Hi, I have a 1983 Olympic Silver Dollar Proof Set, and the half dollar appears to have a cladding flaw, or could this be something else? There are no signs that the sealed set have been tampered, so I'm a bit surprised by this as surely some sort of QA would have picked it up, if it is what I think it is! Any insight greatly appreciated - thanks!
It looks like it was exposed to some environmental contaminant. Those cases aren't really that air tight.
Very likely a water spot. There appears to be a few smaller ones near Kennedys nose. You should see what happens to a proof coin a few years after you sneezed on it. Welcome to CT.
Like I said in Post #5, those cases aren't that air tight. Even the airtites that the Mint uses aren't all that protective. Below is a Bicentennial silver proof medal that I acquired many years ago in a bulk purchase. It was terribly encrusted with an ugly haze. I submitted it to NCS with the hope that conservation would restore it to its original condition. As you can see from the before and after photos, the conservation wasn't 100% successful. Before After
