually it
is turned out of the mould, and a pad, shown in the cut, is produced.
The dotted lines show the limits of the felt pad. The glue composition
underlies, surrounds and extends outwards from the felt portion. It
is found that the elasticity of the composition makes the pad much
pleasanter for rapid stamping.

[Illustration: COMPOSITION INK PAD.]

The above description gives the clew to making any stamp of this
description. The matrix may be of dental plaster, or of oxychloride of
zinc cement. The mould may be built up of type of any kind.

The composition is so cheap that the stamp can be made quite thick.
This gives it a high degree of elasticity and adaptability to uneven
surfaces. It may be mounted by adherence upon a flat board or block,
provided, if necessary, with handles. If the board or block is
placed upon the composition while it is still warm and liquid, as it
solidifies the board and composition will adhere with great tenacity.

All moulds or surfaces to which it is desired that the melted
composition shall not adhere must be oiled.

The moulds must not be cold or the composition will not enter the fine
divisions. If on the other hand they are too hot the mixture will
adhere. Experience will teach the right conditions for success.

Below are given other formulæ for roller composition. The formula
already given in this chapter is that used by the United States Post
Office Department.

I. “Old Home Receipt:” Glue 2 lbs., soaked over night, to New Orleans
molasses 1 gallon. Not durable, but excellent while it lasts.

II. Glue 10½ lbs., molasses 2½ gal., Venice turpentine 2 oz., glycerine
12 oz.; mix as directed above.




CHAPTER XV.

THE HEKTOGRAPH.


For obtaining multiple copies of writing, the apparatus called the
Hektograph or Papyrograph has been extensively adopted. In general
terms it consists of a tray filled with a jelly like composition. Any
imprint made upon the surface with aniline ink can be transferred to
paper by simple pressure. The tray filled with composition is called
the tablet. It is thus prepared.

The tray may be made of tin or even of pasteboard or paper, and should
be about one half an inch deep. It may be of any size, according to the
work it is to do. The composition is made from the best gelatine and
glycerine. One ounce by weight of gelatine is soaked over night in cold
water, and in the morning the water is poured off, leaving the swelled
gelatine. Six and one-half fluid ounces of glycerine are now heated
to about 200 F. (93 C.) on a water bath preferably, and the gelatine
is added thereto. The heating is continued for several hours. This
operates to expel the water and to give a clear glycerine solution of
gelatine.

The composition is then poured into the tray, which must be perfectly
level in order to obtain a surface nearly even with the edge. It is
then covered so as to keep off the dust. The cover of course must not
come in contact with the smooth surface. In six hours it will be ready
for use.

The original copy that is to be reproduced is made upon ordinary paper
in aniline ink. One formula for the ink reads as follows: Aniline
violet or blue (2 R B or 3 B) 1 oz., hot water 7 fluid oz.; dissolve.
After cooling add alcohol 1 fluid oz. and glycerine ¼ fluid oz., a few
drops of ether and a drop of carbolic acid. Keep in a corked bottle.
Other formulæ are given in chapter XVII.

The writing is executed with an ordinary steel pen. The lines should be
rather heavy so as to show a greenish color by reflected light.

The surface of the pad is slightly moistened with a wet sponge and
is allowed to become nearly dry. The paper is then laid upon it and
smoothed down. This is best done by placing a second sheet over it and
rubbing this with the hand. No air bubbles must remain between the copy
and the tablet, and the paper must not be shifted.

It is allowed to remain for a minute or less and is then raised by one
corner and stripped from the gelatine surface. It will have left the
reversed copy of its inscription perfectly reproduced upon the tablet.

At once a piece of ordinary writing paper of the desired size and
quality is laid upon the tablet, smoothed down, and stripped off,
when it will be found to have taken with it a complete copy of the
inscription or writing. This is repeated over and over again with
another sheet of paper, until the ink on the pad is exhausted. Fifty or
more good copies can be thus obtained.

[Illustration: THE HEKTOGRAPH.]

As soon as the work is completed the remains of the ink should be
washed off with a moist sponge and the tablet, after drying a little,
will be ready for a second operation.

Some practice is required to ascertain the proper strength of the
writing and degree of wetness of the surface. When the gelatine surface
becomes impaired it can be remelted in a water bath if it is not too
dark from absorption of ink.

_French Ministry of Public Work Formula._--Glue 100 parts, glycerine
500 parts, finally powdered kaolin or barium sulphate 25 parts, water
375 parts. Use a little hydrochloric acid in the water for washing off
the pad after use.

