Feasibility studies of Sn isotope composition for provenancing ancient bronzes

This study examined isotope fractionation during bronze casting and assessed variation in Sn isotope composition of Chinese bronze products to ascertain whether a Sn isotope tracer is applicable to provenance studies of bronze products or not. A casting experiment revealed that the Sn isotope composition of a bronze block surface becomes slightly heavier, 0.22‰ in δ124Sn/120Sn scale, (δ124Sn/120Sn = [(124Sn/120Snsample)/(124Sn/120Snstandard)−1] × 103), than original Sn beads because of selective evaporation of light isotopes. The Sn isotope compositions of six bronze product samples excavated in China were analyzed. The variation of δ124Sn/120Sn in the six samples was as great as 0.4‰. Six bronze samples showed small but detectable isotope variation that surpassed isotope shift during casting. Results suggested that the application of Sn isotope ratio to provenance studies of bronze products was of limited use because of the small variation. However, it was also shown that the Sn isotope ratio can be applied for provenancing a bronze sample with a distinct isotope composition.