Fire!
I have a couple like this and in addition to the curvature they clearly shows signs of fire damage.
Both are large antoninani like this too.
SC
The effect of heat is an interesting idea, but I can hardly imagine without mechanical effect of thermal expansion so it does not
work in physics, except that if the heat only reaches the middle, but the metals are
good thermal conductors and immediately equalize the temperature ...
In any case, it is interesting.
I think it could have been some mechanical effect that was even intentional.
Regards
Joe