Non-invasive pigment identification at the Yungang Grottoes (Caves 7–8): a chemically corroborated spectral library
Abstract
Abstract Cultural relics constitute a precious part of human cultural heritage, making the early and comprehensive recording of their digital information increasingly urgent. Pigment identification on painted relics, however, remains hampered by scarce reference spectral databases, by library construction and validation protocols ill-suited to the task, and by the absence of site-specific pigment libraries. Here we construct a three-tier reflectance spectral library for Caves 7 and 8 of the Yungang Grottoes (Datong, China), combining commercial pigment standards, references migrated from public libraries and a Yungang-specific archive. In situ point spectra are matched within colour families against the library using a weighted score combining spectral angle mapping (SAM) and Euclidean distance, converted into a graded decision via two thresholds. Migrating the reference spectra increased gypsum re-identification from 0/15 to 14/15. On chemically confirmed reference points, pigment-group accuracy under leave-one-out re-fitting was 88.0% (95% confidence interval (CI) 78.7–93.6%), and the high-confidence zone covered 40.0% of points with no errors. Raman spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) revealed later interventions, including repainting containing emerald green. We thus establish a pigment classification and distribution survey of Caves 7-8, yielding a unified pigment inventory, and complete the application by…
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