Georgivs ii rex 1760 gold? [solved]

This coin was in a glass pendant to be worn around the neck it has left grey material around the edge wondered the best way to remove it if possible and any information about the coin would be welcome.

The coin is a copper half penny coin which has been plated. I suspect you probably want to leave it as is instead of returning the edge to the original copper.
https://en.numista.com/catalogue/pieces19984.html

Thanks bjherbison for the information.