_Hektograph Sheets._--Four parts of glue are soaked in five parts of
water and three parts of ammonia until soft. It is then heated and
there is added to it three parts of sugar and eight parts of glycerine.
The mixture is applied to blotting paper. This is saturated with it,
and successive coats added until a smooth surface is produced on one
side. This is the side for reproduction. It is used like the regular
tablet except that it is claimed that sponging off the writing is not
necessary. Owing to the capillary action developed by the blotting
paper it is supposed to be self-cleaning by standing.




CHAPTER XVI.

CEMENTS.


Before cementing vulcanized rubber the surface should be roughened or
still better it may be seared with a red hot iron. For bicycle tyres
this is especially to be recommended.

_Cement for Cuts in Bicycle Tyres, Rubber Belts, etc._--Carbon
bisulphide, 5 ounces; gutta-percha, 5 ounces; caoutchouc, 10 ounces;
fish glue, 2½ ounces. After it is applied and has dried the excess can
be removed with a wet knife. Bad cuts should first be stitched up.

_Bicycle Tyre Cement to fasten Tyres to Rims._--Equal parts of pitch
and gutta-percha are melted together. Sometimes two parts of pitch are
prescribed. This cement has extended application.

_Cement for Paper Boats and for Mending Rubber Goods._--Fuse together
equal parts of pitch and gutta-percha, and to this add about 2 parts of
linseed oil containing 5 parts of litharge. Continue the heat until the
ingredients are uniformly commingled. Apply warm.

_Waterproof Cement._--Shellac, 4 oz; borax, 1 oz; boil in a little
water until dissolved, and concentrate by heat to a paste.

_Another._--10 parts of carbon disulphide and one part of oil of
turpentine are mixed, and as much gutta-percha is added as will readily
dissolve.

_Cement for Mending Hard Rubber._--Fuse together equal parts of
gutta-percha and genuine asphaltum; apply hot to the joint, closing the
latter immediately with pressure.

_Glue to Fasten Leather, etc., to Metals._--1 part crushed nut galls
digested 6 hours with 8 parts distilled water and strained. Glue is
macerated in its own weight of water for 24 hours, and then dissolved.
The warm infusion of nutgalls is spread on the leather; the glue
solution upon the roughened surface of the warm metal; the moist
leather is then pressed upon it and dried.

_Marine Glue, Various Formulæ._--I. Dissolve 1 part of india rubber
in 12 parts of benzole, and to the solution add 20 parts of powdered
shellac, heating the mixture cautiously over a fire. There is great
danger of conflagration. Apply with a brush.

II. Caoutchouc, 1 oz; genuine asphaltum, 2 oz; benzole or naptha, q. s.
The caoutchouc is first dissolved (as described in chapter XII.), and
the asphaltum is gradually added. The solution should have about the
consistency of molasses.

_Cement for Vulcanized India Rubber._--Stockholm pitch, 3 parts;
American resin, 3 parts; unmixed india rubber, 6 parts; oil of
turpentine, 12 parts. Heat and mix very thoroughly. More oil of
turpentine may be added as required.

_Gutta-Percha Cement for Leather._--Soak gutta-percha in boiling water.
Soften in benzole after cutting up for a day. Heat on a water bath
until the greater part of the benzole is expelled. When cool it will
solidify. Use by heating.

_Cement for Rubber Shoes._--

  (1) Chloroform                 280 parts.
      India rubber (masticated)   10   ”
  (2) India rubber                10   ”
      Resin                        4   ”
      Venice turpentine            2   ”
      Oil of turpentine           40   ”

For first solution dissolve by mastication. For second, melt the finely
divided gum with the resin, add the Venice turpentine and finally the
oil of turpentine. Use heat if necessary. Mix both solutions finally.
To apply, saturate a piece of linen with the cement and apply to the
spot previously coated with the cement. As it dries apply a little more
as required. A finishing varnish is given in the last chapter. Parkes’
cold curing process may be applied as described in chapter XI.

_Chatterton’s Compound_ for uniting sheets of gutta-percha in cable
cores and for general work with gutta-percha coated wires.--Stockholm
tar, 1 part; resin, 1 part; gutta-percha, 2 parts.

_Waterproofing for Wooden Battery Cells._--Resin, 4 parts;
gutta-percha, 1 part; boiled oil, a little.

