Chemically polishing copper to a mirror finish
Q. 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
A. Hi George, if you haven't yet, look into nitric acid bright dipping of copper, or phosphoric acid electropolishing of copper. But I believe there's no chemical treatment that will produce a mirror polish starting from a rough finish. So it probably requires a good machining job. Good luck!
Please try to post what acids you tried and how you applied them, and in what ways they proved unsatisfactory. Readers might be reluctant to answer if they're likely to be redressed with "that's one we tried that didn't work" :-)
Ted Mooney, P.E.
Pine Beach, New Jersey
A. 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
Q. 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
A. 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
Small scale copper polishingJuly 23, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. My situation:I make pieces of art/furniture out of copper with soldered joints. I have to hand polish them after all of the soldering which is very time consuming and I'm looking for a faster way to restore the shiny finish.
Even if I can restore the copper colour and then give them a quick hand polish it would be a great improvement. I do need the shiny finish to last as long as possible.
Artist - West Midlands, UK
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