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Gold Plating looks good but blackens with age

Our Center conductors are gold plated for electrical resistance purposes. When parts return from the plating process, they are clean and look free of plating salts or contaminants. However, a few months later, there is a black growth on these parts. Sometime, the black penetrates the gold finish and renders the part useless. This usually happens to assembled product where any type of heavy agitation in a cleaning process may damage the assembly. I would like to know what causes this black growth and how I can prevent it from happening

Tony Tubaro
Electronics - Hartland, Michigan
2004

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2004

Because of the cost of gold there is enormous and continuous pressure to keep reducing the specified thickness. If you look at gold plating specs from 40 years ago you would find that gold plating thickness was typically 10x what it is today. The chemistry has improved greatly but today's thicknesses are often marginal at best because pragmatism dictates that we just keep pushing the envelope.

Maybe a nitric acid porosity test could demonstrate that the gold is too thin, maybe not. Yes, there are other possible explanations for the black growth, but try doubling the gold thickness on some sample parts before investing months of study on esoterica :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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What is under the gold? Silver and copper will migrate right through the gold and show tarnish on top. Give us more information

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004