The term "Bronze Age" is a leftover from the early days of archaeology when archaeologists thought that the use of this alloy of copper, tin, and lead marked a distinct stage in human history. But the more they have learned about ancient societies, the less significant bronze seems to be. Ancient China is the exception. In Chinese archaeology we apply the term "Bronze Age'' to the centuries from about 1500BC to 200BC, because the archaeological record of that time is dominated by bronze artefacts. A royal tomb of about 1200 BC contained 1,600kg of bronze.
Nothing like this is known anywhere else in the ancient world. Tutankhamun was a Bronze Age king, but in the British Museum's 1972 exhibition, none of the exhibits were bronze (the chief materials were fine wood, alabaster, semiprecious stone, ivory, and gold). The difference must have to do with the abundance of metal ores. Copper and tin were scarce in ancient Egypt and Mesopotamia. China was rich in metal ores. Instead of building pyramids, Chinese kings supported bronze foundries because bronze very early became linked in their minds with their hopes for the afterlife.
The rituals for the most powerful spirits centred on offerings of food and wine presented in splendidly decorated bronze vessels. The metal industry of ancient China was driven by demand for these vessels.
The scale of the industry fostered the growth of a technology of unparalleled sophistication. The ways of shaping metals can be grouped into two categories, casting and hammering. Casting means shaping metal by pouring liquid metal into a mould. Hammering is a term for any process that stretches and deforms metal in the solid state. In antiquity perhaps the most crucial difference between these two processes was the amount of metal they consumed. The tins that we buy at the supermarket are made by hammering (ie. rolling or pressing or stamping) rather than by casting because hammering is the easiest way to make the metal economically thin. The same consideration operated even more strongly in antiquity. Hammering was cheap because it conserved metal; casting was extravagant. Metal workers in ancient Egypt were under pressure to conserve metal and thus to avoid casting. The Chinese metalworker had no such imperative.
The Chinese relied on casting to supply every feature of the finished bronze, not just its shape but also its decoration and inscription. The bronze caster who made a decorated bowl did not cast a bowl and then chisel decoration on the cold metal; he made a clay model of the bowl, complete with decoration, and then formed a mould on that model.
Around the sixth century BC however, Chinese casters began to exploit the section-mould process in a new way, for mass production of decoration. Until then it seems to have been standard practice for the caster to put on the clay model all the decoration that was to appear on the finished object. Furthermore if he wished to cast a set of two matching bronze vessels, he made two matching models and formed one mould on each. He did not make one model and form several moulds on it, thus efficiently producing identical vessels, instead he laboriously carved independent models and produced almost identical vessels. This strangely inefficient way of work reminds us that in antiquity we cannot assume a concern for efficiency. Thus it is of great interest when in the sixth century we find signs of a concern for efficiency. And it is interesting that when production suddenly was made efficient, the key was not what we might expect - using one decorated model to make several decorated moulds - but something far more difficult.
The new technique is seen on a set of fifth-century BC bells in the British Museum's exhibition. Each bell was cast in a mould that had been formed on a clay model and removed from the model in sections, but with one key difference: the model was not decorated. The caster instead used an undecorated model to form undecorated mould sections, and then decorated the interior surfaces of the mould sections. It is here that the element of mass production entered. If the caster had carved the decoration on the model, he would have had to carve all the decoration. Instead he carved one small unit of each pattern on a clay block of its own, a block afterwards baked hard so that it could be used repeatedly. To decorate the mould, he smeared a thin layer of wet clay on the block and then peeled it off, bearing an impression of the pattern unit; this clay impression could be bent, trimmed, and laid into the mould section. Thus the interior walls of the mould were wallpapered with soft clay negatives taken from reusable pattern blocks. Not only did this save having to carve the decoration of the object to be cast; the blocks bearing the pattern units could be reused on other moulds.
The bronze foundries were part of the gradual rise of factory organisation, and in the centuries following the Bronze Age we find the same organisation spreading to other crafts, such as iron casting, ceramics, perhaps even printing. Large workshops with minute division of labour, something that amazed 18th-century European visitors to the Chinese imperial porcelain kilns, are perhaps the major legacy of the Chinese Bronze Age.