The process of separating metal from ore. In most cases, this is done by heating in a furnace or hearth. Some metals may melt whilst being smelted, but this is not necessarily part of the process. The main chemical reaction in smelting most of the ores used in antiquity is that of reducing a metal oxide. If the ore was not already in the oxide form, then it was converted by a preliminary process. Most ancient copper probably came from oxide ores, which could be smelted by heating with charcoal. The temperature at which the copper oxide was reduced could have been as low as 800°C — the kind of temperature reached in a simple hearth or kiln. In many cases, however, the copper was melted into ingots during the smelting operation. This requires a temperature of some 1083°C, which would have necessitated the use of a furnace or hearth assisted by bellows. Careful control of the amount of air entering the furnace would be required for successful smelting. Similar, or lower temperatures would be required for the smelting and melting of gold, silver, lead and tin, but the melting point of iron is 1540°C, beyond the range of a simple furnace. Iron could, however, be smelted. The reduction of iron oxide ores can take place at 800°C. If the temperature is increased to some 1150°C, the slag melts and can be drained off. This leaves a spongy bloom of iron and remaining slag inclusions. The slag within the bloom must then be removed by forging. Remains of the smelting process include ingots, slag, tuyères, hearths containing slag and cinder, and more sophisticated furnaces. See also iron and steel.
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983Copied