A Raman spectroscopic study of heat-treated nephrite

Abstract

This study concerns the detection of heated nephrite jade, as some issues remain debatable: was heat-treatment used to facilitate jade carving or to modify jade's colour in ancient China? Has jade been burnt during funeral ceremony? Have forgeries been heat-treated to give the appearance of naturally weathered and altered jades? The understanding of the effect of heat on nephrite can provide useful information for answering these questions. Nephrite breaks down when heated above 840°C, and the phase transition is easily identified. However, detecting nephrite heated below 800°C was a challenging task as no principle crystal phase transition occurs. In this work, Raman spectroscopy is employed to study heated nephrite in a nondestructive way. For the first time, the subtle changes of molecular structure of nephrite heated below 840°C are reported in detail. The results show that the oxidation–dehydrogenation phenomenon is the key to understand the modification in heated nephrite.

Keywords:

• Jade
• Nephrite
• Raman spectroscopy
• Oxidation-dehydrogenation
• Heating effect
• Cation distribution

Acknowledgements

The author would like to thank the following people for their help on this project: J.-P. Desroches and H.-C. Tsao, curators of the Guiment Asian Museum in Paris, and M. Menu, head of Research Department of C2RMF (Centre de Recherche et de Restauration des Musées de France), for their support of the study of Chinese jade; W.-Q. He and Y.-F. Xiong, scientists of the Research Laboratory of Shanghai Museum, for providing raw reference of Jades; S. Pagès, scientist of C2RMF, for the technical help in Raman spectroscopy.