As much as I dislike digging pennies at the beach, I've come to appreciate that finding them can help offset the cost of the batteries. However, a good number that I dig up are in pretty encrusted. I cashed about 1500 in today at the bank and a number were rejected by the machine. I'm wondering if anybody has any good ways to get the crustacion off? I know a rock tumbler would probably work, but they don't hold that many coins and also run up the electricity bill. Just wondering if there is some kind of solution they can be soaked in?