RoadRunnerJD posted about a 69 Barracuda 340S fastback:

"Distributor Hold Down Clamp: Copper Plated"

I have a 69 340S also with a copper plated hold down clamp. But the copper plate on my clamp originally had a black coating on top, maybe paint - not sure. I scrubbed it with a mild abrasive, and the black came off.

Can anybody discuss details about this metal finish? Is it actually black paint over copper plate, or some chemical reaction on top of the copper?

I've seen plenty of discussions about finishes like zinc plating with chromates and dichromates, and phosphating, but I've never seen a finish discussed anywhere that had copper plate on steel with something black on top.