It looks like a piece of pressed copper that has a warm patina on the front. I'm guessing that it was made for another purpose and that the pin backing was added later.
The detailing in the scrollwork is very fine.
It has no markings as far as I can see for the maker or age, so your guess is as good as mine!
Measures 2.5 inches long by 1.25 inches high: an easily wearable size. Lightweight and delicate but sturdy.