They say that copper coins require a different cleaning process than bronze, and that what works for one could ruin the other. How does one tell the difference? They all look the same to me...
Distilled water should be your first step to cleaning...safe for all coins. Then if you need extra help, try acetone. Should be safe on any metal. Depending on the dirt, also try olive oil as a third step If none of the other two above work, and it should also be safe for copper and bronze. If none of the above do the trick and you need extra strength stuff, I think a mixture of half amonia half distilled water should be safe on just about anything, though it may give copper a little bit of an unnatural pinkish color. Just don't use any amonia on potin or anything else containing nickel.
The short answer.... you can't. Roman coins in particular used a variety of metals and the only way to know it's composition would be to do a metallurgical analysis, which unfortunately would destroy some of the coin. RIC I can't remember which volume, gave the composition of some coins and they were a hodgepodge. Also don't forget our friend orichalcum. You can tell these coins by their golden outer layer, and corrosion reveals a reddish/orangish center.
Thanks! I got one of those "uncleaned lots" and am hoping for the best. They've been soaking in distilled for the past 3 days, and are starting to look actually pretty good.
Bronze is bronze colored - copper is copper colored. Its a fairly dumb answer but holds up in almost all circumstances.
