Possible Rosetta

[streakert]

It seems lite, gold gilt over copper,
I can't decide if it's horse tack or a large button.
Found at an mid 1800s cellar hole

 

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[HuntinDog]

Looks like it has a lost attachment point in the middle, but also at 11 and 5 o'clock.
so could be either, but with the roughness of the back I'm thinking Rosette.

 

[DCMatt]

Possibly from a curtain tie back.