Foils. These are leaves of polished metal, put under stones or pastes, to heighten the effect. Foils were formerly made of copper, tinned copper, tin, and silvered copper, but the latter is used for superior work at the present day. There are two descriptions of foils employed, viz.: white, for diamonds and mock diamonds, and colored, for the colored gems. The latter are prepared by varnishing the former. By their judicious use the color of a stone may be often modified. Thus, by placing a yellow foil under a green stone that turns too much on the blue, or a red one turning too much on the crimson, the hues will be brightened. By the skillful use of the following varnishes, good imitations of the gems may be cheaply made from transparent white glass or paste, and when applied to foils set under colored pastes, (factitious gems), a superior effect may be produced. The colors must be reduced to the finest state possible by patient grinding, as without this precaution, transparent and beautiful shades cannot bo formed. The palest and cleanest mastich, and lac dissolved in alcohol, and also the palest and quickest drying oil, should alone be employed, when these substances are ordered. In every case the colors must be laid on the foils with a broad soft brush, and the operation should be performed, if possible, at once, as no part should be crossed, or twice gone over while wet.               

2448. White or Common Foil

2448.    White or Common Foil. This is made by coating a plate of copper with a layer of silver, and then rolling it into sheets in the flatting mill. The foil is then highly polished or varnished.

2449. Colored Foils

2449.    Colored Foils. These are made by coloring the preceding foil, highly polished, with certain transparent solutions or varnishes. The following produce beautiful colored effects, when judiciously employed.

2450. Blue Foil

2450.    Blue Foil. Prussian blue, ground with pale, quick-drying oil. Used to deepen the color of sapphires. It may be diluted with oil.

2451. Green Foil

2451.     Green Foil. Pale shellac, dissolved in alcohol (lacquer), and tinged green by dissolving verdigris or acetate of copper in it. Or: Sesquiferrocyanuret of iron and bichromate of potassa, of each 1/2 ounce; grind them with a stone and muller to a fine powder, add gum mastich (clean and also in fine powder), 2 ounces; grind again, add a little py-roxilic spirit, and again grind until the mass becomes homogeneous and of a fine transparent green; the beauty increases with the length of the grinding. The predominance of the bichromate turns it on the yellowish green; that of the salt of iron, on the bluish green. For use it is to be thinned with pyroxilic spirit. This is used for emeralds. It may be brightened by adding a little yellow varnish.

2452. Yellow Foil

2452.      Yellow Foil. Various shades of yellow may be produced by tinging a weak alcoholic solution of shellac or mastich, by digesting turmeric, annotto, saffron, or soeo-trine aloes therein. The former is the brightest and most fit for topazes. Or : Digest hay saffron in 5 or 6 times its weight of boiling water, until the latter becomes sufficiently colored; filter, and add a little solution of gum or isinglass. "When dry, a coating of spirit varnish should be applied.

2453. Bed Foil

2453.    Bed Foil. Carmine dissolved in spirits of hartshorn, or a weak solution of salt of tartar, and gum added as above.

2454. Garnet Foil

2454.      Garnet Foil. Dragon's blood dissolved in rectified spirit of wine. (See No. 2449 (Colored Foils).)

2455. Vinegar Garnet Foil

2455.     Vinegar Garnet Foil. White foil (see No. 2449 (Colored Foils)) varnished with orange lake finely tempered with shellac varnish.

2456. Amethyst Foil

2456.      Amethyst Foil. Lake and Prussian blue, ground fine in pale drying oil.

2457. Eagle Marine Foil

2457.    Eagle Marine Foil. Verdigris tempered in shellac varnish (alcoholic), with a little Prussian blue. "With this varnish white foil. (See No. 2449 (Colored Foils).)

2458. Ruby Foil

2458.    Ruby Foil. Lake or carmine, ground in isinglass. Or: Lake ground in shellac varnish. Used when the color turns on the purple. Or: Bright lake ground in oil; used when the color turns on the scarlet or orange. Either of these are applied to" white foil. (See No. 2449 (Colored Foils).)

2459. To Make an Imitation Diamond more Brilliant

2459.    To Make an Imitation Diamond more Brilliant. Cover the inside of the socket in which the stone or paste is to be set with tin foil, by means of a little stiff gum or size; when dry, polish the surface,. heat the socket, fill it with warm quicksilver, let it rest for 2 or 3 minutes, after which pour it out and gently fit in the stone; lastly, well close the work round the stone, to prevent the alloy being shaken out. Or: Coat the bottom of the stone with a film of real silver, by precipitating it from a solution of the nitrate in spirits of ammonia, by means of the oils of cassia and cloves. (See Silvering Glass.) Both these methods vastly increase the brilliancy both of real and factitious gems.