基于拉曼光谱鉴定世界遗产大足卧佛颜料及相关研究

doi:10.3964/j.issn.1000-0593(2020)10-3199-06

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Abstract Niche of Sakyamuni Eentering Nirvana (Sleeping Buddha) at Baoding mountain, Dazu District, Chongqing, is the largest statue in Dazu rock carvings, one of the world cultural heritage, and also the world’s largest Buddha statue featuring only the upper part of the body. Suffered from the influence of natural power and human factors for thousands of years, various diseases such as paint scaling and biological colonization appeared on the surface of the Sleeping Buddha. To achieve the conservation and restoration of “raw materials and original technology”, it is necessary to identify the pigments of the statue. The surface pigments and the priming coat material of the Buddha were identified by means of micro-Raman spectroscopy (μ-Raman) and other techniques. Furthermore, the possible sources of white and green pigments, the relationship between pigment types and mildew have been discussed. The experimental results have shown that the back of each surface pigment of the Sleeping Buddha based on white priming coat material. The Raman spectrum of the priming coat material shows an intense band at 1 006 cm^-1 without other additional bands, which is the characteristic band of gypsum, that indicated the primer material is gypsum (CaSO₄·2H₂O) with high-purity. The surface of the statue is decorated with red, blue, white, and green pigments. The red was identified to be red ochre (Fe₂O₃), with stable property and widely used in various painted relics, such as murals and painted pottery. Combined analysis by polarized light microscopy, the blue was identified to be synthetic ultramarine blue (Na_6-10Al₆Si₆O₂₄S_2-4), with uniform particles and averaging less than 5 μm in diameter. The white was identified to be a mixture of cerussite lead white (PbCO₃) and mimetesite (Pb₅(AsO₄)₃Cl). Among white pigments, lead white is common, while mimetesite is infrequent. In particular, mimetesite is discovered as pigment for the first time at Dazu rock carvings. The Raman spectrum of green pigment displays intense bands at 859 cm^-1, attributed to the AsO^-₄ stretching vibration. The green was identified to be lavendulan (NaCaCu₅(AsO₄)₄Cl·5H₂O). The green pigment lavendulan and white pigment Mimetesite belong to arsenate, which is a rare secondary mineral. These pigments may be converted from other pigments. Among these kinds of pigments of Sleeping Buddha, the blue and red pigments are apt to mildew, especially blue, while the green and white pigments containing lead, copper, and arsenic are almost free from mold. It is speculated that this phenomenon may be related to the strong toxicity of heavy metallic salts of lead, copper, and arsenic. It has been pointed out that there are differences in the effects of different pigments on microbial activity. The research provides a scientific basis for pigment identification, restoration material selection and scientific conservation of Dazu Rock Carvings.

Key words：Micro-Raman spectroscopy; Pigment; Sleeping Buddha at Dazu Rock Carvings; Relics conservation; Material analysis

Received: 2020-01-13 Accepted: 2020-05-05

ZTFLH:

O657.37

Corresponding Authors: WANG Li-qin E-mail: wangliqin@nwu.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2020)10-3199-06 OR https://www.gpxygpfx.com/EN/Y2020/V40/I10/3199