684 metallurgy: Greece For warriors, this meant not only durable armor but weapons that were less likely to break under stress GREECE BY J OHN W HUMPHREY As early as the second half of the Neolithic Age (ca 5000–ca 3000 b.c.e.), people began to work soft native metals such as copper and gold, which they could form into shapes by hammering with traditional stone tools; hence this period is called the Chalcolithic, or Copper Age But the shapes of these items were so limited and the malleability of the native metals so high that they could not be used as functioning tools or weapons The discovery of primitive casting techniques produced more functional shapes, but the off-gassing of molten copper restricted the casting to open, one-piece molds of sandstone or clay, so this technique left one flat surface on the tool and used much precious metal By the Bronze Age (ca 2800–700 b.c.e.) kilns designed originally for firing ceramics produced temperatures high enough (about 2000 degrees Fahrenheit) to smelt copper from its carbonate and oxide ores It seems likely that copperbased pigments used to decorate ceramics were accidentally smelted in pottery kilns, leaving behind beads of pure copper This copper was then combined with arsenic or tin to produce bronze, a metal superior to copper because of its lower melting point, ease of casting, and hardness The invention of two-piece molds then allowed symmetrical tools to be cast, and it saved metal because a removable core could be inserted into the mold to create a hollow object Such metal tools had several advantages over those of stone: They were thinner, sharper, and more durable; they allowed a greater variety of forms; and they could be reworked when dull or broken The processing of ore to extract the desired metal generally followed a common procedure, though some stages were omitted for certain metals What follows is applicable to ores of copper, tin, and lead/silver, but not gold (which was always available naturally in its pure form) or iron Because most ores contain sulfur or oxygen, the fi rst requirement is to separate these from the desired metal Th is was done in a simple roasting oven, in which the ore was layered with the fuel (usually charcoal), covered with a temporary shell, and burned in a reducing atmosphere; the carbon combined with the sulfur or oxygen and gassed off, leaving the desired metal behind, though still combined with impurities The ore was then broken up by crushing it either in mortars with an iron pestle or in mills that resembled the large “hourglass” grain mills familiar from Pompeii and Ostia The crumbles were then either sieved or, more commonly, washed to remove the unwanted gangue (surrounding rock), which, because it was heavier than the metal, was left behind on the washing table This process is well known from the surviving washing tables at Laurion, Greece, which ingeniously used recirculated water The remaining concentrated ore was then heated in a smelting furnace with sufficient temperature to produce a molten metal that separated from the unwanted slag; the two would generally be tapped off at different heights according to their specific gravities Th ree elements were required for this procedure: a furnace, suitable fuel, and a supply of forced air Open hearths were fi rst used as furnaces, but they proved unsatisfactory because they could not sustain the necessary temperatures However, in classical shaft furnaces, like those used for fi ring pottery, the charcoal and ore could be properly layered and the heat concentrated within the restricted space The preferred fuel was charcoal, the only material that could generate sufficient and continuous heat for smelting Other fuels were tried—wood (before the deforestation of the Mediterranean), lignite coal, and even dried dung—but with little success The Greeks (like their Egyptian predecessors in the Bronze Age) used bellows to provide a constant supply of forced air to maintain the necessary temperature for smelting copper, though pipettes were used for smaller quantities of precious metals These bellows were generally fabricated from the skins of animals, with flaps of skin serving as inlet and outlet valves and terra-cotta nozzles to protect them from the heat of the fire These bellows were often used in pairs and operated by foot to produce a constant flow of air Once the metal had been tapped off, it was usually allowed to cool and solidify into ingots before being remelted and cast Only occasionally did the casting of a final product seem to have been done directly from the smelting stage Before being worked into its desired form, silver was subject to further refining by cupellation: The smelted ore was placed in a porous clay crucible and heated; the residual lead was Gold mask from Mycenae (Alison Frantz Photographic Collection, American School of Classical Studies at Athens)