The malleability of copper and its efficiency as a conductor of electricity are greatly reduced by even the slightest impurities in the metal. The electrolytic process of refining is used because it gives a higher grade of refined metal from a greater range of impure copper than is the case with the poling process.

Electrolytic refining consists of dissolving plates of blister copper by electrolysis and depositing the metal from solution upon a previously prepared sheet of pure copper. The current gradually dissolves the plate of blister copper and deposits the metal almost absolutely pure upon the other plate. The impurities from the dissolved sheet either go into solution in the liquid of the tank in which the process is carried on, or fall to the bottom in the slime.

A plate of copper thus prepared is too porous for use, hence it is melted and cast into cakes, ingots or wire-bars, as may be needed.