Colonial button or rosette ? Anyone see a design on it ?

[Gregg3131]

Found this at a colonial site ! Anyone see a design in black on the trim or just natural wear ? Not sure if this is a button ? Heavy and does not seem like a shank . Any ideas ?

 

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[DCMatt]

I think it's too small to be a rosette. Looks like the soldered shank fail. I don't see any pattern on the front or back, but it's still pretty crusty.

 

[Mud Hut]

Need a better photo of the "shank"