Temperature and the amount of Oxygen that can be bonded by the copper can alter the color. Use a mini-butane torch and you can make a Black pearl on Red ( if you are careful and practice) There are two oxides of copper. Copper(I) oxide (cuprous oxide, Cu2O) , red color forms below 300 C Copper(II) oxide (cupric oxide, CuO), brown,black oxide that forms above 300 C Continued heating to 1326 C results in melting and at 2000C, it boils. Black and red copper oxides Jim
Okay, then, if it was "struck on a red-black planchet", how'd they get the red highlights on the date, letters, and rim?
No it is not. Those Cook Island coins are reflecting a black object placed in front of them Your Cent is a dirty coin. Please stop.
That is a proof set. Just get the lights and the camera in the correct position and you’ll get the same black background with shiny frosted raised letters, numbers and objects. As for the cents, I’d like to see the label.
Look at his picture.. The Cent in question is not even placed correctly within the prongs Most likely In one of these DIY slabs..