gently for 2 hours, in an evaporating dish, a mixture of 1,800 grains
rosin and 300 caustic soda with 20 fluidounces water. Upon cooling,
the soap separates as a yellow mass, which is drained from the liquid,
squeezed, then heated on a water bath until it is dry and friable.
Fixed oils may be emulsified by adding 1 ounce {290} to a solution
of 10 grains soap in 1 ounce water. Volatile oils require 10 grains
rosin soap, 2 3/4 ounces water, and 2 drachms oil. Creosote requires
double this amount of soap. Thymol may be rendered miscible with water
by dissolving 18 grains together with 20 grains soap in 3 fluidounces
alcohol, then adding enough water to make 6 fluidounces. Of course many
other substances may be emulsified with the same emulsifier.
«Yolk of Egg as an Emulsifier.»—The domestic ointment of Unona,
consisting of a mixture of oil and yolk of egg, is miscible in all
proportions with water. It is proposed to utilize this fact by
substituting a diluted ointment for the gum emulsions in general use,
the following being given as a general formula:
Yolk of egg 10 parts
Balsam Peru 1 to 2 parts
Zinc oxide 5 to 10 parts
Distilled water 100 parts
If desired, 33 parts of vinegar may be substituted for the same
amount of water, while oil of cade, oil of birch, lianthral or storax
may be substituted for the balsam Peru, and an equal quantity of
talc, magnesium carbonate, sulphur of bismuth subcarbonate, may be
introduced in place of the oxide of zinc. A further variation in the
character of the liquid may be introduced by the use of medicated or
perfumed waters instead of the plain distilled water. Where so diluted,
as in the above formula, the yolk of egg separates out after long
standing, but the mixture quickly reëmulsifies upon shaking. Tar and
balsams can be emulsified by mixing with double their quantity of yolk
of egg, then diluting by the addition of small quantities of water or
milk.
«Emulgen.»—This emulsifying agent has the following composition:
Gluten, 5; gum acacia, 5; gum tragacanth, 20; glycerine, 20; water, 50;
alcohol, 10. This mixture forms a clear grayish jelly.
EMULSIONS OF PETROLEUM: See Petroleum.
«Enameling»
(See also Ceramics, Glazes, Paints, Waterproofing, and Varnishes.)
«COMMERCIAL ENAMELING.»
Commercial enameling includes: (1) Hollow ware enameling for domestic
use; (2) hollow ware enameling for chemical use; (3) enameling
locomotive and other tubes; (4) enameling drain and water pipes; (5)
signboard enameling.
There is one defect to which all enamel ware is subject, and that is
chipping. This may be caused by (1) imperfect mixing of the enamels;
(2) imperfect fusing; (3) imperfect pickling of the iron; (4) rough
usage. With ordinary care a well-enameled article has been known to
last in daily use for 10 or 12 years, whereas defective enameling,
say, on a sign tablet—which is exempt from rough usage—may not have
a life exceeding a few months. All enameled articles, such as hollow
ware and sign tablets, first receive a coating of a composition chiefly
composed of glass called “gray,” and this is followed by a deposit of
“white,” any additional color required being laid above the white.
In the mixing and depositing of these mixtures lie the secrets of
successful enameling. The “gray” has to be fused not only on but also
into the metal at a bright red—almost white—heat, and it is obvious
that its constituents must be arranged and proportioned to expand
and contract in a somewhat uniform manner with the iron itself. The
“white” has to be fused on the surface of the gray, but the gray being
much harder is not affected by the second firing. If it were liquid it
would become mixed with the white and destroy its purity. Frequently,
owing to inferior chemicals, imperfect mixing or fusing, a second
coating of white is necessary, in order to produce a surface of the
necessary purity and luster. The difficulties of enameling are thus
easily understood. Unless the metals and chemicals are so arranged and
manipulated that their capacities of expansion and contraction are
approximately the same, inferior work will be produced. Oxide of iron
on the surface of the plates, inferior chemicals, incorrect mixings,
insufficient or overheating in the process of fusing, prevent that
chemical combination which is essential to successful enameling. The
coatings will be laid on and not combined, with the result that there
will be inequalities in expansion and contraction which will cause the
enamel to chip off immediately if submitted to anything approaching
rough usage, and in a very short time if submitted to chemical or
ordinary atmospheric conditions.
