Matte is a term used in the field of pyrometallurgy given to the molten metal sulfide phases typically formed during smelting of copper, nickel, and other base metals.^[1] Typically, a matte is the phase in which the principal metal being extracted is recovered prior to a final reduction process (usually converting) to produce blister copper.^[1] The matte may also collect some valuable minor constituents such as noble metals, minor base metals, selenium or tellurium. Mattes may also be used to collect impurities from a metal phase, such as in the case of antimony smelting.^[2] Molten mattes are insoluble in both slag and metal phases. This insolubility, combined with differences in specific gravities between mattes, slags, and metals, allows for separation of the molten phases.