off to the fullest extent, there may still be unnecessary waste.
The arrangement of the bars should only be made by those who fully
understand the character of the coal and the objects in view. The
fireman in charge should be thoroughly experienced and reliable, as
much waste is frequently traced to imperfect feeding of the fuel.
Each charge of articles should be as large as possible, as fusing will
take place equally as well on many articles as on few. The charges
should follow one another as rapidly as can be conveniently carried
out; and where this is not done there is a lack of organization which
should be immediately remedied.
[Illustration: GRINDING MILL
Fig. 9]
«Mills.»—Any hard substances must first be broken up and pounded in
a pounding or stamping mill, or in any other suitable manner, thus
reducing the lumps to a granular condition. When this has been done,
the coarse is separated from the fine parts and the former again
operated on. The next process is roller grinding for reducing the
hard fritted granular particles to a fine powder. These mills vary
in construction, but a satisfactory type is shown in Fig. 9. Motion
is conveyed by a belt to the driving pulley, and this is transmitted
from the pinion to the large bevel, which is connected by a shaft to
the ground plate. As this revolves the material causes the mill wheels
to revolve, and in this way the material is reduced to a powder. The
rollers are of reduced diameter on the inner side to prevent slippage,
and when all the parts are made of iron, the metal must be close
grained and of very hard structure, so as to reduce the amount removed
by wear to a minimum. When the materials are ground wet, the powder
should be carefully protected from dust and thoroughly dried before
passing to the next operation.
[Illustration: GLAZING MILL
Fig. 10]
The glazing or enamel mills are shown in Fig. 10. These mills consist
of a strong iron frame securely bolted to a stone foundation. In the
sketch shown the framing carries 2 mills, but 3 or 4 can be arranged
for. A common arrangement for small factories consists of 2 large
mills, and 1 smaller mill, driven from the same shaft. One of the mills
is used for foundation or gray mixings, the second for white, and the
smallest one for colored mixings. In these mills it is essential that
the construction is such as to prevent any iron fitting coming into
contact with the mixing, for, as has already been explained, the iron
will cause discoloration. The ground plate is composed of quartz and
is immovable. It is surrounded by a wooden casing—as shown at _a_—and
bound together by iron hoops. The millstones are heavy, rectangular
blocks of quartz, called “French burr stone,” and into the center the
spindle, _b_, is led. The powdered material mixed with about three
times its bulk of water is poured into the vats, _a_, and the grinding
stones are then set in motion. When a condition ready for enameling
has been reached the mixture is run off through the valves, _c_. Each
mill can be thrown out of gear when required, by means of a clutch box,
without interfering with the working of the others. The grinding stones
wear rapidly and require to be refaced from time to time. To avoid
stoppage of the work, therefore, it is advisable to always have a spare
set in readiness to replace those removed for refacing. The composition
of the stones should not be neglected, for, in many cases, faults in
the enamel have been traced to the wearing away of stones containing
earthy or metallic matter. {302}
«Enamel Mixing.»—All constituents of which an enamel glaze is composed
must be intimately mixed together. This can only be done by reducing
each to a fine powder and thoroughly stirring them up together. This
part of the work is often carried out in a very superficial manner, one
material showing much larger lumps than another. Under circumstances
such as these it is absurd to imagine that in fusion equal distribution
will take place. What really happens is that some parts of the mass
are insufficiently supplied with certain properties while others have
too much. A mixture of this class can produce only unsatisfactory
results in every respect, for the variations referred to will produce
variations in the completeness of fusion in the viscous character of
the mass, and in the color.
The mixing can be done by thoroughly stirring the various ingredients
together, and a much better and cheaper system is mixing in rotating
barrels or churns. These are mounted on axles which rest in bearings,
one axle being long enough to carry a pulley. From the driving shaft a
belt is led to the cask, which then rotates at a speed of from 40 to 60
revolutions per minute, and in about a quarter of an hour the operation
is complete. The cask should not exceed the 5-gallon size, and should
at no time be more than two-thirds full. Two casks of this kind give
better results than one twice the size. The materials are shot into the
cask in their correct proportions through a large bung hole, which is
then closed over by a close-fitting lid.
