This is assuming you're talking about collectible coins that have some numismatic value. On modern clad, just tumble them or clean them anyway you can so that they will go through the Coinstar or you're able to spend them without being given the 3rd degree. Unless it's a rare date/mintmark, late silver and wheats don't have much, if any, collector value in "dug" condition. You can tumble those as well without hurting the value. First you have to determine potential value by carefully finding out the date and mintmark by using soap, warm water, and a soft bristled toothbrush to start. If you need more than that, soak it in some olive oil for a few days and use a Q-tip and/or toothpick remove the crud. Then look up the coin to see if there is any value attached to it. Check for varieties that may have been made that year too. At the same time, try to figure out what the grade would be if it was completely clean. There are places online where you can get that info or get the ANA grading standards book so you can figure it out. If it's a rare coin, you may want to stop right there and get some professional advice on whether you should continue cleaning or leave it alone. If it's common and only worth the metal value or type, clean it to look the way you want.