_Another Formula._--Burgundy pitch, 150 parts; old gutta-percha in fine
shreds, 25 parts; ground pumice stone, 75 parts. Melt the gutta-percha
and mix with the pumice stone and then add the pitch, melting all
together. Apply melted and smooth off with a hot iron.

_Cement for Celluloid._--Shellac, 1 part is dissolved in spirits of
camphor 1 part, with 3 to 4 parts strong alcohol. It is applied warm
and the parts united must not be disturbed until the cement is hard.




CHAPTER XVII.

INKS.


RUBBER STAMP INK.

  Aniline blue soluble, 1 B     3 parts.
  Distilled water              10   ”
  Acetic acid                  10   ”
  Alcohol                      10   ”
  Glycerine                    70   ”

For other colors the following aniline colors may be substituted in
proportions given:

  Methyl violet, 3 B (violet)   3 parts.
  Diamond fuchsin I, (red)      2   ”
  Methyl green yellowish        4   ”
  Vesuvin, B (brown)            5   ”
  Nigrosin, W (blue black)      4   ”

For very bright red 3 parts of Eosin BBN. are used. In this case the
acetic acid must be omitted. In all cases the colors should first be
rubbed up with the water in a mortar, and the glycerine should be added
gradually. These inks will answer for the hektograph.

_Hektograph Ink._--Aniline color, 1 part; water, 7 parts; glycerine,
1 part. A little alcohol may be used with advantage to dissolve the
aniline color. It can be expelled by heating if it proves objectionable.

_Aniline Ink Vehicle._--Prof. E. B. Shuttleworth, of Toronto, Ont.,
suggests the use of castor oil in place of vaseline and other vehicles
for typewriter ink. The aniline colors may first be dissolved in
alcohol, and the solution may be added to the oil. They may also be
dissolved directly in the oil in which most of them are soluble.

_Indelible Stamping Inks._--I. Asphaltum, 1 part; oil of turpentine, 4
parts; dissolve and temper with printer’s ink. The ink may be omitted,
and solid dry color added.

II. Sodium carbonate, 22 parts; glycerine, 85 parts; dissolve and rub
up in a mortar with gum arabic, 20 parts. In a separate vessel dissolve
silver nitrate, 11 parts; in officinal aqua ammonia, 20 parts. Mix the
two solutions, and heat to the boiling point, 212° F. (100° C.). After
it darkens, add Venice turpentine, 10 parts. After applying to the
cloth, a hot iron should be applied, or it should be exposed to the sun.

III. Dr. W. Reissig’s formula:

  Boiled linseed oil varnish                    16 parts.
  Finest lamp black                              6   ”
  Ferric chloride (sesquichloride of iron)  2 to 5   ”

Dilute a little for use with varnish. After this ink has been removed,
no matter how completely it can be detected by dipping the paper into
a solution of ammonium sulphide.

IV.

  Aniline black in crystals    1 part.
  Alcohol                     30   ”
  Glycerine                   30   ”

Dissolve in the alcohol, and add the glycerine afterwards.

_Show Card Ink._--

  Pure asphaltum              16 parts.
  Venice turpentine           18   ”
  Lamp-black                   4   ”
  Oil of turpentine           64   ”

Dissolve the asphaltum in the turpentine, and thoroughly mix.

_Stencil Ink._--Shellac, 2 ounces; borax, 2 ounces; water, 25 ounces.
Dissolve by heat if necessary, first the borax alone, and then adding
the shellac. To the clear solution add gum arabic, 2 ounces. Color with
lamp-black, with Venetian red, or with ultramarine, to suit the taste.
Another formula gives shellac, 4 parts, borax, 1 part, and omits the
gum arabic.

_Copying Ink_ (for use without a press by simply pressing and rubbing
with the hand), by Prof. Attfield, F.R.S.--Use ink of any kind of extra
strength. This in many cases can be made by evaporating common ink
down to six tenths of its volume. Then mix with it two thirds of its
volume of glycerine, so as to restore the original volume.

_White Ink._--Barium sulphate, or “flake white” is mixed with gum
arabic water of sufficient thickness to keep it suspended, at least
while in use. Starch or magnesium carbonate or other white powder
may be used instead of the barium sulphate. The powder must be of
impalpable fineness.

_White Ink on Blue Paper._--A solution of oxalic acid in water is
used for this purpose. It may be applied with a rubber stamp or with
a common pen. A quill or gold pen is the best as a steel pen is soon
corroded. The ink bleaches the paper wherever it touches it, giving
white lines on a blue ground.

