Read Ebook: How to Enamel Being a Treatise on the Practical Enameling of Jewelry with Hard Enamels by Chapin Howard M

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A blend between two colors may be obtained by mixing two enamels together and then charging the piece with the mixture. Such a mixture when fired is often found to be speckled instead of a clear shade. If, after mixing, the enamel is ground finer, this speckled effect can sometimes be eliminated. This process is by no means always satisfactory.

With most transparent colors it is desirable, though not necessary except in the case of so-called "opals," to use an under layer of fondant, that is, on the first charging, to cover the entire surface with a thin layer of transparent white or colorless enamel, commonly called flux or fondant. This under layer of fondant is used more on gold than on silver or copper, but in any case it will greatly enhance the brilliancy of the enamels. It is of great assistance in bringing out delicate colors and especially "opals," for if opals are charged directly upon the stock they have a strong tendency to become opaque when fired. Some delicate roses and pinks if put directly upon the metal will "fire" black, while over a layer of fondant they became beautiful and delicate shades.

Where several colors are used on the same piece it is generally advantageous to use fondant for the last layer. The advantage of this is that the harmony and qualities of the different colors are then not affected by the stoning and polishing, which no matter how carefully done are bound to cut down the enamel, and in the case of transparent colors the thinner a layer becomes the lighter it becomes.

Any transparent color can be made lighter either by being stoned down or by being put on over a layer of fondant. Transparent white can easily be obtained on silver by the use of bluish and white fondants, but it is impossible to obtain transparent white on gold or copper unless these metals are first plated with silver.

Most enamels appear to best advantage on silver over fondant, and when the same enamel is put on another metal it changes its hue. This change of hue varies with each individual enamel and can only be learned by experiment. In general, white on silver becomes pink on gold or copper, orange becomes red, yellow becomes orange or brown, blue has a tendency to green and green to yellow. Opaque colors of course do not actually change color, but owing to the different color of their setting they often give different effects.

Some shades that cannot be obtained by mechanically mixing opaque colors or by layers of different transparent colors, can be obtained by putting a layer of transparent enamel over a layer of opaque. Opaque white as an under layer will often give a desirable shade to a transparent enamel which is not just the color required.

FIRING

AFTER enamel has been charged on a piece of metal, it is "fired," that is, heated until the enamel is fused, after which, on cooling, it becomes hard. It is best fired in a muffle furnace, although with care a nice job may be done with a blowpipe, a Bunsen burner, or even an alcohol lamp.

In case a Bunsen burner or lamp is used, it is well to have a metal tripod supporting a sheet of metal or wire mesh on which to set the work, as holding it by a pair of tongs becomes very tedious.

A muffle may be heated by electricity, gas , oil, coal, or wood. Electricity or gas, however, is preferable, as they are not accompanied by dirt. The muffle itself, which is simply a small oven, is generally made of fire clay, although both fused quartz and nickel are sometimes used. A door to the muffle is not necessary, although it is an aid to cleanliness. If, however, a door is used it should have a hole in it large enough to allow the enameler to watch his work constantly. It is very important to keep the enamel work away from the oxidizing effect of the fire; so that any cracks that appear in a muffle must be immediately repaired. It will be found very advantageous, too, to have the doors of the furnace on the side of it opposite to that containing the mouth of the muffle.

The pieces to be fired should be laid upon a tray of a size convenient to pass easily through the mouth of the muffle. These trays are made preferably of sheet nickel for this metal will not scale or flake off when heated and so contaminate the enamel. As these trays become quite hot it is advisable to handle them by means of a pair of long-handled tongs.

Before placing a tray of pieces in the muffle to be fired, it is well to leave it near the mouth of the muffle for a minute or two so that the enamel may become entirely dry before it is placed in the muffle, for if damp the enamel will be blown off of the metal by the rapid evaporation of the water which it contains.

When the pieces are fully dry, the tray may be placed in the muffle, which should be heated to a bright red heat of about 1400? F. With such a heat it should take from half a minute to two minutes to "fire" or melt the enamel. The time required will vary with different enamels and can only be learned by experiment. The enamel should be kept in the muffle until it begins to melt and its surface becomes fused and comparatively smooth and glossy, when it should be removed from the furnace and allowed to cool in the air. It is not necessary or even desirable to fire the enamel perfectly smooth in the first firing. It generally takes at least two coats, that is two chargings and two firings, before a piece is ready to be stoned. If, however, only one coat is to be used, it should be fired as smooth as possible.

When the pieces cool, the metal will be found covered with a black scale caused by oxidation. This may be removed by simply brushing it, which operation in most cases will clean the piece sufficiently for the second charging. Otherwise the piece may be "pickled," or cleaned with acid.

Subsequent firings do not differ from the first one except that in the last firing the enameler should try to obtain as smooth a surface as possible.

After the last firing the pieces should be submerged for a minute or two in a mild pickle consisting of one part sulphuric acid and one part water. This will clean off the oxide and make the metal bright.

