A crude form of copper extracted from oxide ores or roasted sulfide ores in a blast furnace. It typically contains between 70 and 90 percent copper, with the remainder being iron, sulfur, and other impurities that give it a dark, blistered appearance. It requires further refining in a converter or reverberatory furnace to become commercially useful.
Heard on the job
The tap from the blast furnace gave us a heavy yield of black copper, but the iron content is still too high for the wire mill.