«Mixings.»—For gray or fundamental coatings:
I.—Almost any kind of glass 49 per cent
Oxide of lead 47 per cent
Fused borax 4 per cent
II.—Glass (any kind) 61 per cent
Red lead 22 per cent
Borax 16 per cent
Niter 1 per cent
III.—Quartz 67.5 per cent
Borax 29.5 per cent
Soda (enameling) 3 per cent
The above is specially adapted for iron pipes.
IV.—Frit of silica powder 60 per cent
Borax 33 per cent
White lead 7 per cent
Fused and then ground with—
Three-tenths weight of silica frit.
Clay, three-tenths weight of silica frit.
Magnesia, one-sixth weight of white lead.
V.—Silica 65 per cent
Borax 14 per cent
Oxide of lead 4 per cent
Clay 15 per cent
Magnesia 2 per cent
No. V gives a fair average of several mixings which are in use, but it
can be varied slightly to suit different conditions of work.
«Defects in the Gray or Ground Coating.»—Chipping is the most
disastrous. This may be prevented by the addition of some bitter salt,
say from 3 to 4 per cent of the weight of the frit.
The addition of magnesia when it has been omitted from the frit may
also act as a preventive, but it should only be added in very small
quantities, not exceeding 2.5 per cent, otherwise the temperature
required for fusion will be very great.
«Coating and Fusion.»—Difficulties of either may generally be done away
with by reducing the magnesia used in the frit to a minimum.
A soft surface is always the outcome of a mixing which can be fused at
a low temperature. It is due to too much lead or an insufficiency of
clay or silica powder.
A hard surface is due to the quantity of lead in the mixing being too
small. Increase the quantity and introduce potash, say about 2.5 per
cent.
The gray or fundamental mixing should be kept together in a condition
only just sufficiently liquid to allow of being poured out. When
required to be applied to the plate, the water necessary to lower it to
the consistency of thick cream can then be added gradually, energetic
stirring of the mass taking place simultaneously in order to obtain
uniform distribution.
The time required for fusion may vary from 15 minutes to 25 minutes,
but should never exceed the latter. If it does, it shows that the
mixing is too viscous, and the remedy would be the addition and
thorough intermixture of calcined borax or boracic acid. Should this
fail, then remelting or a new frit is necessary.
A highly glazed surface on leaving the muffle shows that the
composition is too fluid and requires the addition of clay, glass,
silica powder or other substance to increase the viscosity.
As has been already explained, the glaze is much more important than
the fundamental coating. Discoloration or slight flaws which could be
tolerated in the latter would be fatal to the former. {303}
In glazes, oxide of lead need not be used. It should never be used in
a coating for vessels which are to contain acids or be used as cooking
utensils. It may be used in sign-tablet production.
For pipes the following glaze gives good results:
I.—Feldspar 33 per cent
Borax 22.5 per cent
Quartz 16.5 per cent
Oxide of tin 15 per cent
Soda 8 per cent
Fluorspar 3.75 per cent
Saltpeter 2.25 per cent
For sign tablets the following gives fair results, although some of the
succeeding ones are in more general use:
II.—Cullet 20 per cent
Powdered flint 15 per cent
Lead 52 per cent
Soda 4.5 per cent
Arsenic 4.5 per cent
Niter 4 per cent
III.—Frit of silica powder 30 per cent
Oxide of tin 18 per cent
Borax 17 per cent
Soda 8.6 per cent
Niter 7.5 per cent
White lead 5.5 per cent
Carbonate of ammonia 5.5 per cent
Magnesia 4 per cent
Silica powder 4 per cent
The following are useful for culinary utensils, as they do not contain
lead:
IV.—Frit of silica powder 26 per cent
Oxide of tin 21 per cent
Borax 20 per cent
Soda 10.25 per cent
Niter 7 per cent
Carbonate of ammonia 5 per cent
Magnesia 3.25 per cent
This should be ground up with the following:
Silica powder 4.25 per cent
Oxide of tin 2.25 per cent
Soda 0.5 per cent
Magnesia 0.5 per cent
V.—Feldspar 41 per cent
Borax 35 per cent
Oxide of tin 17 per cent
Niter 7 per cent
VI.—Borax 30 per cent
Feldspar 22 per cent
Silicate powder 17.5 per cent
Oxide of tin 15 per cent
Soda 13.5 per cent
Niter 2 per cent
Borax will assist fusion. Quartz mixings require more soda than
feldspar mixings.
