I recently found an Indian Head (late 1800's) in AU or possibly uncirculated condition... but it has been 'coated'. it appears to be something like a thick coat of varnish. Certainly it will preserve the coins current condition, but does it destroy the value of the coin, or is this considered 'acceptible'?
That's something from the old days. Many collectors used to coat their cents with lacquer in an effort to maintain the color and help protect the coins. It was said that you could safely remove the lacquer at a later date with lacquer thinner. Personally - I always felt it was a waaaaay bad idea. You can try removing the coating with acetone, but be prepared. In a period of time that can vary from days to a year or more the coin may turn more colors than the rainbow.
Of course that can happen with copper coins that have NOT been coated or treated with acetone as well.
I have seen autographed baseballs that were coated in the 30's era, but never coins. Does anyone have a pic?