If red enamel is used it is best to throw the piece into a cup of thick heavy machine oil to cool instead of letting it cool in the air. This will give the red a greater brilliancy. Red enamel, too, often requires a greater heat than other colors, although too low a heat tends to destroy the gloss on any enamel. Many delicate colors which are opaque when fired at a low heat, will become opalescent and in some cases transparent if fired at a higher temperature. Red enamel loses its color if fired too many times, and a large number of firings have a weakening effect on high-karat gold.

STONING

AFTER a piece of enamel has been fired, it is often found that too much enamel has been used, that is, that the enamel may have run over the edge of the part to be enameled, or it may not present a smooth surface but instead consist of a series of humps, or, especially in the case of transparent enamels, it may be on in such layers that the color is deepened or even lost entirely.

This can be remedied by what is known as "stoning," or filing the enamel down to a smooth surface. In the case of work that is to be polished it is always considered best to overcharge the piece and then file it smooth rather than to try to "flush" it evenly.

Stoning is usually done by means of emery "stones" or "sticks," which are made by mixing powdered emery with shellac and heating the same until the mixture coheres, when it may be pressed into any shape desired by means of a flat piece of steel. On cooling the stones become very hard. They are generally from six to twelve inches long and from three-eighths to one inch square, tapering at both ends to a rather blunt point. When a stone wears out or loses its shape it can be remelted and remodeled. The emery used in these sticks runs from No. 70 to No. 180 grit.

Carborundum stones are often used in place of emery stones. They are rather more expensive than emery stones and wear out quicker, but they cut the work down much faster. No. 120 and No. 180 grits are the most satisfactory. These stones sometimes get filled up with metal, but in this case the metal can be eaten out with acid.

It is convenient when stoning to hold the piece to be stoned on a small block of wood, on which a mold of shellac has been made into which mold the piece of work will snugly fit. If the block is then set on a pivot either on a bench or bench-pin, so that it will turn easily, it will then be found that the stoning process has been made considerably easier. A piece of hard felt or leather or just a plain piece of wood will, however, answer the purpose. The idea is simply to hold the piece firmly and conveniently.

The stone should now be rubbed back and forth across the enamel as a file is used. It is necessary when stoning to keep both the stone and the piece to be stoned quite wet. A bowl full of water kept near by will be found very convenient for the purpose. Care must be taken not to make any deep scratches on the metallic parts of the piece, as these scratches cannot easily be obliterated.

The stoning should be continued until the surface is smooth or level with the edges, or until in champlev? and cloisonn? enamel the metal parts all show evenly, or until the desired depths of color are obtained in the case of transparent enamels. This of course can only be judged by experience, as the colors will look much brighter when fired again.

When the stoning is finished it will be found that the surface of the enamel presents a rather dull or dead appearance, which will be removed by again firing the piece. Before this firing, however, the piece should be submerged for about a minute or less in hydrofluoric acid and then brushed in clean water. This may be done with any small stiff-bristled hand brush. The piece will dry readily in the air, but more quickly if first dipped in scalding hot water or brought in contact with steam. It may also be dried in hot air or sawdust. When dry it is ready to be fired.

Sometimes after stoning, low places or pit-holes are found in the enamel surface, which may be remedied by re-charging these places with enamel and then firing the piece.

When only a very small amount of enamel is to be stoned off, or when one does not want to fire the piece after the stoning, a soft soapstone called a "Scotch stone" may be used to advantage.

If the piece to be stoned is small it is desirable to have a small wooden stick the size of a pencil with which to hold the piece steady and keep it from slipping out of its mold. Of course a mold is not always necessary, but will often be found very convenient.

A sharp steel tool, such as a three-cornered scraper or a slightly dull awl, is very useful to clean out pit-holes or to chip enamel off from places where it is not desired.

When a large number of pieces are to be stoned, it is advantageous to use an emery or carborundum wheel of No. 90 to No. 120 grit, from two and one-half to six inches in diameter and from three-eighths to three-fourths of an inch thick, revolving on a lathe at a low rate of speed. A stream of water should be kept constantly dropping on the wheel in order to keep both the wheel and the work wet.

Rubber cots are a great protection to the fingers, which are gradually worn away by the stones.

POLISHING

AFTER an enameled piece has been stoned and fired for the last time, it is often desirable to give the enamel a gloss or polish additional to that which it naturally receives from the firing.

If the metal used is other than fine gold or fine silver it will be black or oxidized when taken from the furnace, in which case it should be "pickled," that is, submerged for a minute or two, until the oxidization is removed and the metal becomes bright, in a mild "pickle" consisting of a warm solution of one part sulphuric acid and one part water. The piece should now be rinsed in clean water, after which it will be ready to be polished.

Polishing is best done on a lathe with a swiftly revolving wheel, say about 2200 revolutions per minute. A wheel of from three to six inches in diameter, made of hard felt or wood, is very satisfactory. If the felt is thin it is often necessary to make a wooden back for it in order to keep it flat.

