Discolored Gold Plate

Why does gold plating stain after a month of use?

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Q. We plate a thin layer of gold over silver parts. To prevent migration of the silver into the gold plate, we plate the silver with a nickel strike before gold plating. We are finding that the gold plate tends to stain after a month or so of use. What is causing this problem?—B.F.

A. There are a number of possible causes for the discoloration. I would start by looking at the gold plating bath. Is it clean and free of tramp metals? If your chemistry is OK (cyanide concentration, gold concentration and so forth) look for tramp metals such as copper, silver, and cadmium. The next step is to look at your nickel strike bath. Tramp metal contamination of the strike bath might also cause this problem. Lastly, investigate the thickness of the nickel strike. If it is not heavy enough, it may be porous and will allow the silver to bleed through and cause the gold to stain.

Originally published in the July 2015 issue.

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