Electroplating of alloys sometime difficult to plate because its composed from different other metals. By using two or more metals can, with some difficulty, be electroplated simultaneously to give a mixed metal coating. The properties and appearance of such a mixture are, however, often different from that of the metallurgical alloy, which, having been melted, has come into metallurgical equilibrium.
Brass is electroplated from a mixed copper and zinc cyanide solution, and gold alloys from mixed cyanide solution of gold with copper, silver, zinc or nickel. The objective is usually to obtain a tin plating of a particular color for purely decorative purposes.
Bronze (copper-tin), speculum alloy (copper-tin) and tin-zinc alloys can be electroplated to achieve some of the advantages of each constituent, chiefly good corrosion protection with maintenance of appearance; control is difficult however. A true inter-metallic compound of tin and nickel can be electroplated. This has unique properties although rather dark, it is relatively untarnishable and gives good metal protection.
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