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Brown Patches on Gold Plating

I have a zinc diecast piece that's plated with Ni and flash gold. After 2 weeks of storage(covered with acid-free film)small tea coloured patches are found on the surface. The patches are irregular in shape and can be wiped off easily. What is the possible cause?

WY Wong
- HK
2001

2001

Sometimes it's hard to fit all the datapoints, so you have to just throw one away. It sounds to me like either cyanide bleedout from the copper strike (assuming there was one, or that the gold flash is so thin that the nickel is tarnishing. In either case, I can't particularly explain why the stain wipes away so easily so I'll throw that data point out :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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