Bronze 青铜 and brass 黄铜
Bronze (qingtong 青铜) and brass (huangtong 黄铜) are the two widely used alloys in which copper is the main component.
Bronze is a copper alloy. Its composition varies, but its qualifying characteristics are greater harness than copper, which is a relatively soft metal, and good casting qualities.
The alloying metal is added in a contingent between 5% and 20%. The component that hardens the alloy is typically arsenic in early bronzes and tin from the “mature” bronze age. Arsenic bronzes play only a very minor role in East Asia and can be neglected for the region studied here.
Copper metallurgy thus employs copper, which often contains small amounts of gold, silver, lead and iron from ores and fluxes, and tin, which typically is not found in or in conjunction with copper deposits, bronzes.
Bronze objects are almost always cast, i.e. the metal is melted and cast into moulds in the molten state to achieve the desired shape.
Bronze was the material from which all ancient ritual objects are made and remained the material of highest cultural standing in East Asia.
Brass is an alloy of copper, zinc, and often some more metals in small quantities. It occurs early but remained exceedingly rare down to the 14th century in India, to the 16th century in China, and to the 18th century in Europe. The reason is that metallic zinc cannot be obtained from ore by smelting processes as they are employed for other metals because of its low melting (419.5 °C) and boiling points (907 °C). This means that at temperatures necessary to transform unwanted rock in the ore into liquid slag, the zinc has already escaped with the fumes.
Before zinc distillation enabled metallurgists to recapture the vaporised zinc, the only way to produce brass was heating relatively pure copper with special zinc ores. These were called calamine (yangnaoshi 羊脑石), a group of zinc ores that contain no sulphates, such as zinc carbonate ZnCO3 or smithsonite and zinc silicate Zn4Si2O7(OH)2·H2O or hemimorphite.
Smelting in closed crucibles or retorts permitted the production of metallic tin. The technology is first found in India, where crucible smelting had a long tradition (The famous Wootz steel was smelted in crucibles since the 6th century BCE).
The beginnings of zinc distillation in China are not documented. Chen Hailian dates widespread use of the technology to about 1500 (2017, ch. 2) using materials that reflect that brass was taking over from bronze for objects in everyday use. The hard date is 1580, when coinage shifted from bronze to brass (to save money on raw materials).
The use of the terms woqian 倭铅 and baiqian 白铅 that differentiated zinc from lead documents the presence of metallic zinc, which is similar to lead at first sight.
Brass contains up to 40% zinc. It is shiny and golden when high in zinc and more reddish when containing more copper. It is harder than copper but not much, and can be cast or hammered into shape. Brass utensils for everything from locks and furniture fittings, kettles and stoves, pipe ends and candlesticks became very widespread in late Ming and Qing China. Besides, the cash coins that the Qing mints cast in huge quantities from the 18th to the mid-19th century were brass coins made to look like bronze by adding tin and lead.
