I would leave them alone. Sometimes what you do with a coin can ruin the value a lot. If they look altered and they are submitted to a grading company and lay view it as cleaned/altered, then they would note that on the slab. So it is best to leave them alone especially for a valuable coin. The dark spots will not come off. If you use too strong of a cleaner/dip they turn pink. Then the value is really affected. Best to leave them the way they are.






















