Not a real lot can usually be done with that situation. Sort of like those lines found on coins that were in a Whitman Folder a long time. That coin has had toning started where there was nothing to hinder it. Under the tape or whatever, the metal was protected. In such instances Acetone will not do much.
IF the coin is not excessively valuable, I'd say try dabbing a small amount of gun bluing solution to the clear spot. Not much to loose.
IF the coin is not excessively valuable, I'd say try dabbing a small amount of gun bluing solution to the clear spot. Not much to loose.





















