This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Yellow to bright red: Dissolve 2 parts native copper carbonate with 1 part caustic soda in 10 parts water. Dip for a few minutes into the liquor, the various shades desired being obtained according to the length of time of the immersion. Green: Dissolve 1 part copper acetate (verdigris), 1 part blue vitriol, and 1 part alum in 10 parts of water and boil the articles therein. Black: For optical articles, photographic apparatus, plates, rings, screws, etc., dissolve 45 parts of malachite (native copper carbonate) in 1,000 parts of sal ammoniac. For use clean and remove the grease from the article by pickling and dip it into the bath until the coating is strong enough. The bath operates better and quicker if heated. Should the oxidation be a failure it should be removed by dipping into the brass pickle.
A verdigris color on brass is produced by treating the articles with dilute acids, acetic acid, or sulphuric acid, and drying.
Brown in all varieties of shades is obtained by immersing the metal in solutions of nitrates or ferric chloride after it has been corroded with dilute nitric acid, cleaned with sand and water, and dried. The strength of the solutions governs the deepness of the resulting color.
Violet is caused by immersing the thoroughly cleaned objects in a solution of ammonium chloride.
Chocolate color results if red ferric oxide is strewn on and burned off, followed by polishing with a small quantity of galena.
Olive green is produced by blackening the surface with a solution of iron in hydrochloric acid, polishing with galena, and coating hot with a lacquer composed of 1 part varnish, 4 parts cincuma, and 1 part gamboge.
A steel-blue coloring is obtained by means of a dilute boiling solution of chloride of arsenic, and a blue one by a treatment with strong hyposulphite of soda. Another formula for bluing brass is: Dissolve 10 parts of antimony chloride in 200 parts of water, and add 30 parts of pure hydrochloric acid. Dip the article until it is well blued, then wash and dry in sawdust.
Black is much used for optical brass articles and is produced by coating with a solution of platinum or auric chloride mixed with nitrate of tin.