Once most of the impurities have been removed from the copper by smelting and converting, natural gas is blown into the blister copper to burn off the oxygen.

The natural gas is blown into the bath of blister copper through a small hole and the process takes two to three hours.

Once the oxygen has been removed, the copper is cast into molds to form a slab approximately one metre square called an anode.

		Casting copper anodes.
	Source

The copper anodes are then sent on to the final stage in processing: anode refining.