Coins mostly need a quick wipe with just toilet paper soaked with acetone or a cloth , a cloth is better but you also have to wash it because acetone is a smelly solvent that you really don't want to be handleing , ever . This removes all the gunk from coins , you know the stuff that gets transfered from years of being handled in peoples pockets , removes all the grease and dirt and give the underneath a chance to shine through again Soap and water also works as well but just not as fast , several washes might be needed . Remember NEVER rub to hard or the coin might end up with surface scratches