Is the affected area raised above the rest of the design or merely demarcated by an encircling fissure? If the latter, it would most likely be a struck in piece of scrap.
@dear, I think that something either was stuck or still is stuck to the surface of this coin. The area around this was exposed to the environment or a chemical of some sort more than the metal underneath so there is differential toning.
"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
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