Characterizing ancient jade by on-site analysis in Sanxingdui, China

Abstract

Characterized by various materials, types and patterns, ancient jade is a unique symbol of Chinese civilization. However, crucial information can be jeopardized by the sudden exposure during excavations, and abundant jade artefacts were stored without scientific identification in the archaeological context. Sanxingdui site was an essential center of a complex society in the Chengdu Plain in Bronze Age China. During the new excavation in Sanxingdui sacrificial area (pit K3–K8) since 2019, cabins have been used for better site conservation, providing ideal conditions for on-site study. Employing portable devices, on-site non-destructive analysis were conducted inside pit K8. The results of Raman and XRF show that the raw material is nephrite, indicating the consistency of jade material preference with the majority of Sanxingdui jade from pit K1–K2 and the majority of prehistoric jade as well. Evidence of mineral thermal phase transition from tremolite to diopside was found on the zao chisel and proved the existence of jade burning related to the sacrificial activities. The Fe content in the surrounding soil led to the red and orange colors on the jade surfaces and the neutral environment helped retaining of the original texture and natural luster of the nephrite. Based on the geometric morphometric database, the jade zhang forked blade was quantitatively recognized as the most typical zhang type only found in Sanxingdui. It is demonstrated that the non-destructive analysis is efficient to characterize the ancient jade and makes it possible to construct the database of all the jade artefacts on site, providing the basis of solving larger-scale archaeological problems that are not necessarily bounded by geographical regions or time periods.