Improvement and integration: scientific analyses of willow-leaf shaped bronze swords excavated from the Shuangyuan Village Cemetery, Chengdu, China

Willow-leaf shaped sword is a kind of exclusive bronze weapon popular only in the states of Ba and Shu during the Eastern Zhou Dynasty (770-256 BC). Its prototype may originate from Central Asia and India and is a typical example of a trans-regional and cross-cultural artifact. Here, we present a scientific study of willow-leaf shaped swords of Shu State from the Shuangyuan Village Cemetery, Chengdu, by pXRF and MC-ICP-MS, and attempted to argue for the improvement and integration of weapon production in Shu by characterizing its elemental composition and lead isotopic signature. The results show that there is a significant difference in the tin content and lead material source between the Ba and Shu bronze swords. This feature can be applied as an important indicator to distinguish willow-leaf shaped swords from Ba and Shu, especially when the appearances are almost confused. The alloy formula of the Shu bronze sword was influenced by the bronze-making technology of Chu and other states. Combining the published lead isotope data of the willow-shaped bronze swords, it can be inferred that Shu State has produced bronze weapons with considerable frequency and in many batches, which was a major motivation for triggering faster progress in its craft.