Question

Why it is called Blister copper??

Answer 1

metallic copper of a black blistered surface, being the product of converting coppermatte and being about 98.5 to 99.5 per cent pure. — called also Bessemercopper.

Answer 2

The slightly impure copper had impurities, mostly sulphur dioxide which bubbled up through the copper as it solidified. That gave a blistered surface and the results of the smelting were called blister copper. It had to be worked to release all the gas