Steffanie, I don’t know if this is still the approved way, but eons
ago I was taught to grasp the piece of copper with a pair or tongs
or pliers,and while holding it over a bucket of water to burn the
asphaltum off with a torch. This is a smelly process, and I don’t
know how safe it is to be inhaling the fumes. Perhaps there is a
I now use PNP as a resist for etching, and use ferric acid as my
mordent. You might want to check this process out.