VII.—Borax 28 per cent
Oxide of tin 19.5 per cent
Cullet (powdered white glass) 18 per cent
Silica powder 17.5 per cent
Niter 9.5 per cent
Magnesia 5 per cent
Clay 2.5 per cent
VIII.—Borax 26.75 per cent
Cullet 19 per cent
Silica powder 18.5 per cent
Oxide of tin 19 per cent
Niter 9.25 per cent
Magnesia 4.5 per cent
Soda 3 per cent
To No. VII must be added—while being ground—the following percentages
of the weight of the frit:
Silica powder 18 per cent
Borax 9 per cent
Magnesia 5.25 per cent
Boracic acid 1.5 per cent
To No. VIII should be similarly added the following percentages of the
frit:
Silica powder 1.75 per cent
Magnesia 1.75 per cent
Soda 1 per cent
This mixing is one which is used in the production of some of the best
types of hollow ware for culinary purposes. The glaze should be kept in
tubs mixed with water until used, and it should be carefully protected
from dust.
«Defects in the Glaze or White.»—A bad white may be due to its being
insufficiently opaque. More oxide of tin is required. Cracks may
be prevented by the addition of carbonate of ammonia. Insufficient
luster can be avoided by adding to the quantity of soda and reducing
the borax. If the gray shows through the white it proves that the
temperature of fusion is too high or the viscosity of the mixing is
too great. If the coating is not uniformly spread it may be due to the
glaze being too thin; add magnesia. If the glaze separates from the
gray add some bitter salt. Viscosity will be increased by reducing the
quantity of borax. Immunity against chemical reaction is procured by
increasing the quantity of borax. An improved luster will be obtained
by adding native carbonate of soda. The greater the quantity of silicic
acid the greater must be the temperature for fusion. To reduce the
temperature add borax. Clay will increase the difficulty {304} of
fusion. Oxide of lead will make a frit more easily fusible. A purer
white can be obtained by adding a small quantity of smalt.
«Water.»—The character of the water used in the mixing of enamels is
too frequently taken for granted, for unsuitable water may render a
mixing almost entirely useless. Clean water, and with little or no
sulphur present, is essential. For very fine enamels it is advisable
to use carefully filtered water which has shown, after analysis, that
it is free from any matter which is injurious to any of the enamel
constituents.
«How to Tell the Character of Enamel.»—In the case of sign tablets
the characteristics looked to are appearance and the adherence of
the coatings to the iron. For the latter the tests are simple. The
plate if slightly bent should not crack the coating. An enamel plate
placed in boiling water for some time and then plunged into very cold
water should not show any cracks, however small, even after repeated
treatment of this kind.
Culinary utensils, and those to hold chemicals, should not only look
well, but should be capable of resisting the action of acids. Lead
should never enter into the composition of enamels of this class, as
they then become easily acted upon, and in the case of chipping present
a menace to health. The presence of lead is easily detected. Destroy
the outside coating of the enamel at some spot by the application
of strong nitric acid. Wash the part and apply a drop of ammonium
sulphide. If lead is present, the part will become almost black, but
remains unchanged in color if it is absent.
Another simple test is to switch up an egg in a vessel and allow it
to stand for about 24 hours. When poured out and rinsed with water a
dark stain will remain if lead is present in the enamel. To test the
power of chemical resistance is equally simple. Boil diluted vinegar
in the vessel for several minutes, and if a sediment is formed and the
luster and smoothness of the glaze destroyed or partially destroyed, it
follows that it is incapable of resisting the attacks of acids for any
length of time. There are several other tests adopted, but those given
present little difficulty in carrying out, and give reliable results.
