Looks like verdigris to me - looks like it has already started eating into the coin. Then again I am not an expert on verdigris versus PVC.
PVC is a catylist for verdigris formation created by hydrochloric acid forming cupric chloride. PVC damage and verdigris are essentially one in the same. On this coin, you're seeing verdigris which could have been caused by PVC or the environment. The first step is to soak it for about a hour in acetone. At the end of the soak and while the coin is still under fluid, I would prod at the spot with a toothpick to see if it comes apart. Acetone will NOT remove verdigris, but if there's PVC holding it together it will (mostly) come off.
Thanks Badthad. I have always thought of Verdigris as starting to eat at the coin and PVC as a slimy green substance that would turn into veridigris if let untreated. As it is it looks like if that comes off he will look like he had a vaccination shot.
I was really hoping there was someway to cure this coin, as I believe it to be a broken back variety from that year.
