Transmission and innovation on gold granulation: the application of tin for soldering techniques in ancient China

Granulation, an ancient metal processing technique mainly applied to gold, has originated from West Asia, and later appeared at many different archaeological sites across the Eurasia. The distribution of granulated gold ornaments bearing diverse soldering techniques reveal the long-distance human interaction across the Eurasia. This paper presents the scientific analysis of the surface morphology and elemental composition of two granulated gold ornaments from Tushan Tomb No.2 pit in Xuzhou, Jiangsu Province, which approximately dated to the first century CE of Han Dynasty. Multiple non-destructive analytical methods including Ultra-Depth Three-Dimensional Microscope, Energy dispersive X-ray fluorescence spectrometer (XRF) and Scanning electron microscope with energy dispersive X-Ray spectrometer (SEM-EDS) were conducted to obtain analytical data. The result indicates that tin-participated soldering technique has been adopted to accomplish the granulation. Although the usage of tin has been mentioned in a former study as "a secret of Etruscan granulation", the lack of quantitative analyses leaves this assumption unconvinced. Our findings on Tushan ornaments throw light on this issue by illustrating the regular distribution pattern of the tin content at the joints, which appears to be intentionally added for certain amount. Although tiny in size, the gold granules record the secret of soldering techniques used in China and many other regions across the Eurasia during the ancient time, complementing the study of granulation techniques and reflecting the transmission and innovation along with the technological and cultural contacts.