Beautiful and durable rainbow colorations are imparted to zinc by a very simple process. The zinc to be thus treated may be in any form, cast or sheet, the special requisites being that it be pure, dry, polished or filed; the coloration is the more brilliant according as the materials of the bath are pure, and thus the best effects are obtained with chemically pure reagents. The bath consists of 30 grammes tartrate of copper, 40 grammes caustic potash and 400 grammes distilled water. On subjecting the zinc to the action of this kind of bath for a couple of minutes it appears an agreeable violet; for three minutes, a deep blue; four and one-half minutes, green; six and one-half minutes, a golden yellow; eight and one-half minutes, purple violet.
(2) To save zinc a black color dip the article in a boiling solution of 3 17-100 ounces sal-ammoniac and 5 64-100 ounces pure green vitriol in 4 1/2 quarts of water. The loose black precipitation on the articles is removed by means of a brush and the article is again dipped in the hot solution and then held over a coal fire until the evaporation of ammonia salt. A repetition of this three or four times gives a black coating of tenacious adherence. By the surpension of zinc in a nickel bath, slightly acidulated with sulphuric acid, a blue-black coating is formed without the employment of a current. The same result can be secured by dipping the zinc articles in a solution of 2 11-10 ounces of a double sulphate of ammonium and nickel, and a like amount of sal-ammoniac in 1 quart of water. The article assumes first a dark yellow color, and then becomes brown, purple-violet and indigo-blue in succession, and will stand a slight brushing with a scratch brush and polishing.
(3) The various colors on zinc are obtained as follows: To give it a reddish-brown color, rub with a solution of chloride of copper in liquid ammonia. To give it a yellow-brown shade rub with a solution of chloride of copper in vinegar. To give it a copper-red color immerse the article in a bath of chloride of copper and dissolve in spirits of sal-ammoniac. To give it a yellowish tone add crystallized verdigris. To give it a bronze color rub it with a paste of pipeclay, to which has been added a solution of 1 part tartar, 2 parts crystallized soda and 2 parts crystallized verdigris.