I wasn't sure what that black mark was, and it prob wont come off. Acetone is good on gum and stuff like that. Paint, etc. I thought it might be old magic marker, but IDK what it is.
what is “op”. ?? Yeah I have a lot of coppers. Fortunately our banks still have them!!! Bought 5$ in pennies and have gain a couple of vg Wheaties and about 2/3 copper. That almost every week!! About to go to nickels and dimes!! I love copper!! I’m an electrician!!