The manufacture of sign tablets is the simplest form to which this
important art is adapted. Sign-tablet enameling is, however, kept as
great a secret as any other type. This branch of the industry {291} is
divided up as follows: (1) Setting the plates; (2) scaling and pickling
the plates; (3) mixing the enamel constituents; (4) melting the enamel
constituents; (5) grinding the enamel constituents; (6) applying the
enamel; (7) drying the enamel coatings; (8) fusing the enamel on the
articles; (9) lettering—including alphabetical and other drawing,
spacing, and artistic art in arrangement; (10) stencil cutting on paper
and stencil metal; (11) brushing; (12) refusing. Distinctive branches
of this work have distinctive experts, the arrangement being generally
as follows: Nos. 1 and 2 may or may not be combined; Nos. 3 and 5
may or may not be combined; Nos. 4, 7, 8, and 12 generally combined;
No. 6 generally the work of girls; Nos. 9 and 10 generally combined;
No. 11 generally the work of girls and boys. The twelve processes,
therefore, require six classes of trained workpeople, and incompetence
or carelessness at any section can only result in imperfect plates or
“wasters.”
A brief description of these processes will enable the reader to
understand the more detailed and technical description to follow, and
is, therefore, not out of place. Ordinary iron sheets will do for the
manufacture of sign tablets; but a specially prepared charcoal plate
can be had at a slightly increased price. The latter type is the
best, for in many cases the scaling and pickling may, to a certain
extent, be dispensed with. To make this article, however, as complete
as possible, we shall begin from the lowest rung of the manufacturing
ladder—i. e., from the first steps in the working of suitable iron.
I.—Setting.—The plates may be received in sheets, and cut to the
required size at the enameling factory, or, what is more general,
received in sizes according to specification. The former are more
liable to have buckled slightly or become dented, and have to be
restored to a smooth and uniform surface by hammering on a flat plate.
The operation seems simple, but an inexperienced operator may entirely
fail to produce the desired result, and, if he does succeed, it is
with the expenditure of a great amount of time. An expert setter with
comparatively few and well-directed strokes brings an imperfect plate
into truth and in readiness for the next operation.
II.—Scaling and Pickling.—The annealing of the sheets in special
furnaces loosens the scale, which can then be easily removed, after
which immersion for some time in diluted sulphuric or muriatic acid
thoroughly cleans the plate. Firing to a red heat follows, and then a
generous course of scrubbing, and the last traces of acid are removed
by dipping in boiling soda solution. Scouring with sand and washing in
clean water may follow, and the metal has then a perfect and chemically
clean surface.
III.—Mixing the Enamel Constituents.—Ground, foundation, or gray.—All
articles, whether hollow ware or plates, are operated upon in a
very similar manner. Both require the foundation coating generally
called “gray.” The gray constituents vary considerably in different
manufactures; but as regards the use of lead, it is universally
conceded that while it may in many instances be used with advantage in
the enameling of sign tablets, etc., it should under no circumstances
be introduced into the coating of articles for culinary purposes, or in
which acids are to be used. The first successful commercial composition
of this covering was: Cullet (broken glass), carbonate of soda, and
boracic acid. This composition remained constant for many years, but
ultimately gave place to the following: Cullet, red lead, borax, niter.
The borax and red lead form the fluxes, while the niter is to “purify”
the mass. Some of the later mixings consist of the following: Silica
powder, crystallized or calcium borax, white lead, fused together.
This would be called a frit, and with it should be pulverized powdered
silica, clay, magnesia. This recipe is one requiring a very high
temperature for fusing: Silica powder, borax, fused and ground with
silica, clay, magnesia. This requires a slightly lower temperature:
Frit of silica powder, borax, feldspar, fused together, and then ground
with clay, feldspar, and magnesia.
