Smelting is chemistry, not melting, and it began with copper in Serbia
Getting metal out of rock is less about heat than about stealing oxygen. Carbon monoxide pulls oxygen atoms away from the ore, leaving pure metal behind. Humans first managed this with copper between 5500 and 5000 BC, at sites in what is now Serbia, and the trick eventually named whole ages of history.
Most ores are compounds in which a metal is locked up with oxygen, sulfur, or carbon and oxygen together. Simply melting them does nothing useful. Sulfide and carbonate ores are first roasted in air, which drives off sulfur as sulfur dioxide or carbon as carbon dioxide and leaves an oxide. Then comes reduction: in an air-starved furnace, burning carbon makes carbon monoxide, which grabs oxygen from the oxide and escapes as carbon dioxide. Iron oxide gives up its metal at about 1250 °C, nearly 300 degrees below the melting point of iron itself.
Helpers make the process cleaner. Fluxes such as lime bind sulfur, phosphorus and silicon impurities into slag that can be skimmed away, and the molten slag also blankets the hot metal so it cannot reoxidise. Aluminium refuses to cooperate at all: it holds oxygen more tightly than carbon does, and its oxide melts only at about 2,072 °C, so it is freed by electricity in a bath of molten cryolite instead. Modern copper smelters have largely abandoned huge reverberatory furnaces for flash smelting, which now accounts for over half of the world's copper plants.
The history is full of revised dates. Campfires fall roughly 200 degrees short of what copper needs, so the first smelting may have happened in pottery kilns. A copper mace head from Turkey was long thought the oldest, until closer study showed it had been hammered from native metal. Supposed lead beads from Çatalhöyük turned out to be lead-rich minerals rather than smelted lead. Bronze, harder than copper, followed around 3500 BC in Asia Minor.
Iron came later and slowly. Fragments from Kaman-Kalehöyük in Anatolia date to 2200 to 2000 BC, and during the New Hittite Empire iron tools were used by elites but not ordinary people. Early European and African ironworkers used bloomeries, which never got hot enough to melt iron, producing a spongy lump that had to be hammered into wrought iron. In the Andes, pre-Inca peoples mastered copper and silver independently, centuries before Europeans arrived, though never iron.
Source: Smelting
