In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with:

Copper is extracted via self-reduction (auto-reduction). During the process in the Bessemer converter, a part of the cuprous sulphide is oxidized to cuprous oxide. These then react with each other to produce metallic copper:
$$2{\text{Cu}}_2\text{O}+{\text{Cu}}_2\text{S}\to 6\text{Cu}+{\text{SO}}_2\uparrow$$
The copper obtained is called "blister copper" due to the escape of ${\text{SO}}_2$.