Pitch is the process that a material for removing impurities undergoes resulting material gold, silver or platinum high purity.

Common methods of tuning:

pyrometallurgical processes

Pyrometallurgy is a branch of extractive metallurgy in which processes for obtaining and refining or refining of metals are employed using heat, as in the case of casting.
It allows obtaining metals from their ores, directly or after concentrated, by heat. The metal is mainly extracted -from is mineral-, by separation -of bargain- ore and purification of metals

hydrometallurgical processes

It involves removal, metal recovery using liquid solutions, aqueous and organic.
It is based on the concentration of solutions in one to several elements of interest metals, present as ions, that by reversible reactions and physical differences of the solutions are separated and isolated in a specific way. As a result, a solution rich in the ion of interest is obtained..