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topic 12337

Cleaning sterling silver before lacquering


My company does mostly jewelry finishing, precious metal plating of gold and silver. We have been using an electrophoretic lacquer over our plated silver with great success. I have recently received solid silver jewelry for coating and I can't figure out how to get this clean enough before coating. We are ultrasonic cleaning then going through a hot electrocleaner (without current) rinse, acid, rinse, di rinse, pre-dip before the electrophoretic lacquer. The parts are turning yellow during the curing process which is 305 degrees for 20 minutes. I have had to strip the lacquer and the yellowed lacquer comes off in sheets. I am not sure if the lacquer is yellowing in the baking process or if the lacquer is lifting a tarnish coat off the surface of the jewelry. The second time through the process the parts look great. Obviously I can't afford to clean like this! Can anyone help me?

Barbara Magnan
Spectrum Metal Finishing - Isle, MN, USA


This looks like an old post, but I have an opinion as to why you are experiencing yellowing in your curing process for your lacquer. My theory is that the lacquer is releasing oxygen during the curing process. This could be solved obviously by having a lacquer that does not release oxygen during the curing process or "pre-conditioning" your lacquer so that no oxygen is in it (or released during heating). Another idea I had is to pre-coat the silver with a thin layer of lacquer that does not need curing, then do the heat curing thing. Anyway, good luck. I probably need to get a life.

Clay W. Long
- Prospect, Kentucky

Ed. note: Thanks, Clay. Although the original post is indeed old, this site is largely about building a resource to help future readers. Just as it kind of doesn't matter whether you read the "Dear Abby" column from today's newspaper or last year's, your response is likely to help a future reader.

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