As part of the etching process, you use asphaltum (known in printmaking as hard ground) to block the areas not to be eaten away by the acid bath. After the acid etch is complete, one must remove the asphaltum. The best way to do it? Use a giant blowtorch! As a cool effect, the asphaltum reacts to the extreme heat (1500 degrees F) by turning a comical shade of St. Paddy’s Day green.
In the picture, you see the copper sheet stacked on blocks, surrounded by lava rocks with a 3″ wide, 12″ long cone flame.