Degradation of Emerald Green: Scientific Studies on Multi-polychrome Vairocana Statue in Dazu Rock Carvings, Chongqing, China

Researchers have identified the degradation products of emerald green and cerussite, two historically used pigments, in the multi-polychrome Vairocana Statue at Dazu Rock Carvings. The study reveals that lavendulan (NaCaCu5(AsO4)4Cl·5H2O) and mimetite (Pb5(AsO4)3Cl) form through complex chemical processes involving the degradation of emerald green (Cu(C2H3O2)2·3Cu(AsO2)2) and cerussite (PbCO3), oxidation of arsenite, migration of arsenate, and precipitation reactions influenced by environmental conditions. The analysis of paint cross-sections using optical microscopy, Raman spectroscopy, SEM–EDS, and mapping also indicates that the statue's paintings were executed at least four times, with the most recent layer possibly dating to after 1850s. This finding highlights the importance of understanding pigment degradation in complex environments for heritage conservation.

Li, Z., Wang, L., Chen, H., & Ma, Q. (2020). Degradation of Emerald Green: Scientific Studies on Multi-polychrome Vairocana Statue in Dazu Rock Carvings, Chongqing, China. https://doi.org/10.21203/rs.2.23940/v1