plating, anodizing, & finishing Q&As since 1989
Layers on top of the core of 92.5% silver jewelry
June 1, 2010
I have a question from a supplier who is currently sourcing from China, his questions are:
If the product only conforms to 92.5% silver (the core not the layers) should it be marked as 95% ( most Chinese factories do this!)
The client said they usually use 2 layers on top of the core silver to stop tarnishing which accounts for the 5%. These materials are rhodium and Palladium and other foreign materials.
What bonding agents do they use to seal these layers together on top of the silver? and what other foreign materials do they use in this 5%?
The client has told me that when the products are on display under lighting with heat, they develop a strange spot tarnish effect on the product and he wants to know the reason for this ?
Also he said his products are usually in storage for 2+ years before being sold, during the time in storage tarnishing occurs, I didn't ask him about what type of environment the products are stored in, any ideas?
Inspector - Hong Kong
June , 2010
Hi, Jason. Did I misunderstand you, or are you asking if it is okay for you to fraudulently label the jewelry as 95% because most other jewelry from China is fraudulently labeled? The justification for such fraud is that rhodium and palladium are precious metal worth more than silver, so if it is plated, that somehow "equals" more silver? :-)
Silver tarnishes. Rhodium plating (it is applied by electroplating, not with bonding agents) is good at deterring tarnish but is too thin and porous to last forever. If the jewelry is stored for years, it probably must be stored with volatile corrosion inhibitors (VCI), or some sort of jewelry cloth to deter tarnish.
The silver and rhodium eventually diffuse together, the hotter it is, the faster the diffusion; so if the jewelry is under very hot incandescent lamps, I suppose that would speed the diffusion and cause faster tarnishing. Good luck.
Ted Mooney, P.E.
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