what happened to this quarter? the bumps aren't dents

probably the same thing that happened to this quarter.

Heated with a propane torch until some small gas pockets between the Cu-Ni clad and the Cu core expanded and created blisters on the surface.  Can you depress them (like I did on the side on the right)?

rsirian1

probably the same thing that happened to this quarter.

 

   

 

Heated with a propane torch until some small gas pockets between the Cu-Ni clad and the Cu core expanded and created blisters on the surface.  Can you depress them (like I did on the side on the right)?

yep

I wonder how bad the manufacturing of that material is.

would every quarter have volatile inclusions and blow up like pop corn if placed on a frying pan?

Mr. Midnight

I wonder how bad the manufacturing of that material is.

would every quarter have volatile inclusions and blow up like pop corn if placed on a frying pan?

 

I doubt a frying pan would get it hot enough but I will be trying it to find out.  Two things have to occur: there has to be enough gas (not necessarily volatiles, it can be just trapped air) and the temperature of the coin has to be high enough for the Cu-Ni to be soft enough to be deformed by the expanding gas.  For the coin I posted it had been heated to bright red hot (~900°C) about 300°C below the melting point of the Cu-Ni.