By Joseph A. McGeough
Metals and Smelting
The discovery that certain heavy “stones” did not respond to hammer blows by flaking or fracturing but were instead soft and remained intact as their shapes changed marked the end of the long Stone Age. Of the pure, or native, metals, gold and silver seem to have attracted attention at an early date, but both were too soft for tools. The first metals of value for toolmaking were natural copper and meteoric iron. Although they were scarce, they were tough and potentially versatile materials that were suited for new purposes, as well as many of the old. They also introduced a new problem, corrosion.
Copper occurs in native state in many parts of the world, sometimes in nuggets or lumps of convenient size. It is malleable; that is, it can be shaped by hammering while cold. This also hardens copper and allows it to carry a sharp edge, the hammered edge being capable of further improvement on an abrasive stone. After a certain amount of hammering (cold-working), copper becomes brittle, a condition that can be removed as often as necessary by heating the material and plunging it into cold water (quenching). The softening operation is known as annealing, and repeated annealing are necessary if much hammering is required for shaping.
Among early toolmakers, nuggets of copper were hammered into sheets, divided into strips, and then separated into pieces to be worked into arrowheads, knives, awls, choppers, and the like. Copper was also shaped by beating pieces of the soft metal into appropriately shaped rock cavities (moulds).
Meteoric iron, widely distributed but not in heavy deposits, was a highly prized material more difficult to fabricate than the softer copper. Its celestial origin was recognized by the ancients: the ancient Egyptians called it black copper from heaven, and the Sumerians denoted it by two characters representing heaven and fire.
Like copper, iron hardens under the hammer and will then take a superior edge. Iron can be annealed, but the process is quite different from that of copper because, with iron, slow cooling from a high temperature is necessary. Meteoric iron is practically carbonless and, hence, cannot be hardened in the manner of steel; a high nickel content of about 8 percent makes it relatively corrosion resistant.
For early toolmakers, small meteorites were the most convenient sources of iron, but larger bodies were hacked at with copper and rock tools to yield tool-sized pieces for knives, spear points, arrow points, axe heads, and other implements. Meteoric iron was beaten into tools in much the same way as copper, although it could not be forced into a mould in the manner of the softer metal. Much rarer than copper, meteoric iron also was often used for jewellery, attested to by burial finds of necklaces of iron and gold beads, iron rings along with gold rings, and ornaments in sheet form.