 An inclusion is a metal contamination of dross, if solid, or slag, if liquid.These usually are impurities in the pour metal (generally oxides, less frequently nitrides, carbides, or sulfides), material that is eroded from furnace or ladle linings, or contaminates from the mould.In the specific case of aluminium alloys, it is important to control the concentration of inclusions by measuring them in the liquid aluminium and taking actions to keep them to the required level.