Multi-Spectroscopic Characterization Of Natural Organic Dyes In Ancient Wall Paintings ——Based On Kizil Cave Temples

Ancient wall paintings are important parts of cultural heritage.Research and protection are inseparable from the analysis of colorant,the main body of information.More and more scholars have paid attention to the use of not only mineral pigments also some natural organic dyes in ancient murals.However,there are few special analyses on the dyes in ancient murals.Highly sensitive,fast,non-destructive,and in-situ spectroscopy method for organic materials is the first choice for studying the use of natural organic dyes in ancient murals.In addition,investigating and analyzing natural organic dyes and their applications in the wall paintings of the Kizil Cave Temples in Xinjiang,China are the starting points and foothold of this research.Specifically,this experiment uses a combination of UV-VIS fiber optical reflectance spectroscopy（FORS,200-800nm）,fiber optical fluorescence spectroscopy（FOFS,200-800nm）,Fourier transform infrared spectroscopy（FTIR,400-4000cm-1）and near-infrared spectroscopy（NIRS,1600-2400nm）.Four spectral methods are more sensitive to the identification of organic colored materials（natural dyes）and can be used for in-situ,non-destructive analysis of cultural heritage.In order to evaluate the identification ability of the methodology,the simulated mural dye samples and their aging reference samples made by different techniques,such as direct application of dye solution,lake,mixing of dye solution with lime or gypsum powder,and mixing of inorganic and organic dyes,were used for data collection and statistical analysis.The analysis method is applied in practical cases（analysis of organic dyes and techniques in Kizil Cave Temples murals）to provide assistance for the material and technology confirmation of cultural heritage.According to relevant literature and research results,six dyes that may be used in the Kizil Cave Temples murals: indigo,lac dye,turmeric,madder,safflower,and gamboge,are selected as the representatives of the experimental research objects.After testing and analyzing the dye samples prepared by different techniques in the laboratory,it is found that fluorescence spectroscopy and UV-VIS reflectance spectroscopy are more effective methods to analyze the dye types and their using techniques.But all kinds of details should be taken into account in the identification of the same color dyes and the different techniques of same dyes.Fourier transform infrared spectroscopy and near-infrared spectroscopy may play a certain role in the identification of dye types,but the results are not as obvious as those of the first two spectroscopic methods.In a word,the combined use of four spectral analysis methods can achieve the primary purpose of identifying and analyzing the types of dyes and their use techniques,and it has been applied well in the murals of Kizil Cave Temples.