First off the really valuable coins, cleaning is a NO GO. Don't do it because you can destroy their value. On copper coins, peroxide heated in a glass pan on the stove till boiling (barely). Set your coins on tooth picks so they don't lay flat on the bottom of the pan. Soak em like two minutes, take them out and rub with a Q-tip dipped in the peroxide and repeat. Don't get the heat too high or your coins will come out looking dull and dry. Works on nickels too, haven't tried silver as I am more respectful to them. I think I did once and the coin came out "blued". After you get your copper clean, many guys put wax on them to protect them and make them shine. I DON'T suggest soaking in olive oil because the copper absorbs the oil and for a long time afterward it leaks out of the coin. I have a couple hundred Indians I made that mistake with, however, I was able to use the heated peroxide to take some of the oil out of them. As with all cleaning methods, start with your worthless coins first and work your way to the better ones, that way you don't destroy a valuable find. If you search for posts from Don in south Jersey under cleaning coins< he posted some really good info on the Find Mall Explorer form. Good luck to you.