Complementary analytical methods in identifying gilding and painting techniques of ancient clay-based polychromic sculptures

The gilding and painting techniques for the clay-based polychromic sculptures in Jizo Hall of Chongqing Temple, Shanxi Province of China, are analyzed by complementary techniques of microscopy, environmental scanning electron microscopy (ESEM), energy dispersive X-ray mapping (EDX), micro-Raman spectroscopy (μ-RS), and Fourier transform infrared spectroscopy (FTIR) with a reasonable sequence. 7 gilded samples and 6 pigmented samples are collected from Jizo Hall. For the 7 gilded polychromic samples, drying oil-based, Chinese lacquer-based and glue-based “Jin Jiao” techniques are identified respectively according to their different adhesive layers used for jointing gold leaf to the preparation layer. But the presence of a copper foil top surface, as well as the inner layers with crocoites (PbCrO4) and modern red pigment in one alleged gilded polychromic sample indicate a later restoration work. Among them, two gold layers have been identified in 4 samples due to the regilded work in history. For 6 pigmented samples, painting layer is generally applied on a white preparation layer made of kaolinite or the mixture of kaolinite and gypsum. Atacamite, cinnabar, minium, yellow ochre and gypsum are identified as the main pigments, and the protein-based material is confirmed as the binding medium for red pigments. This research not only reveals the Chinese traditional gilding and painting techniques employed in polychromic sculptures of Jizo Hall, but also demonstrates the advantages and limitations of each analytical technique for identifying polychromic samples, and the necessity of complementary analytical techniques approach.