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. (See chapter on charging.)

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 (Aventurin) 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.

Plique-À-jour enamel may be done in several ways. The simplest is to lay the filigree work upon a piece of mica or fire clay and charge with enamel, as if the mica or fire clay were the background and the filigree work the sides of the piece. The process continues the same as in ordinary enameling, except that just before the last firing the mica or fire clay should be removed.

Copper or silver foil may be used instead of mica, but in this case the filigree work must be either of gold or platinum, for the copper or silver foil can only be removed by being dissolved in nitric acid.

The most difficult way is to mix a little gum arabic or gum tragacanth with very finely ground enamel and charge a layer on the inner sides of the wires which make up the filigree work. The gums will hold the enamel in place after it is dried. When the piece has been fired, another layer of enamel should be charged and so on, until by degrees the entire space between the wires has been filled up. This process is tedious and requires much skill and care, but gives very satisfactory results.