_Gold Ink._--Gold leaf with honey is ground up in a mortar, best an
agate mortar, or on a painters’ slab with a muller. It is added to
water, and thoroughly mixed and at once poured off from the first
sediments, filtered out, and washed. This is done to secure the
impalpably finely ground gold only. The resulting powder is mixed with
a suitable vehicle, such as white varnish or gum arabic water.

_Silver Ink._--As above, using silver leaf.

_Zinc Label Ink._--I. Verdigris, 1 part; ammonium chloride, 1 part;
lamp-black, ½ part; water, 10 parts.

II. Platinum bichloride, 1 part; gum arabic, 1 part; water, 10 parts.

_Diamond Ink for Etching Glass._--This consists essentially of
hydrofluoric acid mixed with barium sulphate to the consistency of
cream. The barium sulphate is quite inoperative except as giving a body
to prevent the ink from spreading. It is applied with a rubber stamp
or pen and allowed to remain for ten minutes or until dry. On removal
of the white powder, the design will be found etched on the glass. The
following is a formula for it.

Saturate hydrofluoric acid with ammonia, add an equal volume of
hydrofluoric acid and thicken with barium sulphate in fine powder.




CHAPTER XVIII.

MISCELLANEOUS.


_To Soften and Restore India Rubber Hose, etc._--I. Dip in petroleum
and hang up for a couple of days. Repeat process if necessary.

II. The above process is applicable to all articles, but is specified
for hose. It is stated that old rubber that has become hard may be
softened by exposure first to vapor of carbon disulphide, followed by
exposure to the vapor of kerosene. The latter vapor is found to be a
general preservative for india rubber.

III. Dr. Pol recommends immersion in a solution of water of ammonia, 1
part, and water 2 parts, from a few minutes to an hour.

_To Prevent Decay of Rubber Tubing._--The decay of rubber tubing has
been attributed to the formation of sulphuric acid from the sulphur
mixed with it. M. Ballard has suggested washing with water or weak
alkaline solution five or six times in a year.

_Joints between India Rubber Tubing and Metal._--Where tubing is
temporarily slipped over metal gas pipes and similar connections, as in
the chemical laboratory, it is well to apply glycerine to the metal.
It acts as a lubricant in slipping the tubing on, and assists in its
withdrawal.

_Preserving Vulcanite._--Wash occasionally with a solution of ammonia
and rub with a rag slightly moistened with kerosene oil.

_Effect of Copper upon Rubber._--In a paper read before the recent
meeting of the British Association, Sir William Thomson stated that
metallic copper, when heated to the temperature of boiling water, in
contact with the rubber, exerted a destructive effect upon it. With a
view to finding whether this was due to the copper _per se_, or to its
power of conducting heat more rapidly to the rubber, he laid a sheet
of rubber on a plate of glass, and on it placed four clean disks, one
of copper, one of platinum, one of zinc and one of silver. After a
few days in an incubator at 150° F., the rubber under the copper had
become quite hard, that under the platinum had become slightly affected
and hardened at different parts, while the rubber under the silver
and under the zinc was quite hard and elastic. This would warrant
the inference that the metallic copper had exerted a great oxidizing
effect on the rubber, the platinum had exerted a slight effect, while
the zinc and silver respectively had no injurious influence on it.
The rubber thus hardened by the copper contained, strange enough, no
appreciable trace of copper; the copper, therefore, presumably sets up
the oxidizing action in the rubber without itself permeating it.

_Gas Tight Tubings._--Fletcher has invented a gas tight rubber tubing
in which a layer of tinfoil is interposed between two concentric rubber
tubes, all vulcanized together.

_Printing Colors upon India Rubber._--It may sometimes be desirable
to have a surface of vulcanized india rubber so prepared that it will
take colors such as are used for calico printing. This end is simply
attained by sprinkling the article with farina before vulcanizing. A
small quantity attaches itself and forms an excellent base for color
printing.

_Gutta-Percha for Coating Glass._--For focusing glass in photography
and for similar purposes where ground glass or a translucent material
is required, a solution of gutta-percha in chloroform is highly
recommended. This is flowed over or painted on the glass and is allowed
to evaporate afterwards.

