Metallurgy

Materials science

Alloy

Archaeology

Ancient history

Zinc

Buddhism

China

History of China

Copper

History

Brass

Heritage Science

This paper surveys of the chemical composition of the copper alloy coinage in China from the Qin Dynasty to the end of the Yuan Dynasty (221 BCE–1368 CE). It shows a dramatic change in the alloying practice used to cast these coins from the Qin unification (after 221 BCE), compared to that practiced in the pre-Qin. There are a number of shifts in the quality of the coinage from dynasty to dynasty, such as the obvious debasement of the Southern Song coinage (1127–1279 CE) when compared to that of the previous Northern Song dynasty (960–1127 CE). Particular attention is paid to the low levels of zinc in the coinage over the period. Although not as obvious as the switch to brass coinage in the Ming, certain periods do show occasional values of zinc up to 2–4%, which we suggest could reflect the sporadic input of recycled brass (Cu–Zn alloy) into the raw material melt. There were several major suppressions of Buddhism during this period, when Buddhist brass statuary was recycled into the coinage, providing a plausible mechanism for the injection of small quantities of zinc into the coinage alloy. A diachronic study of the amounts of iron in the metal, taken to indicate changes to the manufacturing process of copper, also show changes over time. The median levels of iron jump from the Qin (221–206 BCE) to the Western Han (206 BCE–9 CE), possibly reflecting the adoption of slagging processes in the production of the copper, followed by a gradual decline to the Northern Song (960–1127 CE), and a rapid increase during the Southern Song (1127–1279 CE). Finally, a study of changes in the content of silver over time reveals differences in the sources of lead, or changes in lead and silver extraction technologies, over the period.

Chemical studies of Chinese coinage II: from Qin to Yuan (221 BCE–1368 CE)