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Anti tarnish for copper coating on imitation jewellery

Q. I do imitation Rose gold ( which is an alloy of Cu-Ag). I WANT A GOOD Anti tarnish, not E-coat which has to withstand 1% polysulphide test, so that glitter/sheen of the jewellery stone should not diminish.

Panjala Mukesh Goud
Employee - Hyderabad, India
September 4, 2025

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A. Hi Panjala

Is there an ASTM, ISO. or other standard governing this 1% polysulphide test you are speaking of? I understand what polysulphide is, and that it can blacken and otherwise corrode copper, but I'm not understanding how you conduct this test or interpret the results.

The best copper preservatives to forestall tarnishing of copper are sodium benzotriazole and related compounds, and they are quite routinely applied to copper surfaces, but I don't know whether they will get you past the requirements of a test that I'm not familiar with.

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted can be retained for immediate
answers or long term project help

The test is supposed to be for silver plating on top of copper wire. After the procedure, the surface turns black from reaction with the copper base metal when the silver plating is not fully protecting the copper. Since you are plating a copper-silver alloy instead of unalloyed silver, the ASTM B298 test may not work no matter what you do. Perhaps I am wrong and the alloy plate layer does not discolor in the test procedure. If that is the case, your best bet is to plate a thicker coating.

Jon Barrows, MSF, EHSSC
Kansas City

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