_Burned Rubber._--A very soft pure gum sold for artists’ use is
improperly termed burned rubber. It is used in crayon work for removing
and lightening marks by dabbing it against the paper, cleaning the
rubber from time to time. It is so soft that it picks up and removes
crayon marks without the necessity of friction. Thus the rubbing out
or more properly erasing operation can be localized and crayon tints
can be lightened in tone without impairment or “smutting.” It is a
very elegant accessory to the artists’ paraphernalia. To make it, pure
virgin gum, preferably the best Para, is cut into pieces and soaked
for some hours in benzole. A long soaking is advisable. The pieces
are then removed from the benzole and are ground in a mortar until
perfectly homogeneous. The mass is gathered up with a spatula and
is pressed into little tin boxes. If desired it may be dried upon a
water bath. This is not necessary as, if the box is left open, it will
rapidly season itself. It should be very soft, should tend to adhere
to the fingers, yet should leave them easily, and should strip cleanly
from the box. A very little turpentine makes it more adhesive. It may
even be softened in turpentine alone. This gives a gum that seasons
more slowly and is in some respects preferable to the benzole made
preparation. It is sold at a high price by the dealers, as the demand
for it is limited.

_Rubber Sponge._--This is also an artist’s rubber. It is also used for
cleaning kid gloves. It is made by incorporating with the masticated
or washed and sheeted gum any material or materials that will give off
vapor in the curing process. Damp sawdust and crystallized alum are
used as giving off vapor of water or steam, or ammonium carbonate as
giving off vapors of ammonia carbonic acid gas and steam. The mixed gum
may be cured in moulds, which it will fill by its expansion.

_Shellac Varnish for India Rubber._--This is made by soaking powdered
shellac in ten times its weight of strong aqua ammonia (26° B.). At
first no change beyond a coloring of the solution is perceptible. After
many days standing the bottle, which should have a glass stopper,
being tightly closed, the shellac disappears, having entered into
solution. It may be a month before complete solution. This forms an
excellent varnish for india rubber shoes and similar articles. It may
be applied with a rag. It is also a good application for leather in
some cases and doubtless many other uses could be made of it. It would
act well as a vehicle for a dark pigment such as lamp-black. It will
rejuvenate a pair of india rubbers very nicely. The ammonia exercises
also a good influence on the rubber. It has been recommended as a
cement for attaching rubber to metal, but its adhesive powers are not
always satisfactory.

_Simple Substitute for Stamps._--A very simple though rough and
imperfect substitute may be made by gluing with common carpenter’s glue
pieces of thick string upon a piece of wood, the string being given the
form of the desired letters. Care must be taken to avoid saturating and
stiffening the string with the glue.

_India Rubber Substitutes._--One of these under the name of vulcanized
oil is thus described by Bolas:

“Vulcanized oil is, perhaps, of more interest, and many oils, such as
linseed and others resembling it, may be vulcanized by being heated
for some time to 150° Centigrade with twelve to twenty per cent. of
sulphur. The product obtained is soft, and somewhat resembles very
bad india rubber. By increasing the proportion of sulphur very much
indeed, say to four times the weight of the oil, and vulcanizing at a
higher temperature, a hard substance, resembling inferior vulcanite, is
obtained.

“Soft and hard vulcanized oil have been introduced into commerce at
various times and under many names; but these materials never seem to
have made very much headway.”

Another method of treating the oil consists in mixing it with a
solution of chloride of sulphur in carbon disulphide or in naptha. On
standing, the volatile solvents escape, leaving a thick mass, which is
the substitute.

In combinations of aluminum with the fatty acids, forming aluminum
soaps, and of these, aluminum palmitate especially, a substitute for
india rubber has been sought but without success.

_Metallized Caoutchouc._--Unvulcanized gum is mixed with powdered lead,
zinc, or antimony. The mixed india rubber is then cured as in the
regular process.


EMERY WHEELS AND WHETSTONES.

Bolas thus describes their manufacture:

“When ordinary vulcanized rubber is heated to 230° Centigrade, (446°
F.) or until it melts, a permanently viscous product is obtained, and
this substance, if mixed with emery and sulphur to a kind of paste,
forms a material out of which the so-called agglomerated emery wheels
or grinders may be formed, the mixed materials being next hardened or
cured by the application of a steam heat. Emery wheels and hones made
on this principle were introduced by Deplanque about twenty-three years
ago.

