Dross

Dross is a mass of solid impurities floating on a molten metal or dispersed in the metal, such as in wrought iron. It forms on the surface of low-melting-point metals such as tin, lead, zinc or aluminium or alloys by oxidation of the metal. For higher melting point metals such as steel, oxidized impurities melt and float making them easy to pour off.The term dross derives from the Old English word dros, meaning the scum produced when smelting metals (extracting them from their ores). By the 15th century it had come to refer to rubbish in general. Dregs, and the geological term druse are also thought to be etymologically related. Popular non-metalworking uses of the word are derogatory: