Investigating Bronze Casting Production in Chu’s Western Borderlands during the late Warring States Period (c.306–221 BC): A case study of metallurgical materials excavated from tomb M19 of the Wangbao cemetery in Hunan, China

The Wangbao cemetery (王堡墓地) is a burial site associated with the Sifangcheng settlement in Baojing County, Hunan Province, with tombs from the late Warring States period (306–221 BC) exhibiting typical Chu features. Analysis of the metallurgical materials excavated from tomb M19, suggests that bronze casting activities may have occurred at Sifangcheng during this period, with two types of alloys identified: lead–tin bronze and tin bronze. The lead isotope ratios of samples BJ-22, BJ-26, BJ-23, BJ-24, BJ-25, and BJ-27 indicate the likely sources of the lead material, suggesting it was sourced from areas in western Henan or western Hunan. The lead isotope ratio of sample BJ-21 indicates that the source of the copper material is likely close to the copper mines along the Yangtze River in present Jiangxi and Hubei provinces. Based on existing literature and research, it is likely that the tin materials used in western Hunan originated in the southern region of the Nanling Mountains. Being located in Chu’s western borderlands during the mid to late Warring States period (391–221 BC), a relatively complete bronze production system, including mining, smelting, and casting, has been established in the western Hunan region. Among these, the metallurgical artifacts from Wangbao M19 not only directly reflect the technological aspects of bronze production in the middle reaches of the Youshui River, but also serve as a concrete manifestation of the Chu state’s development and control over its western frontier during this period.