Hello Everyone, Not sure what this is, at first It looked to be a RPM, but now that I look closer, it seems to be some type of lamination problem. I guess it could be some type of bubble under the mm, sure would appreciate some opinions. This coin is a 1986d Lincoln Cent.
You got it right, it is a trapped gas bubble under the copper layer,, if the top were removed you would more than likely find a corroded area of the zinc core.
it is very common on these copper plated zinc cents .
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