The approximate quantities of each constituent will be given later,
but it must always be remembered that no hard-and-fast line can be
laid down. Chemicals vary in purity, the furnaces vary in temperature,
the pounding, grinding, and mixing are not always done alike, and each
of these exerts a certain influence on the character of the “melt.”
These compositions may be applied to the metal either in the form of
a powder or of a liquid. Some few years ago the powder coating was in
general use, but at the present time the liquid form is in favor, as
it is considered easier of application, capable of giving a coating
more uniform in thickness and less costly. In using the powder coating
the plate is rubbed with a cloth dipped in a gum {292} solution, and
the powder then carefully dusted through a sieve over the surface. In
this condition the plate is submitted to the fusing process. In using
the liquid material the plate surface is dipped into or has the liquid
mixing carefully poured over it, any surplus being drained off, and
any parts which are not to be coated being wiped clean by a cloth. The
coating is then dried in suitable stoves, after which it is ready for
fusing on to the iron. The gray coating should be fairly uniform and
smooth, free from holes or blisters, and thoroughly covering every part
of the iron which is to be subjected to any outside influence. Cooling
slowly is important. Rapid cooling frequently causes chipping of the
coating, and in any case it will greatly reduce the tenacity of the
connection existing between the glaze and the metal.
Generally the next surface is a white one, and it depends upon the
class of article, the character of the enamels, and the efficiency
of application, whether one coat or two will be required. Roughly
speaking, the coating is composed of a glass to which is added oxide of
tin, oxide of lead, or some other suitable opaque white chemical. The
mixture must be so constituted as to fuse at a lower temperature than
the foundation covering. If its temperature of fusion were the same
the result would be that the gray would melt on the iron and become
incorporated with the white, thus loosening the attachment of the mass
to the iron and also destroying the purity of the white itself. Bone
ash is sometimes used, as it becomes uniformly distributed throughout
the melt, and remains in suspension instead of settling. Bone ash and
oxide of lead are, however, in much less demand than oxide of tin. The
lead is especially falling into disfavor, for the following reasons:
Firstly, it requires special and laborious treatment; secondly, it
gives a yellowish-white color; thirdly, it cannot resist the action
of acids. The following is a recipe which was in very general use for
some years: Glass (cullet), powdered flint, lead, soda (crystals),
niter, arsenic. Another consists of the following: Borax, glass, silica
powder, oxide of tin, niter, soda, magnesia, clay. These are fused
together, and when being ground a mixture of Nos. 1, 3, 7, and boracic
acid is added.
Enamel mixings containing glass or china are now generally in use,
although for several years the experience of manufacturers using glass
was not satisfactory. Improved compositions and working now make this
constituent a most useful, and, in fact, an almost essential element.
The glass should be white broken glass, and as uniform in character as
possible, as colored glass would impart a tinge of its own color to the
mixing.
The following are two distinct glazes which do not contain glass or
porcelain: Feldspar, oxide of tin, niter, soda. This is free from any
poisonous body and requires no additions: Silica powder, oxide of tin,
borax, soda, niter, carbonate of ammonia, or magnesia.
Alkalies.—Of the alkalies which are necessary to produce complete
fusion of and combination with the quartz, soda is chiefly applied in
enamel manufactures, as the fusing temperature is then lower.
Bone Ash.—This material will not add opacity, but only
semi-transparency to the enamel, and is therefore not much used.
Boracic Acid.—Boracic acid is sometimes substituted for silicic acid,
but generally about 15 per cent of the former to 85 per cent of the
latter is added. Borax as a flux is, however, much more easily used and
is therefore largely employed in enamel factories.
Borax.—Calcined borax, that is, borax from which a large proportion of
the natural moisture has been eliminated, is best for enamel purposes.
It is a flux that melts at medium heat, and enters into the formation
of the vitreous basis. Borax has also the property of thoroughly
distributing oxide colors in the enamels.
