Copper alloy production in the Warring States period (475-221 BCE) of the Shu state: a metallurgical study on copper alloy objects of the Baishoulu cemetery in Chengdu, China

Abstract

Many bronze objects were unearthed in the capital of the Shu state in present-day Chengdu. However, only a few metallurgical studies have been carried out on those objects. This research attempts to study the alloy techniques and possible ore sources of 28 bronze objects recently excavated from the Baishoulu cemetery in Chengdu. Elemental composition and lead isotope ratios were measured, and metallographic observations were conducted. The results indicate that most objects were copper–tin–lead alloys with variable tin and lead content. The samples showed evidence of casting, as well as cold working and annealing techniques. The lead isotope data indicate that multiple lead sources were used in Baishoulu; however, the exact number is not yet known. Most of the lead sources in Baishoulu are the same as those in Zeng state bronze and Chu state bronze. In addition, some of the bronzes came from sources that were widely used in the Central Plains and surrounding regions. This new information aids in understanding the cultural interactions between Shu and other states. Moreover, some bronzes might have used local lead sources. Copper and tin sources were difficult to determine; however, the different trace elemental patterns between Baishoulu and Bayilu bronzes indicate different copper and tin sources might be used. Additionally, copper and lead may originate from different sources in the Shu state. Systematic data are necessary to disclose a possible metal source exchange network involving the Shu state in the Warring States period.