BRONZING is the process of covering plaster or clay figures, and articles in ivory, metal, and wood, so as to communicate to them the appearance of ordinary bronze. Several of the materials employed are of little value, whilst others are expensive. Thus, gold powder is used for the finer work, and is prepared by grinding gold-leaf with honey on a stone slab till a very fine state of division is attained, then washing out the honey, and drying the gold powder. Inferior gold-leaf, or that which con tains much silver and copper, yields the German gold powder employed in bronzing. Copper powder is prepared by introducing an iron bar or plate into a solution of copper, when tho latter metal is precipitated as a finely-divided red powder. _Mosaic gold, or musivurn, is made by fusing 1 lb. of tin, introducing lb. allowing the alloy or amalgam to cool, then pulverizing and grinding up with alb. sal-ammoniac, and 7 ozs. sub limed sulphur. Ultimately, the whole is subjected to the process of sublimation, when the tin, as a brilliant yellow powder, resembling gold, is left in the subliming vessel. The color of mosaic gold may be deepened by the addition of red oxide of lead, and it then assumes a copper tint. Gold size is prepared by heating 1 lb, of linseed oil, and gradually adding, 4 ozs. of gum animi in very fine powder. When boiled sufficiently, it assumes the consistence of tar, and may then be strained through cloth. When employed in bronzing, some vermilion is added, to make it opaque, and turpentine, to make-it thin and limpid enough to be easily laid on the plaster cast or other article with a brush, and the object may ultimately be rubbed over with soft chamois leather, which is occasionally dipped into the gold size. The other 13. powders are best laid on with a solution of gum-arabic or isinglass, either of which acts as a cement.
Gun-barrels are bronzed by acting upon them with the chloride or butter of antimony (bronzing salt), or with hydrochloric or nitric aeids, when the surface of the iron gets partially eaten into, and covered with a thin film of oxide; after which the gun barrel is thoroughly cleaned, oiled, and burnished. A brownish shade is thus commu nicated to the barrel, which protects it from rust, and at the same time renders it less conspicuous to an enemy or to game. In the bronzing operation known as the Damas cus, the barrel is treated with dilute nitric acid and vinegar, to which sulphate of copper has been added. The result iq, that metallic copper is deposited irregularly over the iron surface; and when the latter is washed, oiled, and well rubbed with a hard brush, a very pretty appearance is communicated to the barrel. Articles in wood that require to be bronzed, are first coated with a mixture of size and lampblack, and dried, and then a bronze powder, consisting of very finely-divided patent yellow, raw umber, pipe clay, lampblack, and Prussian blue, is put on with a brush. After being dried again, the article is burnished with cloth or leather, covered with a layer of Castile soap, and, lastly, cleaned Up with a woolen cloth. Copper vessels, coins, etc., are bronzed by beating them in a copper boiler containing vinegar, with 2 parts of verdigris, 1 of sal ammoniac dissolved in it, when, after sufficient boiling, a pleasant reddish-brown hue is imparted. BrOnze and copper articles may have an antique appearance commu nicated by applying a solution of sal-ammoniac 1 part, cream of tartar 3, common salt 6, hot water 12, and more or less nitrate of copper, when an ancient greenish hue is obtained.