Clay.—Only a fairly pure clay can be used in enamel mixings, and the
varieties of clay available are therefore limited. The two best are
pipe—or white—clay and china clay—kaolin. The latter is purer than the
former, and in addition to acting as a flux, it is used to increase the
viscosity of mixings and therefore the opacity. It is used in much the
same way as oxide of tin.
Cryolite.—Ground cryolite is a white mineral, easily fusible, and
sometimes used in enamel mixings. It is closely associated with
aluminum.
Cullet.—This is the general material used as a basis. Clear glass only
should be introduced; and as the compositions of glass vary greatly,
small experimental frits should always be made to arrive at the correct
quantity to be added.
Feldspar.—The introduction of feldspar into an enamel frit increases
consistency. The common white variety is {293} generally used, and
its preliminary treatment by pounding is similar to that adopted with
quartz.
Fluor-Spar.—In this mineral we have another flux, which fuses at a red
heat.
Fluxes.—These are for the purpose of regulating the temperature of
fusion of a mixing—frit—some being better adapted for this purpose than
others. This, however, is not the only consideration, for the character
of the flux depends upon the composition or chemical changes to which
the ingredients are to be subjected. The fluxes are borax, clays,
cullet, porcelain, feldspar, gypsum, and fluorspar.
Glass.—Glass is composed of lime, silicic acid, and soda or potash. The
use of the glass is to form the hard, crystal-like foundation.
Gypsum.—This mineral is sometimes used in conjunction with baryta and
fluor-spar.
Lead.—Crystallized carbonate of lead, or “lead white,” is frequently
used in enamels when a low temperature for fusion is required. It
should never be used on articles to be submitted to chemical action,
or for culinary use. Minium is a specially prepared oxide of lead, and
suitable for enameling purposes, but is expensive.
Lime.—Lime is in the form of carbonate of calcium when used.
Magnesium Carbonate is used only in small quantities in enamel mixings.
It necessitates a higher temperature for fusion, but does not affect
the color to the slightest extent if pure.
Manganese.—As a decolorant, this mineral is very powerful, and
therefore only small quantities must be used. Purity of the mineral is
essential—i. e., it should contain from 95 to 98 per cent of binoxide
of manganese.
Niter.—At a certain temperature niter shows a chemical change, which,
when affected by some of the other constituents, assists in the
formation of the vitreous base.
Porcelain.—Broken uncolored porcelain is sometimes used in enamel
manufacture. Its composition: Quartz, china clay, and feldspar. It
increases viscosity.
Red Lead.—This decolorant is sometimes called purifier. It will,
however, interfere with certain coloring media, and when this is the
case its use should at once be discontinued.
Silicic Acid.—Quartz, sand, rock crystal, and flint stone are all
forms of this acid in crystallized form. By itself it is practically
infusible, but it can be incorporated with other materials to form
mixings requiring varying temperatures for fusion.
Soda.—The soda in general use is carbonate of soda—58 per cent—or
enameling soda. The latter is specially prepared, so as to free it
almost entirely from iron, and admit of the production of a pure white
enamel when such is required.
Tin Oxide.—All enamels must contain white ingredients to produce
opacity, and the most generally used is oxide of tin. By itself it
cannot be fused, but with proper manipulation it becomes diffused
throughout the enamel mass. On the quantity added depends the denseness
or degree of opacity imparted to the enamel.
It will be understood that the enamel constituents are divided into
four distinct groups: I. Fundamental media. II. Flux media. III.
Decolorant media. IV. Coloring media. We have briefly considered the
three first named, and we will now proceed to No. IV. The coloring
material used is in every case a metallic oxide, so that, so far
as this goes, the coloring of an enamel frit is easy enough. Great
care is, however, necessary, and at times many difficulties present
themselves, which can only be overcome by experience. Coloring oxides
are very frequently adulterated, and certain kinds of the adulterants
are injurious to the frit and to the finish of the color.
