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topic 18178

Chemically polishing copper to a mirror finish


I want to chemically polish a copper (or copper alloy) machined part to a high finish with removal of minimal material. I've tried various acids, but with negligible success. Can anyone suggest a chemical, not mechanical, method that will produce a mirror finish?

Thank you.

George Jerome
- Chatsworth, California, USA


George, please try to post what acids you tried and how you applied them, and in what ways they produced unsatisfactory results. The way you've posted the question, readers will be reluctant to try to answer it only to, in all probability, be publicly redressed that "we already tried that, it doesn't work" :-)

But if you haven't, look into nitric acid bright dipping of copper and phosphoric acid electropolishing of copper. But I believe that there is no chemical treatment that will produce a mirror polish starting from a rough finish. Good luck!

Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Try a solution of 0.5% v/v sulfuric acid along with about 25% v/v hydrogen peroxide at about 110 degrees F. Keep the part in for about 3-4 minutes. There should be a brown smut on the part. Rinse, and then remove the smut using a 5% v/v solution of sulfuric acid. This should be pretty good, but I would still try to buff it for the best finish.

Dan Brewer
chemical process supplier - Gurnee, Illinois


Hello, I repaired a copper tube chair recently, one of the tube was damaged so I replace it by an other that I shaped to fit like the original. My problem is now that it does not have the mirror finish I wanted. I used some polishing paste I had, but the final result was kind of hazy. Can someone recommend a procedure and some product I should use. Thanks in advance, nice day to all.

Sylvain J.Durocher
fabricator - Casselman, Ontario, Canada


George, I have found that if you want to chemically remove layers of copper, you can use Ferric Chloride, (FeCl3) this is a chemical found in PC Board etchant solution. After you have removed the copper that you want, you need to polish lightly to get to that mirror shine. I did this on a 1924 95% Copper penny to bring it back to shiny, I polished it by rubbing between my thumb and fingers, it was a mirror shine in about 30 minutes, the only problem that I found is that it is a brighter color than that typical brown/red/gold type tint than new coins. I did recently find out that it is because the planchets they use to mint pennies are oxidized slightly by air before and after minting on their way to circulation. So I will just have to wait and watch it obtain that toning through a few weeks of oxidation. Hope this helps, Cheers!

Josh Clowers
- Holton, Indiana USA

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