I know you aren't supposed to clean coins and I never do, but I just found a nickel roll searching last night and it has a nice error on it. It also has a huge greasy thumb print on it that you can see when you magnify it. I was wondering if there is a safe way to clean that off without cleaning the coin or damaging it. Will Kleenax just rub it around, will acetone hurt the coin or the value of it? Thanks in advance