Smelting is a pyrometallurgical process used to separate metal from ore through heating above the melting point. In matte smelting, the metal separates as a sulfide matte along with slag, while in reduction smelting the metal separates as a liquid. Flash smelting combines roasting and smelting for more efficient processing of sulfur dioxide off-gas. Converting processes further purify molten metal from smelting by oxidizing impurities in the presence of air or oxygen, producing high purity metal and slag. Early processes like puddling and cementation produced wrought iron and blister steel respectively but were inefficient.