Gilding by Immersion.—For this purpose a solution is used which slowly attacks the metal to be gilded, and at the same time deposits on its surface an equivalent of gold. Elkington's patent solution is made by dissolving oz. troy of fine gold in 21 oz. of nitro-muriatic acid, heating this until red and yellow vapors cease to be evolved, then diluting with 1+ pint of distilled water, adding to this 1 lb. of bicarbonate of potass, and boiling for two hours. The article to be gilded is dipped into this at nearly the boiling het and agitated in it for about.a minute. Talbot's patent solution is made by adding a solution of gold to a solution of gallic acid in water, alcohol or ether. The articles are dipped as above.
The method called Grecian gilding is a process intermediate between the above and water gilding. Sal ammoniac and corrosive sublimate are dissolved in nitric acid, and gold is dissolved in this solution, which thus becomes a mixture of chloride •f gold, and nitrate of mercury ivith seine ammonia. This solutiOn. bitttig :applied to a swim: of silver, immediately blackens it, but upon the application of heat, it is richly' gilded.
Most articles that are gilded by either of the above chemical methods, or by electro-gilding, are submitted to an after-process of coloring. This consists either in acting upon the surface With a saline solution, and heating the article afterwards, or in coating it with a kind of varnish of bees'-wax and yellow-ocher, and then burning it off. Various saline solutions are used, many of which are carefully guarded trade secrets. 1 oz. alum, 1 oz. of common salt, and 2 oz. niter, dissolved in half a pint of water, is recommended. Also 24 parts of niter, 10 alum, 5 sulphate of iron, 5 sulphate of zinc boiled together in sufficient water to form a paste when cooled, with continual agitation. The articles are immersed in this, and then heated till the desired color is
obtained.
Cold gilding.—For this a gilding powder is first prepared by dissolving 5 dr. of pure gold and 1 dr. of copper in 10 oz. of nitro-muriatic then moistening clean linen rags with the solution, and burning them to ashes. These ashes contain finely divided gold, which may be applied to surfaces of copper, brass, or silver, by simply rubbing it over them with a piece of cork moistened with a solution of common salt in water.
Sword-blades, lancets, and other steel articles are gilded in fancy devices by drawing the design with a camel's-hair pencil moistened in a solution of gold, prepared by agi tating ether with a solution of terchloride of gold, and decanting the light liquid which floats on the top. Steel or iron can be gilded in a more durable manner by heating it and then applying gold leaf.
Silks, artificial flowers, ivory, bone, etc., may easily be gilded by immersing them in, or painting them with, a neutral solution of 1 part of terchloride of gold to 4 or 5 of water, then exposing them in a vessel containing hydrogen gas, which readily combines with the chlorine, and reduces the gold to the metallic state.
Encaustic gilding is usually applied to glass and porcelain. The gold is first obtained in a finely divided state by precipitating from the chloride with protosulphate of iron, or by simply the chloride.. This powder is ground up with of its weight of oxide of bismuth and some borax and gum water, and then painted on the ware. It is then heated till the borax is vitrified and the gold thereby fixed. Sometimes the gold is ground with turpentine, or an amalgam of gold is used. It has a brown dingy appear ance when it leaves the kiln; thd gold luster is brought up by burnishing.