Bronze Age Casting
The ability to make bronze tools, weapons, and ritual vessels was such a significant advancement in world civilization that it lends its name to an entire era: the Bronze Age. The skill and resources needed to fabricate bronze were in place in ancient China by 1700 BCE, over a thousand years later than in Egypt, Mesopotamia, and India. The earliest Chinese bronze artifacts have been traced to the Erlitou culture in Henan province. Their discovery confirms foundries for smelting and casting metal were active in northern China between 1300 and 900 BCE, a highpoint of early Chinese casting.
Making bronze requires two things: copper and tin ores, sometimes mixed with lead; and intense heat for refining and casting. Chinese founders made their metal objects using clay for both models and removable section molds. (This differs from the Mediterranean and European practice of casting objects using wax-covered models.) After a desired vessel was fashioned from clay, it was covered with an additional layer of clay that, when dried, was carefully cut away in matching vertical sections (usually three or four) to create the casting molds. The original clay model was then shaved down for the interior core, and the mold sections were reassembled around it to make the outer walls. The space between the core and outer molds was then filled with molten bronze. In many cases, the joins between mold sections appear as raised ribs on the exterior of finished bronzes. After the bronze cooled, the clay molds were broken and removed, and the vessel was polished to take away flaws and any metal that had seeped into gaps between the mold sections.