Unfortunately that is surface staining (or more precisely it looks like the natural toning of copper has been stripped away). That makes this damage as well. I do not think it is due to incomplete mixing of the alloy.
"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
Agree with Spence. For fun, try giving the coin a long soak in 100% acetone. May (may...) remove or reduce any dried surface crud/film which might be involved.
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