Smelter's dross is a term used to describe the waste material that is produced during the smelting process. SCORIA is a type of volcanic rock that is often used as a by-product of smelting and is one of the components of smelter's dross. It is composed of small fragments of lava with gas bubbles frozen into the rock. Smelter's dross is usually composed of a variety of materials, including slag, ash, and other impurities.