The term “impurities” has different meanings; however, in gold mining and refining, impurities refer to something that lowers the karat weight or millesimal fineness of a sample of gold. Impurities may be used to alternate gold’s physical properties like hardness or appearance. Just like blending different kinds of paint to create new shades, blending gold with other metals creates new colours. Impurities jumbled together or alloyed with the gold like iron or nickel become as waste products of the refinery process.