Obs. The above are used by painters, japanners, &c. See Bisulphide of Tin (Tin), Powders, &c.
BRONZ′ING. The process of giving a bronze-like, or an antique metal appearance, to the surface of copper, brass, and other metals. The following methods are recommended for this purpose:—
1. To the surface of the article, first thoroughly cleaned and polished, evenly apply with a brush the common crocus powder (‘jewellers’ rouge’), previously made into a smooth paste with water. When dry, place it in an iron ladle, or on a common fire-shovel, and expose it over a clear fire for about one minute; lastly, when sufficiently cold, polish it with a plate-brush. This gives a very rich appearance, similar to that on tea-urns; the shade depending on the duration and the degree of heat employed.
2. As the last, but substituting finely powdered plumbago for crocus powder. Equally beautiful, but deeper coloured and more permanent than that produced by No. 1.
3. As the preceding, but employing mixtures of plumbago and crocus in various proportions according to the shade desired.
4. A dilute solution of liver of sulphur (sulphurated potash), or of hydrosulphate of ammonia is applied with a camel-hair pencil to the metal previously slightly warmed; when dry, the surface is either left rough or brushed off. If liver of sulphur has been used, it will be better to wash it first in clean hot water; but without the slightest friction. This gives the appearance of very antique bronze.
5. Verdigris, 2 oz.; and sal-ammoniac, 1 oz.; are dissolved in vinegar, 1 pint; and the mixture is diluted with water until it tastes only slightly metallic, when it is boiled for a few minutes, and filtered for use. Copper medals, &c. (thoroughly clean) are steeped in the liquor at the boiling-point until the desired effect is produced. Care must be taken not to keep them in it too long. When taken out they are carefully washed in hot water, and dried. Effect as the last.
6. Verdigris and vermilion, of each 2 oz.; alum and sal-ammonia, of each 5 oz. (all in fine powder); vinegar, q. s. to form a thin paste. This is spread over the surface of the copper, which is then uniformly warmed by the fire, and afterwards well washed and dried. The tint may be deepened by repeating the process. The addition of a little blue vitriol inclines the colour to a chestnut-brown; and a little borax to a yellowish-brown. Used by the Chinese for copper tea-urns, &c.
7. Sal-ammonia, 1 oz.; cream of tartar, 3 oz.; common salt, 3 oz.; hot water, 1 pint; dissolve; then add of nitrate of copper, 2 oz., dissolved in 1⁄2 a pint of water; mix well, and with it repeatedly moisten the article (placed in a damp situation) by means of a soft brush. Produces a very antique appearance.
8. Salt of sorrel, 1 oz.; sal-ammoniac, 3 oz.; distilled vinegar, 1 quart; dissolve. As the last. Much used for bronze figures.