Bronzing. An imitation of bronze may be produced on the surface of other alloys and metals either by corrosive chemical solutions, which is the most efficient way, or by coating them with varnish and bronze powder. In most large towns bronzing-liquor for brass and zinc can be purchased where chemicals are sold. Bronzing is very largely applied to brass-works of various kinds, and especially to gas-fittings. For this purpose the following solutions are used, but the brass is first pickled with nitric acid and scoured with sand and water, or it may be treated with a potash solution.
For dark olive-green bronze, muriatic acid and arsenic; sometimes iron scales are added. Afterwards brush with black lead and coat with yellow lacquer. For steel-gray bronze, boiling solution of chloride of arsenic. For brown bronze, solution of the nitrate or perchloride of iron. For black bronze, solution of the chloride of platinum. To produce on new bronze an imitation of the patina on an antique bronze, a mixture in hot water of sal-ammoniac, cream of tartar, common salt, and nitrate of copper is used. Salt of sorrel, sal-ammoniac, and vinegar is another mixture employed.
Iron castings are very effectively bronzed by covering them with an electro deposit of copper in the form of a thin film or layer, which can then be darkened by any of the chemical bronzing solutions, and either lacquered or varnished. The copper surface is often simply varnished. Many beautiful foreign statuettes in zinc are also bronzed in this way. See ELECTRO-METALLURGY.
A brown colour, sometimes called a bronzing, is given to the surface of iron and steel objects by a concentrated solution of trichloride of antimony (liquid butter of antimony), having a specific gravity of 1.35. This has been a good deal used for gun barrels.
Coating with Gold or Bronze Powders.—Metal, wood, plaster of Paris, and other materials can be coated with these in the form of a paint. Doors, friezes, cornices, and other parts of rooms are now frequently bronzed in this way. When bronze powder is used, the wood or plaster first receives three or four coats of yellow oil paint, then two coats of a mixture of the bronze powder with flat varnish, and finally this is covered with another layer of varnish. If it is desired to give an object with bas-reliefs or other raised ornaments the appearance of a bronze, changed more or less to green by time and exposure, perhaps the most tasteful way is to partially gild the projecting portions and paint the rest of the surface of a sombre green, running the colour partly over the gold.