blister copper

Blister copper is a form of metallic copper with a black, blistered surface, typically 98.5% to 99.5% pure. It is produced during the converting process in copper metallurgy, where molten copper matte is treated to remove iron and sulfur.12

The extraction of copper generally involves three steps: mineral processing to concentrate copper minerals, smelting or leaching to remove impurities like iron and sulfur, and refining to achieve high purity. In the converting stage, air is blown through molten matte, oxidizing remaining iron and sulfur. This process yields blister copper, which then undergoes fire refining to further reduce sulfur and oxygen levels before being cast into anodes for electrolytic refining.23