«Wasters and Seconds: Repairing Old Articles.»—In all enameling there
must be certain articles turned out which are defective, but the
percentage should never be very great. The causes which most frequently
tend to the production of wasters are new mixings and a temperature
of fusion which is either too high or too low. There are two ways of
disposing of defective articles, viz.: (1) Chipping off the bad spots,
patching them up and selling them as “seconds”; (2) throwing the
articles into the waste heap. The best firms adopt the latter course,
because the recoating and firing of defective parts practically means a
repetition of the whole process, thus adding greatly to the cost, while
the selling price is reduced. Overheating in fusion is generally shown
by blisters or by the enamel being too thin in various places. Chipping
may be also due to this cause, the excessive heat having practically
fused the fundamental coating.
At this stage the defects may be remedied by breaking off the faulty
parts, patching them up, and then recoating the whole. With sign
tablets there is no objection to doing so, but with hollow ware the
fact remains that the article is faulty, no matter how carefully
defects may be hidden. As white is the most general coating used, and
shows up the defects more than the colored coatings, the greatest
care is necessary at every stage of the manufacture. While glowing
on the article, it should appear uniformly yellow, but on cooling it
should revert to a pure white shade. On examining different makes
of white coated articles, it will be found that some are more opaque
than others. The former are less durable than the latter, because
they contain a large percentage of oxide of tin, which reduces the
elasticity. To ensure hardness the mixing must be very liquid, and
this cannot be arrived at when a large quantity of oxide of tin is
introduced.
Old utensils which have become broken or chipped can be repaired,
although, except in the case of large articles, this is rarely done.
The operations necessary are: (1) The defective parts chipped off; (2)
submitted to a red heat for a few moments; (3) coated with gray on the
exposed iron; (4) fused; (5) coated with the glaze on the gray; (6)
fused.
«To Repair Enameled Signs.»—
Copal 5 parts
Damar 5 parts
Venice turpentine 4 parts
Powder the rosins, mix with the turpentine and add enough alcohol
to form a thick liquid. To this add finely powdered zinc white in
sufficient quantity to yield a plastic mass. Coloring {305} matter may,
of course, be added if desired.
The mass after application is polished when it has become sufficiently
hard.
«Enamel for Copper Cooking Vessels.»—White fluorspar is ground to a
fine powder and strongly calcined with an equal volume of unburnt
gypsum, at a light glowing heat, stirring diligently. Grind the mixture
to a paste with water, paint the vessel with it, using a brush, or
pour in the paste like a glaze and dry the same. Increase the heat
gradually and bring the vessels with the glass substance quickly into
strong heat, under a suitable covering or a mantle of burnt clay. The
substance soon forms a white opaque enamel, which adheres firmly to the
copper. It can stand pretty hard knocks without cracking, is adapted
for cooking purposes and not attacked by acid matters. If the glassy
substance is desired to cling well and firmly to the copper, a sudden
and severe heat must be observed.
«To Pickle Black Iron-Plate Scrap Before Enameling.»—The black
iron-plate scraps are first dipped clean in a mixture of about 1 part
of sulphuric acid and 20 to 22 parts of water heated to 30° to 40° C.
(86° to 104° F.), and sharp quartz sand is then used for scouring. They
are then plunged for a few seconds in boiling water, taken out, and
allowed to dry. Rinsing with cold water and allowing to dry thus may
cause rust. The grains of quartz cut grooves in the fibers of the iron;
this helps the grounding to adhere well. With many kinds of plate it
is advisable to anneal after pickling, shutting off the air; by this
means the plates will be thoroughly clean and free from oxidation. Much
practice is required.—_The Engineer._
«ENAMELED IRON RECIPES.»
The first thing is to produce a flux to fuse at a moderate heat, which,
by flowing upon the plate, forms a uniform surface for the white or
colored enamels to work upon.
