BRONZING. The process of imparting a bronze-like or antique metallic appearance to the surface of metal, as copper and brass, ivory, plaster or clay, and wood. The bronze effect ou metals is frequently produced by beating bronze to thin leaves, similar to those of gold, which are then made into a paste with a size and applied to the metal. Sometimes bronze powders, such as mosaic gold or aurum musirum, which con sists of equal parts of sulphur and white tin oxide melted together until they assume the appearance of a yellow, flaky powder, are em ployed. The many bronze powders of various names, as, for instance, Dutch gold, are similar to the foregoing, and consist of various ingredi ents, and are applied with size to the metal. Articles to which these various mixtures have been applied should be coated with a clear varnish, or otherwise the object will soon lose its metallic appearance. There are also a great number of bronzing liquids in which a metallic object may be dipped. They have a wide range of color as well as of composition, and formulas that are applicable to brass, copper, and zinc are to be found in the various technical receipt books. Among the well-known bronzing-liquids for gun-barrels is a mixture of 1 part nitric acid, 1 part sweet spirits of nitre, 2 parts alcohol, 4 parts copper sulphate, 2 parts tincture of iron chloride, and GO parts water. The green Patina effect of ancient bronze is frequently imitated by coating new articles with a liquid consisting of 1 part ammonium chloride, 3 parts cream of tar tar, 3 parts common salt dissolved in 12 parts of boiling water, to which is added S parts of a solution of copper nitrate. An antique appear
ance is often produced on silver by exposing it to the fumes of ammonium sulphide, or immersing it in a similar solution. Ivory may be gilded by immersing it in a solution of ferrous sulphate and then in a solution of gold chloride; and to coat it with silver the ivory is dipped in a weak solu tion of silver nitrate, after which it is immersed in clear water and exposed to the rays of the sun. The ivory then acquires a black color, which, on being rubbed, is changed to brilliant silver. In the bronzing of plaster or clay the figure is usually coated with an isinglass size until it will absorb no more. It is then slightly coated with gold size, and after drying, the figure is painted with bronze powder, and when com pletely dry the surplus powder may be rubbed off. A bronze effect is produced on wood in a somewhat similar manner. The wood is first coated with a mixture of size and lampblack, and then a suitable bronze powder, as of Dutch metal or mosaic gold, is laid on with a brush, and when thoroughly dry rubbed with a soft woolen cloth.