Nickel sulfate is the most widely used salt for nickel-plating baths, and is known in the plating industry as single nickel salt. It is easily produced by the reaction of sulfuric acid on nickel, and comes in pea-green water-soluble crystalline pellets of the composition NiSO4.7H2O, of a specific gravity of 1.98, melting at about 100°C. Double nickel salt is nickel ammonium sulfate, NiSO4.(NH4)2.SO4.6H2O, used especially for plating on zinc. To produce a harder and whiter finish in nickel plating, cobaltous sulfamate, a water-soluble powder of the composition Co(NH2SO3)2.3H2O, is used with the nickel sulfate. Nickel plate has a normal hardness of Brinell 90 to 140, but by controlled processes file-hard plates can be obtained from sulfate baths. In electroless plating, nickel sul-fate, a reducing agent, a pH adjuster, and com-plexing and stabilizing agents are combined to deposit metallic nickel on an immersed object.
The electroless nickel coating is comparable to electrolytic chrome.