I regularly see much older coins, which have been slabbed and certified as Mint State, having dark spots/areas around raised areas and the rims. I presume these certified coins have not been cleaned. How can most of the surface of these coins be clean and only the raised areas and rims be dark/discolored?
In the case of the first coin it has spent years in either a paper wrapped roll or in a cardboard holder. The paper/cardboard contained sulfur compounds which caused the coin to tone/tarnish and the area around the rim/edge of the coin that was in closest contact with the paper/cardboard has toned darker than the rest of the coin.