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  for Metal Finishing since 1989
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Silver plating solution turns yellow

2004

We use silver cyanide (minimum 99% AgCN) for silver plate and silver strike solution. When we first mixed the silver strike solution by using silver cyanide 3.13 g/l with potassium cyanide 95 g/l, It looked clear in yellow color and well dissolved, But two weeks later the solution change to dark yellow color, and after 45 days has some brown suspended solid. In these two weeks and 45 days, we have not done anything with the solution at all. The suspended solid seems to pile up everyday. Please give us some advice about this incident. Our silver plate parts have sometimes blisters .

Could you please advise to reduce this problems.

Best regards,

Malee N.
Plating shop - Bangkok , Donmuang, Thailand

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2004

This is normal. As silver is plated out of the complex Potassium Silver Cyanide and with electrolysis and high temperature the cyanide molecule breaks down into an organic polymer which is dark yellow to brown. This may be carbon treated out, but with each carbon treatment you also soak out some of the silver metal. The presence of this organic polymer narrows the efficient and bright current density range.

Also some commercial brighteners contain carbon disulfide which break down into organic polymers that are dark. These also narrow the best platable current density range.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

About this issue , maybe you can add the process of passivation, that becoming a thin film on the silver, and prevent it be oxidized, but this process will affect the production's electrical performance. and another method is that the part is packed by vacuum and adding the desiccant

Leaf ye
- Shanghai, China
2004