Painting on zinc or galvanized iron is facilitated by employing a mordant of 1 quart of chloride of copper, 1 of nitrate of copper, and 1 of sal-ammoniac, dissolved in 64 parts of water. To thin mixture add 1 part of commercial hydrochloric acid. This is brushed over the zinc, and dries a dull-grey colour in from twelve to twenty-four hours, paint adhering perfectly to the surface thus formed.
The following are the formulae for a variety of baths, designed to impart to polished brass various colours. The brass objects are put into boiling solutions composed of different salts, and the intensity of the shade obtained is dependent upon duration of the immersion. With a solution composed of sulphate of copper, 120 grains; hydrochlorate of ammonia, 30 grains; and water 1 quart, greenish shades are obtained. With the following solution, all the shades of brown, from orange-brown to cinnamon, are obtained: chlorate of potash, 150 grains; sulphate of copper, 150 grains; and water, 1 quart. The following solution gives the brass first a rosy tint, and then colours it violet and blue: sulphate of copper, 435 grains; hyposulphite of soda, 300 grains; cream of tartar, 150 grains; and water, 1 pint. Upon adding to this solution ammoniacal sulphate of iron, 300 grains, and hyposulphite of soda, 300 grains, there are obtained, according to the duration of the immersion, yellowish, orange, rosy, and then bluish shades. Upon polarizing the ebullition, the blue tint gives way to yellow, and finally to a pretty grey. Silver, under the same circumstances, becomes very beautifully coloured. After a long ebullition in the following solution, we obtain a yellow-brown shade, and then a remarkable fire-red: chlorate of potash, 75 grains; carbonate of nickel, 30 grains; salt of nickel, 75 grains; and water, 10 oz. The following solution gives a beautiful dark-brown colour: chlorate of potash, 75 grains; salt of nickel, 150 grains; and water, 10 oz. The following gives in the first place, a red, which passes to blue, then to pale lilac, and finally to white: orpiment, 75 grains; crystallized sal-sodae, 150 grains; and water, 10 oz. The following gives a yellow-brown: salt of nickel, 75 grains; sulphate of copper, 75 grains; chlorate of potash, 75 grains; and water, 10 oz. On mixing the following solutions, sulphur separates, and the brass becomes covered with iridescent crystallizations: (1) cream of tartar, 75 grains; sulphate of copper, 75 grains; and water, 10 oz. (2) Hyposulphite of soda, 225 grains; and water, 5 oz. Upon leaving the brass objects immersed in the following mixture, contained in corked vessels, they at length acquire a very beautiful blue colour: hepar of sulphur, 75 grains; ammonia, 75 grains; and water, 4 oz.