It's common on silver coins it's pvc residue. It's easily removed with acetone if one were inclined to. I don't alter my coins in any way. That's how I received it that's how I'm sending.
hi- nice auction-the pvc residue is NOT common in silver coins.it can occur in any type of coin if it is NOT housed in a an acid free holder.acetone in general can remove the residue , if the coin is dipped lightly.the acetone makes the luster on a coin appear flat.it is not advised to clean any coins .