Discolored Gold

Ask an Expert From: Products Finishing, , from Powder Coating Consultants, Div. of Ninan, Inc.

Posted on: 7/1/2005

Question: What causes gold plate to discolor?

Question:

What causes gold plate to discolor? I. V.

Answer:

There are a number of possible causes for a gold plate to discolor. I can give you some general information but since you did not specify the type of plating bath or the base materials, I cannot give you specific recommendations.

For a classic gold cyanide type plating bath some possible causes of discoloration are:

 

Symptom Probable Cause
Deposit has a reddish or brown hue. Gold content is low.
Cyanide content is low.
Temperature is low.
Current density is not correct.
Deposit is reddish in color. Copper present in plating bath.
Deposit is greenish in color. Silver or cadmium present in plating bath.
Deposit is blackish in color. Lead or arsenic present in plating bath.

 

Another possible cause of discoloration is that the deposit is too thin and porous. For example, if gold is plated over silver and the gold layer is porous some of the silver can migrate through the pores to the surface and form silver sulfide.

Another cause of discoloration can be if gold has been plated directly over a base material that can migrate through the gold layer. Gold applied directly over copper is one such example. To prevent this from happening a barrier layer is plated on the base layer and gold is then plated over the barrier layer.



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