I've used a lot of acetone on silver, probably enough to kill plenty of brain cells over the years. My acetone comes in metal cans, what appears to be ordinary "tin cans" which, according to a bit of reading, likely contains no tin, or, at the most, a tin-plating. Otherwise our "tin cans" are aluminum, iron or steel. Three articles say acetone is "safe for metal." Recently I've picked up some Norwegian coins, and, before tucking them away in holders I'd like some advice from those of you who know from experience or research: would you recommend an acetone bath for: - Bronze? - Iron? (WW I and WW II issues) - Zinc? (WW II issues) Thanks, folks! Steve
There's ongoing argument over whether acetone can discolor copper, which is fairly non-reactive. The general consensus seems to be that if you get water in the acetone (maybe just from a humid environment), and there's light involved, the acetone can break down to form acetic acid, which will attack metals. I suspect there's other contamination involved in most cases. Zinc is a very reactive metal. If impure acetone can do anything to copper, it can certainly do things to zinc. Bronze is copper alloyed with other (even more reactive) metals, and iron is pretty reactive itself. My inclination would be to do a quick acetone rinse on iron coins, to dry them thoroughly and prevent rust. For soaking any of these three metals, it might be better to use xylene; it'll dissolve oils and resins, probably better than acetone, and it can't contain the acids that can damage metals.
I've experienced discoloration with two bronze coins — a British India 1/4 anna and a 1 cent coin from Sierra Leone. By the same token, I've soaked probably hundreds of other bronze coins in acetone with no ill effect whatsoever. I've used acetone on several zinc WW2 European issues with zero problems. No experience with iron coins.
I would suggest finding a few junk bin iron or zinc coins and do a test run on coins you don't care about to make sure you are happy with the results. In general, if your metal has corrosion, a cleaning is not going to fix that. The corrosion itself damages and roughens some of the underlying coin texture, so even if you could chemically reverse the reaction (which is possible), the surface is never going to be like new again. If in doubt, better to leave things alone.
In my experience using acetone, the only metal I've had issues with is aluminum. I don't think I've ever done iron, however.
No issues with zinc or iron, though I treat both if those metals very differently than other coins after an acetone soak. For aluminum, xylene seems to have better results than acetone.
I have a great many Norwegian coins, many of them bronze. I get them sent from my wife's family in Norway. These two bronzes, for some reason were sellotaped to a piece of card. 3 days in acetone, with regular rinsing with distilled water and then fresh acetone and there is no residue to be seen. No color change or visible damage to the surfaces
