I have been trying several thing's as of late, I was able to use some of the swimming pool Chlorine test kit chemical's on a few no date buffalo nickel's and managed to get some minor results. I haven't tried it on silver yet. There is a product you can buy at some grocery store's for cleaning the lime and scale out of electric coffee maker's that will clean Clad and Nickel coin's like new without the scrubbing that will damage the coin, Just be sure to rinse it well with soap and water, Then follow that with a rinse of Isopropyl Alcohol or Acetone based nail polish remover. As for my thot's on silver, I wonder if you could place a magnet with a sheet of paper over it and place the coin on top of it, and lay another paper over the coin and sprinkle some iron powder or Filing's and see it the magnetic field passing thru the coin would give you an outline of the date and other feature's?
I do know that the coin's once struck will have a different density where the date, legend, and portrait are. That is how some law enforcement agencie's are able to find serial number's. I do recall seeing a forensic's show on the tube, that they used superglue and some type of acid to form a residue on a object to show what the eye and the microscope couldn't...... Alway's try the least harmful way to clean a coin and make sure you protect yourself from exposure to any type of chemical's.......Rule No.1 USE YOUR BRAIN.......... No.2.... If you don't understand something, Google it.......