Characterization of Dyes for Han Dynasty Wool Fabrics in Xinjiang by Time-of-Flight Secondary Ion Mass Spectrometry

In Xinjiang, China, a female corpse dating back to the Han Dynasty was discovered adorned in splendid attire crafted from wool fibers dyed in vibrant shades of red, blue, and light yellow. This study utilized fabric fragments as research specimens to analyze the dyes present, primarily employing time of flight secondary ion mass spectrometry (TOF-SIMS), in conjunction with optical microscopy, ultra-high performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) and a mercury vapor analyzer for precise characterization. The TOF-SIMS analysis revealed the presence of mercury isotopic ions (²⁰²Hg⁺ and ¹⁹⁹Hg⁺), mercury-sulfur ions (HgS⁺, m/z 234), sulfur isotopic ions (³²S⁻ and ³⁴S⁻) on the surface of the red fiber samples. These findings suggest the utilization of cinnabar (HgS), a naturally occurring inorganic mineral dye, in the red fibers. Moreover, mercury content measurements indicated a significant enrichment of mercury in the red fibers, with the Hg content of 84 ng/g, markedly higher than the average Hg content of other fibers, which stood at 31 ng/g. Analysis of the blue fiber samples detected the quasi-molecular ion m/z 263 (M+H⁺) and a series of reasonable fragment ions, such as m/z 235 (C₁₅H₁₁N₂O⁺) and m/z 247 (C₁₆H₁₁N₂O⁺), indicative of the presence of indigo, a natural plant-based organic dye. UPLC-HRMS analysis further confirmed the presence of indigo in the blue fabric samples, providing cross-validation of the dye used. The light yellow fiber samples did not yield detections of common organic dyes like turmeric or inorganic pigments such as iron-yellow (Fe₂O₃H₂O). The yellow hue observed in these fibers may be attributed to the natural aging of the original white wool, remaining undyed. Additionally, granular water-soluble inorganic ions such as NaCl, carbonate, and sulfate were detected within the yellow fabric samples. This study underscores the efficacy of the TOF-SIMS method for in-situ microanalysis and ultra-high sensitivity detection, rendering it is suitable for the analysis of both organic dye and inorganic dye. Moreover, TOF-SIMS will be widely used in archaeological and museum collections related research.