Concerning potatos, I was readinig Huckelberry Finn by Mark Twain and a character in that book recomended cleaning a coin in a potato. I guess the potato method has been used for a long time.
the potato method is like also using finger nail polish remover. the potato has the same substance as finger nail polish remover but not as nearly as concentrated (acetone). it is a natural chemical. i am not saying it is ok to eat finger nail polish remover (lol)...but both the potato and nail remover have the same substance that will clean your coins naturally!!!