Which of these is a thin layer that forms on the surface of copper through age and exposure?

Thank you Antiques Roadshow! Got this right because I heard it before on their show when evaluating coins.

Electric motors with a commutator will also get a patina on them

I always thought. it was verdigris specifically on copper

Seshati , I heard it on an episode of Sherlock

Thank you Barnwood Builders

Thank you Jimmy Smits character from Sons of Anarchy haha I mean I’ve seen it sure but didn’t know the name until he said it in the show .. looked it up & will never forget it. It’s pretty can really make a piece into art of a different kind.