Very cool stuff. I came across this quarter that looks like it has a blister. Its definitely not a die chip or PMD. I have never seen this before so I believe it to be a very rare mint error. Has anyone else ever seen this before? What causes it?
Its been exposed to heat, probably a torch or soldering iron. since copper has a lower melting point than nickel, it melted within the clad layer, and the weakened nickel “gave way” and warped. At least thats the most likely way for me to see that happenening. Either way, It is PMD.