9. A very weak solution of bichloride of platinum, applied with a hair pencil or by immersion. Used for binding screws, holders, and other small articles of copper and brass.
10. Sulphate of iron and sulphate of copper, of each 1 oz.; water, 1 pint; dissolve; wash the surface of the articles with it; let them dry; then apply a solution of verdigris, 2 oz. dissolved in strong vinegar, 1⁄4 pint; when dry, polish them with a soft brush, and either some plumbago or colcothar. Used for tin castings.
11. The articles (properly cleaned) are either immersed in, or washed over, with a solution of sulphate of copper or of verdigris. In a short time they acquire a coating of pure metallic copper, and are then washed. This only answers with iron and steel goods. It is admirably suited for iron castings.
12. An antique appearance may be given to
silver by either exposing it to the fumes of hydrosulphate of ammonia, or immersing it for a very short time in a solution of hydrosulphate of ammonia, or in dilute nitric acid.
Bronzing, Sur′face. A term commonly applied to the process of imparting a bronze-like or metallic appearance to the prominent portions of the surfaces of figures made of paper, wood, plaster of Paris, &c. It is effected by first giving them a coat of oil-varnish or size, and when this is nearly dried, applying, with a ‘dabber’ of cotton, or a camel-hair pencil, any of the ordinary metallic bronze-powders before referred to. Sometimes the powder is placed in a little bag of muslin, and dusted over the surface. The articles should be afterwards varnished.
Paper is bronzed by mixing the bronze-powders up with a little weak gum-water, and burnishing the surface when dry and hard.
Electrotypes, to Bronze. Green. Steep the medal or figure in a strong solution of common salt, or sugar, or sal-ammoniac, for a few days; wash in water, and allow to dry slowly; or suspend it over a vessel containing a small quantity of bleaching powder, and cover over. The length of time it is allowed to remain will determine the depth of colour.
Brown. Add four or five drops of nitric acid to a wine-glassful of water. The object is rubbed over with this gently, and allowed to dry, and when dry subjected to a gradual and equal heat; the surface will be darkened in proportion to the heat applied.
Black. Wash the surface over with a little dilute solution of hydrosulphate of ammonia, and dry at a gentle heat.