Scientific American 9, 27.2.1869
Zinc may be given a fine black color, according to Knaffl, by cleaning its surface with sand and sulphuric acid, and immersing for an instant in a solution composed of four parts of sulphate of nickel and ammonia in forty of water, acidulated with one part of sulphuric acid, washing, and drying it. The black coating adheres firmly, and takes a bronze color under the burnisher. Brass may be stained black with a liquid containing two parts arsenious acid, four hydrochloric acid, and one of sulphuric acid in eighty parts of water.
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