«Comparison of Hollow Ware and Sign-Tablet Enameling.»—The enameling
for sign tablets is much the same as for hollow ware; the mixings are
practically alike, but, as a general rule, the mixing is applied in
a much more liquid form on the latter. It is easy to understand that
hollow ware in everyday use receives rougher usage than tablets. By
handling, it is submitted to compression, expansion, and more or less
violence due to falls, knocks, etc., and unless, therefore, the enamel
coating follows the changes of the metal due to these causes, the
connection between the two will become loosened and chipping will take
place.
The enamel, therefore, though much alike for both purposes, should be
so prepared for hollow ware that it will be capable of withstanding the
changes to which we have referred. In all cases it must be remembered
that the thinner the coat of the enamel the better it will be {294}
distributed over the iron, and the greater will be its adherence to
the iron. Any article heavily enameled is always liable to chip,
especially if submitted to the slightest bending action, and therefore
any excess of material added to a plate means that it will always be
readily liable to separate from the plate. In hollow-ware enameling the
preparation of each frit generally receives somewhat more attention
than for plate enameling. The grinding is more effectively carried out,
in order to remove almost every possibility of roughness on any part of
the surface, especially the inside surface.
The iron used in tablet and hollow-ware manufacture is rolled sheet
iron. It is supplied in a variety of qualities. Charcoal iron is purer
than ordinary plate iron, more ductile, and therefore capable of
being driven out to various forms and depths by stamping presses. The
surface of the charcoal iron is not so liable to become oxidized, and
therefore can be more readily made chemically clean for the reception
of the enamels. Some manufacturers use charcoal plates for tablet work,
but these are expensive; the ordinary plates, carefully pickled and
cleaned, adapt themselves to the work satisfactorily.
The sheet irons generally used for the enameling purposes referred to
vary in gauge. The finer the iron the greater must be the care used in
coating it with enamel. Thin iron will rapidly become hot or cool, the
temperatures changing much more quickly than that of the mixing. Unless
care, therefore, is used, the result of fusing will be that the enamel
mass will not have become thoroughly liquid, and its adherence to the
iron will be imperfect.
If, however, the temperature is gradually raised to the maximum, and
sympathetic combination takes place, the dangers of rapid cooling are
avoided. Again, the iron, in losing its temperature more rapidly than
the enamel, will contract, thus loosening its contact with the glaze,
and the latter will either then, or after a short period of usage,
chip off. We then arrive at the following hard-and-fast rules: (1) In
all classes of enameling, but particularly where thin iron sheets are
used, the temperature of the plate and its covering must be raised very
gradually and very uniformly. (2) In all cases a plate which has had
a glaze fused on its surface must be cooled very gradually and very
uniformly. The importance of these rules cannot be over-estimated, and
will, therefore, be referred to in a more practical way later.
In enameling factories no causes are more prolific in the production
of waste than these, and in many cases the defects produced are
erroneously attributed to something else. Cast iron is much easier to
enamel than wrought iron. This is due to the granular character of its
composition. It retains the enamels in its small microscopic recesses,
and greater uniformity can be arrived at with greater ease. Cast-iron
enameled sign tablets and hollow ware were at one time made, but their
great weight made it impossible for them ever to come into general use.
Wrought-iron plates, if examined microscopically, will show that they
are of a fibrous structure, the fibers running in the direction in
which they have been rolled. The enamels, therefore, will be more
liable to flow longitudinally than transversely, and this tendency
will be more accentuated at some places than at others. This, however,
is prevented by giving the iron sheets what might be described as
a cast-iron finish. The sheets to be enameled should be thoroughly
scoured in all directions by quartz or flint sand, no part of the
surface being neglected. This thorough scrubbing will roughen the
surface sufficiently to make it uniformly retentive of enamel mixture,
and in no cases should it be omitted or carelessly carried out.
«Copper Enameling.»—On a clean copper surface the enameling process
is easy. The foundation glaze is not essential, and when required the
most beautiful results of blended colors can be obtained by very little
additional experience to ordinary enameling.