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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摘要：重庆大足宝顶山释迦牟尼涅槃圣迹图（即卧佛）是世界文化遗产大足石刻群中最大的一尊造像，亦是世界最大的石雕半身卧佛像。在千百年自然营力和人为因素的影响下，大足卧佛表面出现了颜料脱落、霉变滋生等多种病害。为了实现“原材料、原工艺”的保护修复，需要对颜料成分进行分析鉴定。利用显微拉曼光谱（μ-Raman）等技术对佛像表面的颜料和打底材料进行了分析鉴定，同时探讨了其中白色颜料、绿色颜料的可能来源及颜料种类与霉变的关系。实验结果表明：卧佛表面每种彩绘颜料背面均以白色物质打底，打底材料的拉曼光谱在1 006 cm^-1处存在强特征峰，与石膏峰位及强度匹配度极高，且杂质峰少，鉴定打底材料是较高纯度的石膏（CaSO₄·2H₂O）。表面装饰有红、蓝、白、绿等彩绘颜料，其中红色颜料为常见颜料土红（Fe₂O₃），其性质稳定，广泛使用在壁画、彩绘陶器等各类彩绘文物中；结合偏光显微分析鉴定出蓝色颜料为人工合成颜料群青（Na_6-10Al₆Si₆O₂₄S_2-4），其颗粒均匀、粒度一般＜5 μm；白色为常用颜料碳酸铅式铅白（PbCO₃）和罕见颜料砷铅矿（Pb₅(AsO₄)₃Cl）的混合物，砷铅矿作为颜料在大足石刻属首次发现；绿色颜料在859 cm^-1处出现最强特征峰，是AsO^-₄伸缩振动产生的，鉴定绿色颜料为少见的氯砷钠铜石（NaCaCu₅(AsO₄)₄Cl·5H₂O）。大足卧佛绿色颜料氯砷钠铜石和白色颜料砷铅矿均属于砷酸盐类物质，其矿物属于自然界中稀少的次生矿，这些颜料可能是由其他颜料转化而来。在大足卧佛的各色颜料中，蓝色和红色颜料更易滋生霉斑，特别是蓝色颜料长霉最为严重，而含铅铜砷的绿色和白色颜料表面几乎不长霉，推测可能与铅、铜重金属盐和砷元素的强毒性有关，并指出不同颜料对微生物活性的影响存在差异，该研究为大足石刻彩绘颜料鉴定、修复材料选择及保护修缮提供了科学依据。

关键词：拉曼光谱；颜料；大足卧佛；文物保护；材质分析

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

收稿日期: 2020-01-13 修订日期: 2020-05-05

中图分类号:

O657.37

基金资助: 国家自然科学基金项目（21175104），陕西省重点研发计划项目（2019ZDLSF07-05），西北大学文化遗产学院研究生创新项目（2019WYYCY-02）资助

通讯作者: 王丽琴 E-mail: wangliqin@nwu.edu.cn

作者简介: 王丽琴，女，1961年生，西北大学文化遗产学院教授 e-mail：wangliqin@nwu.edu.cn

引用本文:

王丽琴，马彦妮，张亚旭，赵星，何秋菊，郭金沂，任翰霆. 基于拉曼光谱鉴定世界遗产大足卧佛颜料及相关研究[J]. 光谱学与光谱分析, 2020, 40(10): 3199-3204.
WANG Li-qin, MA Yan-ni, ZHANG Ya-xu, ZHAO Xing, HE Qiu-ju, GUO Jin-yi, REN Han-ting. Pigment Identification of Sleeping Buddha at World Cultural Heritage Dazu Rock Carvings With μ-Raman Spectroscopy and Related Research. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(10): 3199-3204.

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