Matte conversion is the process by which the copper is separated from the left-over sulfur, iron and other metals not eliminated in smelting. It is a strong exothermal process, so secondary materials, such as recycled copper, can be added during conversion without the need for extra fuel to create more heat. Like in flash smelting, the practice is to enrich the air used in the process with oxygen.

Conversion yields a product called blister copper, which has a copper content of approximately 99%.