The piece to be polished should be held on a small piece of leather or felt so that the hands may not come in contact with the wheel, in which case the skin and nails would soon be worn away. Rubber finger cots will serve as an additional protection.

The enamel surface to be polished should first be covered with wet pumice of about the consistency of mud. Then the pumice-covered surface should be pressed against the face of the felt or wood wheel, and as soon as the pumice is removed by the action of the wheel more wet pumice-mud should be added so that the enamel surface may constantly be kept covered with wet pumice.

It is best to use the finest ground pumice obtainable, although on rough jobs a coarse grade may be used. Tutty powder is said to give even a better polish than fine pumice, and is often used after a preliminary polish has been given by pumice. A different wheel should be used for each polishing compound.

The polishing should be kept up until the enamel surface takes on the desired gloss. This polishing process will cut away the metal quicker than it does the enamel, so that any slight lines and scratches which the metal received in the stoning will be removed by the polishing. Care must be taken not to polish away too much of the metal, or to cut down and destroy any metal ornaments which may be near the enameled part of the piece. Felt wheels being more pliable than wood wheels have a tendency to cut down the metal faster than they cut down the enamel , while wood wheels tend to cut down both parts equally. Felt wheels, however, are considered to give a better and quicker polish.

When the piece is polished sufficiently, it should be rinsed and brushed off in clean water, which will remove all trace of the pumice. The piece is now finished as far as the enameling process is concerned, but may, however, be plated, set with stones, engraved, etc., as may be desired.

If after the piece is polished it is found that there are a number of small pit-holes in it, in which the pumice sticks even after the brushing, this may be remedied by digging the pumice out with a scraper or any sharp instrument. If the hole is small and the enamel transparent it will scarcely show when clean owing to the refractive power of the enamel. If, however, the hole is so large and noticeable as to be objectionable it will have to be re-charged and re-fired. In such a case it is often possible after the first firing to stone it smooth with a Scotch stone or by polishing and thus avoid another firing.

FOILS--PAILLONS--GLITTER ENAMEL--DULL FINISH--PLIQUE-?-JOUR

FOILS and paillons are generally made of fine gold or fine silver leaf. Silver foils are used on copper and gold work in order to obtain better enamel effects, for most transparent colors are shown to best advantage over silver. Gold foils are sometimes used on copper for similar reasons.

The metal is first charged and fired with a coat of any enamel, preferably a "hard running" white, that is, one that it takes a comparatively high temperature to melt. The foil is then stuck to the enamel by means of gum arabic, tragacanth or, in fact, some kinds of common mucilage will answer the purpose. As Cunynghame says, "What is wanted is a good tenacious gum, which disappears as completely as possible when heated and leaves no carbonaceous residue to spoil the enamel." The foil should be cut so that it will exactly fit the enamel surface, and cover it entirely so that none of the white enamel will show on the finished piece. If the foil is stamped with some design it will add greatly to the brilliancy of the enamel afterwards applied, and if it is pierced with a number of small holes through which the fumes of the gum can escape, it will stick smoothly to the enamel.

After the foil has been put upon the enamel, the piece should be fired until the foil adheres strongly and smoothly to the enamel, when it is ready for the next charging. From this point on the process does not differ from that employed when charging directly upon the metal.

Paillons are simply small bits of foil cut into dainty and artistic shapes such as stars, fleurs-de-lis, etc. They are applied by means of gum, as in the case of foils, on the surface of the last or upper layer of colored enamel, after it has been fired, and the piece is again fired, making the paillons adhere to the enamel. The piece is then charged all over with a coat of fondant and fired, after which it is ready to be stoned and polished, if desired.

Glitter enamel, called by the Germans "flimmer," is simply ground up goldstone mixed with an ordinary enamel in equal proportions or two parts of goldstone to one of enamel. Some very striking effects can be produced with this mixture, which should be stoned to bring out the brilliancy of the goldstone. The best effects are obtained when some dark opaque enamel is used.

To obtain the so-called dead or dull finish on enameled goods, it is only necessary to submerge the piece for two or three minutes in a solution of hydrofluoric acid. This will "etch" the enamel leaving the surface dull like ground glass. When the piece is etched evenly all over, it should be removed from the acid and washed and dried. The etching will only take a few minutes if the acid is strong, and will be done much more evenly if a mixture of hydrofluoric acid and ammonium carbonate, known as white acid, is used.

If only part of the surface is to be dulled or etched, the part that is not to be etched should be covered with shellac, or a mixture of three parts beeswax and one part Burgundy pitch, and allowed to dry before the piece is put in the acid. The acid must be kept either in lead or wax bottles, as it eats glass very rapidly. Its fumes are very dangerous and destroy human tissues.

If for some reason a piece has been enameled wrong, so that it is desirable to take the enamel off the metal, this can best be done by leaving the piece for a few hours in a solution of hydrofluoric acid which will eat the enamel, so that it can easily be brushed off the metal, leaving it bright.

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