Cluster of red bronze or copper acorns, vintage brooch w/pin back

We love this vintage costume jewelry pin, a cluster of dangling acorns with very worn gold colored (gilt?) finish over red bronze, copper or a non-magnetic metal of a deep coppery color. This isn't marked at all that we could see.

The entire piece measures 2 1/2" long end to end. There's quite a bit of tarnish, which we have not touched at all... we think this is beautiful just as it is.

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Item No. b10596