History. Historically, the first smelting processes used carbon (in the form of charcoal) to reduce the oxides of tin (cassiteriteHistorically, the first smelting processes used carbon (in the form of charcoal) to reduce the oxides of tin (cassiterite, SnO2), copper (cuprite, CuO) and lead (Lead(II) oxide, PbO), and eventually iron (hematite, Fe2O3) In all these reactions the reducing agent was actually carbon monoxide, as the charcoal and oxides remained solid and therefore could not react directly with each other. For copper and lead, important ores were actually the sulfides, chalcocite (CuS2) and galena (PbS); these first had to be converted to oxides by roasting them in air Silver was generally found in the form of sulfides mixed with galena; it was smelted together with lead and was afterwards separated from it by cupellation. The primary source of mercury was the sulfide ore (cinnabar, HgS). This was roasted to produce the oxide HgO, which decomposed into oxygen and mercury, which both left the furnace as a (highly toxic) vapor, that was condensed in appropriate containers. In the Old World, humans learned to smelt metals in prehistoric times, more than 8000 years ago. The discovery and use of the “useful” metals – copper and bronze at first, then iron a few millennia later – had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into Stone Age, Bronze Age, and Iron Age. In the Americas, the Incas and other civilizations of the Andes had mastered the smelting of copper and bronze by the time the first Europeans arrived in the 16th century.
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