Chemically polishing copper to a mirror finish

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" :-)

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.

A. George, I have found that if you want to chemically remove layers of copper, you can use ferric chloride ⇦ this on eBay or Amazon [affil links] , (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!