Identification of Clay Mineral Jade with Dyed Yellow Skin to Imitate Tianhuang

Driven by financial benefit, the market is filled with Tianhuang imitations. In this study, different imitations of Tianhuang that have been artificially treated (skinned and dyed) are selected as the research objects. Gem microscope, FTIR, UV-Vis spectra and XRF tests are performed to explore the method for non-destructive identification of Tianhuang imitations. The results show that the colour distribution of the skin and the internal, the surface pit morphology, and the surface luster of dyed imitation samples are different from natural Tianhuang. Infrared spectra indicate that the main components of imitations with yellow skin are diopside, illite, chlorite and kaolinite. Analysis of first and second derivatives of ultraviolet-visible diffuse reflectance spectroscopy (DRS) and first and second derivatives after K-M transformation reveals that natural yellow skin Tianhuang has peaks corresponding to hematite and goethite, while the yellow skin of dyed imitations does not show similar peaks. XRF testing results reveal abnormal enrichment of Pb elements in the dyed yellow skin of Tianhuang imitations.