“Thirty-five parts of old vulcanized caoutchouc having been placed in a
kind of still, heat is applied to melt it, the operation being assisted
by the gradual addition of about ten parts of heavy coal oil; but this
latter is afterward distilled off. The softened caoutchouc is then
incorporated with 500 parts of emery of the required degree of fineness
and nine parts of sulphur. These materials having been thoroughly
mixed, the hones or wheels are manufactured, and afterward cured or
baked at a heat of 140° Centigrade, (284° F.) during a period of about
eight hours. Grinding wheels, made in the above manner, can be worked
at a speed of 2,000 revolutions per minute, and are extremely useful
for the working of hardened steel or other obdurate materials.”

_Etching on Metals and Glass._--India rubber stamps can be used for
placing the ground upon knife blades and similar articles which are
to be etched. The parts untouched by the stamp are attacked by the
acid. In the case of glass, diamond ink (page 133) can be put on
with a stamp. The acids for metal etching might be thickened with
barium sulphate also and applied in the same way. In these cases the
inscription of the stamp would be etched. Where ground is put on,
whether on glass or metal, the design for the stamp will be protected.

_Etching Ground for Metals._--Equal parts of asphalt, Burgundy pitch
and beeswax melted together and mixed thoroughly. It may be softened
with mutton suet. Beeswax may be used, dissolved in ether or simply
melted. Yellow soap is sufficient for ordinary work.

_Etching Solutions for Biting in._--For steel and iron, _a._ sulphate
of copper and common salt in solution. _b._ sulphate of copper,
sulphate of alumina, and common salt, of each two drachms; acetic acid,
1½ oz. _c._ sulphuric acid, diluted with five volumes of water with a
little sulphate of copper. For other metals, except gold and platinum,
nitric acid diluted with five volumes of water.

_Etching Ground for Glass._--Melted beeswax is generally recommended.
It can be removed with spirits of turpentine after as much as possible
has been scraped off.

_Etching Glass._--Glass may be conveniently etched by exposing it to
the vapor of hydrofluoric acid. A shallow leaden tray, as large as the
glass, is required. A quantity of fluorspar is placed in it and is
moistened with concentrated sulphuric acid. The glass is placed face
downward over the tray. It is supported over the mixture by resting on
the edges of the tray or by any simple method, and the whole is covered
with a towel. In half an hour or more the etching will be completed.
The vapors must not be allowed to escape into any room containing
glass or metal articles as they corrode everything. Great care should
be taken also not to let the mixture touch the hand, as painful ulcers
are the result.

_India Rubber Shoe Blacking._--Raw india rubber is given as a
constituent of several shoe blackings. Formulæ are given as below for
paste and liquid blackings.

I. Paste blacking: bone-black, 20 parts; molasses, 15 parts; vinegar,
4 parts; sulphuric acid, 4 parts; caoutchouc oil (as given below), 3
parts.

II. Liquid blacking: bone-black, 60 parts; molasses, 45 parts; gum
arabic dissolved in water, 1 part; vinegar, 50 parts; sulphuric acid,
24 parts; caoutchouc oil, 9 parts.

Caoutchouc oil is made by dissolving or digesting virgin rubber 55
parts in linseed oil 450 parts.

_Waterproof Composition for Boots._--One ounce of virgin rubber cut
into pieces is digested in enough oil of turpentine to form a stiff
paste. In applying heat take great care lest the contents of the vessel
become ignited. When homogeneous, which condition may be brought about
by rubbing in a porcelain mortar, as described in chapter XII., it is
mixed with 5–6 ounces of boiled linseed oil. This gives an ointment
almost of the consistency of butter.




INDEX.


                                                                  PAGE
  Absorption of sulphur process                                    100

  Absorption of water by india rubber                               31

  Africa, ways of collecting rubber sap                          15–17

  Analysis of sap of india rubber tree                              27

  Apparatus for stamp making                                     61–63

  Artists’ burned rubber                                       136–137


  Balloons                                                          95

  Bands, india rubber                                               41

  Bicycle tyre cement                                              125

  Blacking, india rubber                                           142

  Borax and water solution of rubber                           106–107

  Brazil, ways of collecting sap                                 20–21

  Bromine as vulcanizer                                            100

  Bulbs, how made                                                92–93

  Burned rubber, artists’                                      136–137


  Calendering                                                       43

  Cane tips                                                         90

  Caoutchin                                                         30

  Caoutchoucin                                                      30

  Caoutchouc, (see India Rubber.)

