Degradation mechanisms of green lead glazes on Tang ceramics from Subashi Buddhist Temple

Green lead-glazed ceramics from the Tang-period Subashi Buddhist Temple site in Xinjiang exhibit pronounced alteration despite burial in an arid environment. Four fragments selected from 104 examined specimens were analysed by semi-quantitative μ-XRF, optical microscopy, cross-sectional SEM–EDS, and micro-Raman spectroscopy. The altered glazes display granular, acicular, laminated, and crack-associated morphologies, together with sample-dependent redistribution of Pb and Si. Raman fitting indicates non-uniform reorganization of the residual silicate network rather than a common polymerization trend. Mobilized Pb was leached from some altered regions but locally immobilized as a phase consistent with hydrocerussite in Sample No. 1, hydrocerussite in Samples Nos. 2 and 3, and phosgenite in Sample No. 4. Cracks, cavities, and firing-derived heterogeneities controlled fluid access and alteration-front geometry. These results indicate coupled glass-network alteration, short-range elemental transport, and secondary precipitation under conditions consistent with intermittent moisture–salt interaction in the weakly alkaline, salt-rich burial environment.