Flux for Enameled Iron.—
White lead 10 parts
Ball clay 1 part
Flint glass 10 parts
Whiting 1 part
The plates may then be coated with any of the following mixtures, which
may either be spread on as a powder with a little gum, as in the case
of the flux, or the colors may be mixed with oil and the plates dipped
therein when coated; the plate requires heating sufficiently to run the
enamels bright.
Soft Enamels for Iron, White.—
Flint glass 16 parts
Oxide of tin 1 1/2 parts
Niter 1 1/2 parts
Red lead 4 parts
Flint or china clay 1 part
Black.—
Red oxide of iron 1 1/4 parts
Carbonate of cobalt 1 1/4 parts
Red lead 6 parts
Borax 2 parts
Lynn sand 2 parts
Yellow Coral.—
Chromate of lead 1 part
Red lead 2 3/4 parts
Flint 1 part
Borax 1/4 part
Canary.—
Oxide of uranium 1 part
Red lead 4 1/2 parts
Flint 1 1/2 parts
Flint glass 1 part
Turquoise.—
Red lead 40 parts
Flint glass 12 parts
Borax 16 parts
Flint 12 parts
Enamel white 14 parts
Oxide of copper 7 parts
Oxide of cobalt 1/4 part
Red Brown.—
Calcined sulphate of iron 1 part
Flux No. 8 (see page 307) 3 parts
Mazarine Blue.—
Oxide of cobalt 10 parts
Paris white 9 parts
Sulphate barytes 1 part
Fire the above at an intense heat and for use take
Above stain 1 part
Flux No. 8 (see page 307) 3 parts
Sky Blue.—
Flint glass 30 parts
White lead 10 parts
Pearlash 2 parts
Common salt 2 parts
Oxide of cobalt 4 parts
Enamel, white 4 parts
Chrome Green.—
Borax 10 parts
Oxide of chrome 4 1/2 parts
White lead 9 parts
Flint glass 9 parts
Oxide of cobalt 2 parts
Oxide of tin 1 part {306}
Coral Red.—
Bichromate potash 1 part
Red lead 4 1/2 parts
Sugar of lead 1 1/2 parts
Flint 1 1/2 parts
Flint glass 1 part
Enamel White.—Soft:
Red lead 80 parts
Opal glass 50 parts
Flint 50 parts
Borax 24 parts
Arsenic 8 parts
Niter 6 parts
Enamel White.—
Red lead 10 parts
Flint 6 parts
Boracic acid 4 parts
Niter 1 part
Soda crystals 1 part
Where the enameled work is intended to be exposed to the weather do not
use flux No. 8, but substitute the following:
White lead 1 part
Ground flint glass 1 part
All the enamels should, after being mixed, be melted in crucibles,
poured out when in liquid, and powdered or ground for use.
«FUSIBLE ENAMEL COLORS.»
The following colors are fusible by heat, and are all suitable for the
decoration of china and glass. In the following collection of recipes
certain terms are employed which may not be quite understood by persons
who are not connected with either the glass or porcelain industries,
such as “glost fire” and “run down,” and in such cases reference must
be made to the following definitions:
“Run down.” Sufficient heat to melt into liquid.
“Glost fire.” Ordinary glaze heat.
“Grind only.” No calcination required.
“Hard fire.” Highest heat attainable.
“Frit.” The ingredients partly composing a glaze, which require
calcination.
“Stone.” Always best Cornwall stone.
“Paris white.” Superior quality of whiting.
“Parts.” Always so many parts _by weight_, unless otherwise stated.
“D. L. Zinc.” Particular brand not essential. Any good quality oxide of
zinc will do.
Ruby and Maroon.—Preparation of silver:
Nitric acid 1 ounce
Water 1 ounce
Dissolve the silver till saturated, then put a plate of copper in the
solution to precipitate the silver in a metallic state. Wash well with
water to remove the acetate of copper.
Flux for Above.—Six dwts. white lead to 1 ounce prepared silver.
Tin Solution.—Put the acid (aqua regia) in a bottle, add tin in small
quantities until it becomes a dark-red color; let it stand about 4 days
before use. When the acid becomes saturated it will turn red at the
bottom of the bottle, then shake it up and add more tin; let it stand
and it will become clear.