  Cements                                                      125–128

  Clamp for vulcanizing press                                       52

  Cohesion of rubber, its importance to the manufacturer         26–27

  Cold curing                                                  100–102

  Composition for stamps and its moulding                      113–120

  Composition inking pad                                       118–119

  Composition stamp handle                                     117–118

  Cord, rubber                                                      92

  Corks                                                          90–91

  Curing                                                            44

  Curing, how to judge of completion of                             70

  Curing in liquid bath                                             97

  Curing in sulphur bath                                            99

  Curing, temperature of                                            58

  Central America, ways of collecting rubber                     18–19

  Chair leg tips                                                    90

  Chalk plates                                                   83–84

  Chlorine as vulcanizer                                           100

  Chloroform as a solvent                                          105

  Coagulation of sap by a plant                                     19

  Coagulation of sap by alum                                     22–23

  Coagulation of sap by fire                                     21–22

  Coagulation of sap by salt                                        18

  Cohesion of pure rubber                                           25


  Dating stamps, composition                                   116–117

  Didot’s polytype for matrices                                  82–83

  Distillation products of india rubber                          29–30

  Dolls, how made                                                92–93


  Ebonite                                                      108–111

  Ebonite, polishing                                           110–111

  Emery wheels and whetstones                                  139–140

  Emulsion of caoutchouc                                            10

  Etching                                                      140–142


  Fins, removal of                                                  86

  Flask for type moulding                                           74

  Flong matrices                                                 80–82

  Flong paste                                                       80

  Fluid for mixing with plaster for matrices                        55


  Gas heated steam vulcanizer                                       53

  Glue, marine                                                     126

  Glue stamps                                                  113–120

  Glycerine bath for curing                                         97

  Goodyear, Charles                                              13–14

  Gutta-percha                                                 111–112

  Gutta-percha, moulding                                       111–112

  Gutta-percha, vulcanizing                                        111


  Hektograph, composition                                 121–122, 124

  Hektograph, how made and used                                121–124

  Hektograph ink (also see inks)                                   121

  Hektograph sheets                                                124


  India Rubber, absorption of water by                              31

  India rubber, African                                          15–17

  India rubber, artists’ burned                                136–137

  India rubber, availability for small articles                     85

  India rubber, cohesion of unvulcanized                            25

  India rubber, composition of                                      27

  India rubber, discovery of, etc.                               11–13

  India rubber, effects of temperature on                        28–29

  India rubber, elasticity of                                   29, 33

  India rubber sap, its coagulation                                 11

  India rubber sheet, how made                                      40

  India rubbers, original way of making                             10

  India rubber stamp making without apparatus                       71

  India rubber stamps, home-made mould                           48–50

  India rubber stamps, starting point                               47

  India rubber, trees producing                                      9

  India rubber tree sap, analysis of                                27

  India rubber type                                                 73

  India rubber, vulcanized, general properties of                32–33

  India rubber, where collected                                     11

  India rubber, inelastic, how made                                 31

  India rubber, its mastication                                  38–40

  India rubber, manufacture of                                   35–46

  India rubber, necessity of drying                                 38

  India rubber, points to be followed in moulding small articles    85

  India rubber, preliminary operations in manufacturing          35–36

  India rubber, preserving, etc.                               134–135

  India rubber, properties of                                       28

  India rubber sap                                                9–11

  India rubber stamp vulcanizing                                 58–60

  Inelastic state of india rubber                                   31

  Inks, special for stamping, etc.                             129–133

  Iodine and haloid vulcanizers                                    100

  Isoprene                                                          30


  Leaves, skeletonized as models                                    92

  Liquid bath curing                                                97


  Machine for cutting sheet and threads                             40

  Machine for making mixed sheet                                 42–43

  Machine for masticating                                        38–40

  Machine for washing and sheeting                                  37

  Mackintosh                                                        13

  Mackintoshes, how made                                         45–46

  Marshmallow root for mixture with plaster                         57

  Masticated rubber, its easy solution                         103–104

  Masticating in mortar with benzole                           103–104

  Mastication of rubber                                          38–40

  Materials mixed with india rubber                                 43

  Matrices, various kinds of, for stamps                         80–84

  Matrix for stamp-making                                        54–55

  Matrix making by casting                                       56–57

  Matrix press                                                      56

  Matrix, process of making, for stamps                          54–55

