By any chance, did you try to use muriatic acid? The reason I ask, is that I notice the copper ground wires in electrical boxes have massive amounts of patina within a couple weeks of the masonry guys power washing the brick on houses.
I did not try muriatic acid. If I recall there were 2 reasons my nephew suggested the acetic acid. One was to etch the copper. The other reason was that it is also a chemical used in a reaction to create copper acetate - 1 type of "green copper". He thought with a little luck it would etch the copper a well as assist in turning it green. I did notice a slight, barely noticable green haze on the copper but nothing like the end result.
I'm sure the muriatic acid would etch the copper but I'm not sure how much. I would test it out on a piece of scrap just to make sure it doesn't eat away too much.