Aqua Regia.—
Nitric acid 2 parts
Muriatic acid 1 part
Dissolve grain gold in the aqua regia so as to make a saturated
solution. Take a basin and fill it 3 parts full of water; drop the
solution of gold into it till it becomes an amber color. Into this
solution of gold gradually drop the solution of tin, until the
precipitate is complete. Wash the precipitate until the water becomes
tasteless, then dry slowly and flux as follows:
Flux No. I.—
Borax 3 parts
Red lead 3 parts
Flint 2 parts
Run down.
Rose Mixture.—
Purple of Cassius 1 ounce
Flux No. 1 6 ounces
Prepared silver 3 dwts.
Flint glass 2 ounces
Grind.
Purple Mixture.—
Purple of Cassius 1 ounce
Flux No. 8 (see page 307) 2 1/2 ounces
Flint glass 2 ounces
Grind.
Ruby.—
Purple mixture 2 1/2 parts
Rose mixture 1 1/2 parts
Grind.
Maroon.—
Rose mixture 1 part
Purple mixture 2 parts
Grind. {307}
Black—Extra quality.—
Red oxide of iron 12 parts
Carbonate of cobalt 12 parts
Oxide of cobalt 1 part
Black flux A (see next formula) 80 parts
Glost fire.
Black Flux A.—
Red lead 3 parts
Calcined borax 1/2 part
Lynn sand 1 part
Run down.
Black No. 2.—
Oxide of copper 1 part
Carbonate of cobalt 1/2 part
Flux No. 8 (see next column) 4 parts
Grind only.
Enamel White.—
Arsenic 2 1/2 parts
Niter 1 1/2 parts
Borax 4 parts
Flint 16 parts
Glass 16 parts
Red lead 32 parts
Glost fire.
Turquoise.—China:
Calcined copper 5 parts
Whiting 5 parts
Phosphate of soda 8 parts
Oxide of zinc 16 parts
Soda crystals 4 parts
Magnesia 2 parts
Red lead 8 parts
Flux T (see next formula) 52 parts
Glost fire.
Flux T.—
Borax 2 parts
Sand 1 part
Run down.
Orange.—
Orange U. G. 1 part
Flux No. 8 (see next column) 3 parts
Grind only.
Blue Green.—
Flint glass 8 parts
Enamel white 25 parts
Borax 8 parts
Red lead 24 parts
Flint 6 parts
Oxide of copper 2 1/2 parts
Glost heat.
Coral Red.—
Chromate of potash 1 part
Sugar of lead 1 1/2 parts
Dissolve in hot water, then dry. Take 1 part of above, 3 parts flux for
coral. Grind.
Flux for Coral.—
Red lead 4 1/2 parts
Flint 1 1/2 parts
Flint glass 1 1/2 parts
Run down.
Turquoise.—
Oxide of copper 5 parts
Borax 10 parts
Flint 12 parts
Enamel white 14 parts
Red lead 40 parts
Glost fire.
Flux No. 8.—
Red lead 6 parts
Borax 4 parts
Flint 2 parts
Run down.
Russian Green.—
Malachite green 10 parts
Enamel yellow 5 parts
Majolica white 5 parts
Flux No. 8 (see previous formula) 2 parts
Grind only.
Amber.—
Oxide of uranium 1 part
Coral flux 8 parts
Grind only.
Gordon Green.—
Yellow U. G. 5 parts
Flux No. 8 (see above) 15 parts
Malachite green 10 parts
Grind only.
Celadon.—
Enamel light blue 1 part
Malachite green 1 part
Flux No. 8 (see above) 15 parts
Grind only.
Red Brown.—
Sulphate of iron, fired 1 part
Flux No. 8 (see above) 3 parts
Grind only.
Matt Blue.—
Flux No. 8 (see above) 10 1/2 parts
Oxide of zinc 5 parts
Oxide of cobalt 4 parts
Glost fire, then take
Of above base 1 part
Flux No. 8 (see above) 1 1/8 parts
Grind only. {308}
«PREPARATION OF ENAMELS.»