What can I do to save this guy? It was given to me as a gift but the back of the coin has some black gunk on it. No idea what it is other than it's very unatractive. Thanks Darryl
If it's PVC residue, from being stored in a soft vinyl flip, a bath in pure acetone might help. If it's tarnish (silver oxydation), a light dip in thiourea might remove it. I wouldn't suggest the thiourea for anyone who has never used it.