My daughter started collecting coins recently and she brings me anything wired. We have a half dollar with a blister on the face. Looks like something tried to puncture it but the back is normal. My next thought was heat. Maybe it was in a fire and started to melt? It does have some discoloration on it. Any thoughts on this one?
I found a Kennedy with similar damage a couple of months ago. I was told it was post mint damage, I don't know what people do to these poor coins! Let me see if I can find the images...
I agree with your deduction. Most likely your coin was in a fire. A small air bubble between the clad layers built up pressure with the increasing temperature of the coin. When the outer clad layer became hot enough to become plastic the bubble expanded and pushed that outer clad layer out. When the coin cooled the bulge in the outer clad layer remained.