  Mats                                                           91–92

  Metals, welding and cohesion of                                25–26

  Miscellaneous                                                134–142

  Mixed sheet                                                    42–44

  Mixed sheet for stamps                                         47–48

  Mould, home-made for stamps                                    48–50

  Moulding and curing stamps                                     58–60

  Moulds for composition stamps, temperature of                    120

  Moulds, material for                                              86


  Naptha and volatile solvents, danger of                          107

  Naptha, solvent                                              104–105

  Nicaragua, ways of collecting sap                              19–20

  Nitric acid as vulcanizer                                        100


  Oil for composition stamp moulds                             119–120

  Oil for mould face                                                55

  Oils fixed bad effect on solutions                               105

  Oxychloride of zinc cement for matrices                           57


  Papier maché matrices                                          80–82

  Paraffin and rubber                                          105–106

  Parkes’ process                                              100–102

  Payen’s solvent                                                  105

  Pencil tips, moulds for                                        89–90

  Phenyle sulphide as softener of vulcanized rubber                106

  Plaster, dental for matrices                                      54

  Press for moulding stamps, etc.                                51–52

  Press, gas-heated                                              52–53

  Press, home-made                                                  49

  Press, matrix making                                           55–56

  Products, general division of                                  35–36


  Rods, stirring for laboratory                                     95

  Rubber, origin of name                                            12

  Rubber, see India Rubber


  Salt bath for curing                                              98

  Sap of india rubber tree, analysis of                             27

  Sheeting and washing                                           37–38

  Sheet rubber, how made                                            40

  Sheet rubber, its joining                                         94

  Shellac for strengthening matrix                                  55

  Shoes, blacking for                                              142

  Shoes, india rubber, cement for                                  127

  Siphonia, origin of name                                          11

  Solution, different views of                                   31–32

  Solution, difficulties of                                        103

  Solvents for rubber                                          104–105

  Spring chase for matrices                                         56

  Springs for stamp moulds                                          51

  Springs on moulding press                                         51

  Sponge india rubber                                              137

  Stamp making                                                      47

  Stamps, rubber, substitute for                                   138

  Stamps, see India Rubber, Composition and general titles.

  Strauss’ method of coagulating sap                             22–23

  Suction discs, regular mould for                               88–89

  Suction discs, simple mould for                                87–88

  Sulphides, alkaline as vulcanizers                               100

  Sulphur, absorption process                                      100

  Sulphur bath for mixing and curing                            98–100

  Sulphur chloride process                                     100–102

  Sulphur, how mixed with gum                                       43

  Sulphur, its escape from vulcanized rubber                     33–34

  Sunlight excluded from washed sheet rubber                        38

  Syringes made by Indians                                          11


  Test for curing with knife                                        48

  Thread, rubber, cut                                               41

  Thread, rubber, moulded                                           92

  Tissues, coated, how made                                      45–46

  Tubes, connecting glass                                           96

  Tube, seamless                                                    92

  Turpentine, a solvent for vulcanized rubber                      106

  Turpentine compared with caoutchoucin                             30

  Turpentine, viscid nature of solution                        104–105

  Type, india rubber                                                73

  Type moulding flask                                               74

  Type and stamps from vulcanized rubber                            77

  Type, cutting apart                                               75

  Type, points in moulding                                          75

  Type, quads, and spaces for stamp models                       71–72

  Type, steel moulds for                                            76


  United States composition stamps                             113–120


  Varnish shellac for india rubber                             137–138

  Vulcanite                                                    108–111

  Vulcanization, its two steps                                      42

  Vulcanization, steps in process                                47–48

  Vulcanized rubber stamps and type                                 77

  Vulcanizer                                                     52–53

  Vulcanizer, fish kettle as a                                   69–70

  Vulcanizer, flower pot                                         68–70

  Vulcanizer, chamber                                               63

  Vulcanizing and moulding stamps                                58–60


  Washing and sheeting                                           37–38

  Water absorbed by india rubber                                    31

  Waterproof composition for shoes                                 142

  Waterproofing for battery cells                              127–128


  Zinc, chloride                                                    57






Transcriber’s Notes


Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.

Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.

Illustrations in this eBook have been positioned between paragraphs
and outside quotations. In versions of this eBook that support
hyperlinks, the page references in the List of Illustrations lead to
the corresponding illustrations.

The index was not checked for proper alphabetization or correct page
references. Three missing page references were added by the Transcriber.

Page 26: “The relegation of ice” was printed that way.

Page 40: “alkanine” may be a misprint for alkaline.