We generally ascribe that bubbling to extreme heat and call these "campfire coins". Whatever the cause, it is damage rather than a mint error.
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz