Carl- I have a theory about a way to remove the spots without damaging the coin. It's a process that can work on stamps without even damaging the gum of mint stamps. The problem is, I would never test a highly graded coin and most "lowballs" are too worn to have any spots left! I want to test copper, nickel, and silver coins but need to figure out where to find inexpensive spotted and/or toned coins to work with.