Analysis on the Spectroscopic Characteristic and Processing Technique of Crystal Bead Ornaments Excavated from the Xiongjiazhong Tomb in Jingzhou, Hubei Province

The Xiongjiazhong tomb located in Jingzhou, Hubei Province, represents the highest-ranking aristocratic burial site from the Chu State discovered to date. The number of jade artifacts excavated from the tomb has now exceeded 3 000 pieces, covering a variety of materials including tremolite, talc, serpentinite, agate, and crystal. This study focuses on 8 crystal bead ornaments excavated from tomb NPM12 to investigate their processing techniques and potential provenance. The non-destructive testing methods such as infrared spectroscopy, Raman spectroscopy, and ultra-depth-of-field microscopy were used for comprehensive analysis of the crystal bead ornaments. The infrared spectroscopy test results revealed that the spectral peaks of the bead samples are consistent with the standard infrared spectrum of crystal. Raman spectroscopic examination detected not only the dominant quartz signatures but also hematite inclusions. Ultra-depth microscopic observations demonstrate the crafting technique of the crystal bead ornaments: (1) The drilling is divided into two stages, with noticeable misalignment at the junction. The boreholes are conical cylindrical perforations with a diameter of 1.5-3.0 mm, clear concentric spiral striations can be observed inside. It is a typical double-sided drilling process, which is completed by cylindrical tube drilling tool with jade cutting abrasive; (2)The distinct directional grinding traces on the terminal surfaces of the samples are accompanied by micro-pits and punctate texturing along the lateral facets. These morphological features suggest that the Chu artisans had developed specialized polishing techniques for processing high Mohs-scale materials, particularly quartz. Through studying the colour and inclusions characteristics of the crystal beads, and crystallographic orientation and extraction angles, it is concluded that 6 amethyst beads are originated from the same amethyst deposit with well-developed rhombohedral faces. The study also indicates that these crystal bead ornaments were likely imported from the Qi State to the Chu State. This finding offers valuable insights into material selection and crafting techniques employed by the ancient Chu ancestors, and provides important references for understanding the cultural exchanges and interations between Chu Culture and its neighboring regions in archaeology research.