Two distinct processes have had this name applied to them. The first consists in staining brass work a dark brown or bronze color and lacquering it; the second consists in partially corroding the brass so as to give it that greenish hue which is peculiar to ancient brass work. The first is generally applied to instruments and apparatus, the second to articles of ornament.
1. The cheapest and simplest is undoubtedly a light coat of plumbago or black lead. After brushing the article with plumbago place it on a clear fire till it is made too hot to be touched. Apply a plate brush as soon as it ceases to be hot enough to burn the brush. A few strokes of the brush will produce a dark brown polish approaching black, but entirely distinct from the well known appearance of black lead. Lacquer with any desired tint.
2. Plate powder or rouge mar be used instead of plumbago, and gives very beautiful effects.
3. Make the articles clean, bright and free from oil or grease, then dip in aqua fortis, which must be thoroughly rinsed off with clean warm water. Then make the following mixture: Hydrochloric acid, 6 lbs.; sulphate of iron, 1/2 lb.; white arsenic, 1/2 lb. Be careful to get all the ingredients pure. Let the articles lie in the mixture till black, take out and dry in hot sawdust, polish with black lead, and lacquer with green lacquer.
Dissolve 1 oz. sal-ammoniac, 3 oz. cream tartar, and 6 oz. common salt in 1 pint of hot water; add 2 oz. nitrate of copper dissolved in 1/2 pint of water; mix well, and, by means of a brush, apply it repeatedly to the article, which should be placed in a damp situation.
Dissolve 10 parts of fuchsine and 5 parts of aniline-purple in 100 parts of 95 per cent, alcohol on a water bath; after solution has laken place, add 5 parts of benzoic acid, and keep the whole boiling for 5 or 10 minutes, until the green color of the mixture has given place to a fine light bronze-brown. This liquid may be applied to all metals, as well as many other substances, yields a very brilliant coating, and dries quick1::. It is applied with a brush.
1. Dissolve gum lac in four parts by volume of pure alcohol, and then add bronze or any other metal powder in the proportion of one part to three parts of the solution. The surface to be covered must be very smooth. In the case of wood, one or several coats of Mendon or Spanish white are given, and the object is carefully polished. The mixture is painted on, and when a sufficient number of coats have been given, the object is well rubbed. A special advantage of this process is that the coating obtained is not dull, but can be burnished.
2. Another method is to coat the object with copal or other varnish, and when this has dried so far as to become "tacky " dust bronze powder over it. After a few hours the bronzed surface should be burnished with a burnisher of steel or agate.