Strange toning on this 1837 dime (not my image or coin)

[James_OldeTowne]

What caused that weird circle on the obverse?

 

NGC AU-53:

 

James

[TJ'S Coins]

Looks like it might be an outline of a finger or perhaps something laid across the coin as it was stored.

[EZ_E]

I also think that it was perhaps a finger pressing it into an album even though no fingerprints are showing.

[MikeInFL]

I cannot fathom a guess as to what toned that coin that way, but I do not believe it was a finger -- it is way too small...Mike

[Hoot]

The coin has the toning pattern of many mercury dimes I've pulled from blue Whitman coin folders (where a person can't see the backside of the coin). Typically, the coins go in white, often from a poor dip, then obtain a black toning on the reverse and rims over time. The odd green is disturbing and I find the coin rather ugly overall.

 

Hoot

[TomB]

I don't think the obverse marking is from a fingerprint, it looks more like something adhered to the surface and was improperly removed.