拉曼光谱和色差法在丝质文物色彩损伤评估中的比较

丝质文物是博物馆内的重要藏品之一，具有极高的文化、艺术、历史价值。作为一种性质不稳定的蛋白质有机构成材料，丝质文物极易受到光学辐射而发生泛黄等色彩损伤，尤其是在Light Emitting Diode(LED)得到广泛应用的博物馆光环境中。如何针对馆藏丝质文物色彩损伤进行科学评估是本研究要解决的主要问题。色差评估法是分析博物馆照明对文物色彩损伤的有效手段，但是存在相应的局限性，无法对色彩损伤的诱导期进行评估。由于文物发生色彩损伤的根本原因在于材料内部分子结构发生光化学反应，理论上说，从微观分子层面研究的拉曼光谱法能够更加科学地评估丝质文物色彩损伤。本研究将拉曼光谱引入博物馆照明领域，对比色差评估结果验证拉曼光谱色彩损伤评估的可行性和科学性。通过构成四基色LED的450, 510, 583和650 nm四种窄带光对丝质样品开展长周期照射实验，分别以CIE L*a*b*色差和拉曼光谱作为评估指标，计算得到基于两种评估方法的不同窄带光对丝质文物的色彩相对损伤系数，分别为450 nm∶510 nm∶583 nm∶650 nm=1.00∶0.63∶0.48∶0.32和450 nm∶510 nm∶583 nm∶650 nm=1.00∶0.69∶0.47∶0.27。结果一方面表明，两种方法得到的四种窄带光对丝质文物的色彩损伤趋势是一致的，即450 nm>510 nm>583 nm>650 nm，波长越短对丝质文物的色彩损伤程度越大，说明拉曼光谱是一种能够量化评估丝质文物色彩损伤的可行方法；另一方面表明，基于拉曼参数计算的色彩相对损伤系数的比例差异更大。丝质样品的老化过程中存在诱导期。色差法难以分析丝质样品诱导期的色彩变化，而拉曼光谱分析则可灵敏地检测出相应的分子结构变化，包括诱导期。因此，拉曼光谱法能够对丝质文物的色彩损伤进行更加科学地评估。同时，研究得到的构成LED光谱的四种窄带光对丝质文物色彩相对损伤系数，可以为这类光源在丝质文物照明中的损伤度评估和博物馆准入评估提供依据。

Comparison of Raman Spectroscopy and Color Difference in the Light-Induced Color Damage Evaluation of Cultural Heritages With Silk

Silk is one of the important collections in the museum, with high cultural, artistic and historical value. As a kind of unstable protein organic material, silk is extremely susceptible to the color damage such as yellowing caused by optical radiation, particularly in the museum light environment where Light Emitting Diode (LED) is widely used. How to evaluate the light-induced color damage to silk scientifically is the main problem to be solved in this study. Although effectively analyzed in the color damage of museum lighting to silk, there is limitations for the color difference evaluation method that is impossible to evaluate the color damage in the induction period. Since the fundamental cause of the color damage to silk lies in the photochemical reaction of the molecular structure inside the material, theoretically, the color damage to silk can be evaluated more scientifically based on Raman spectroscopy, which is studied at the microscopic molecular level. In this study, Raman spectroscopy was introduced into the field of museum lighting to verify its feasibility and scientificity in the color damage evaluation by comparing the evaluation results of the color difference method. Four narrow-band lights at 450, 510, 583, and 650 nm peak wavelengths that constitute the four-primary LED were used to carry out the long-period illumination experiment on silk samples. The relative color damage coefficients of four narrow-band lights on silk samples based on two evaluation methods of color difference and Raman spectroscopy were calculated, which were 450 nm∶510 nm∶583 nm∶650 nm=1.00∶0.63∶0.48∶0.32, and 450 nm∶510 nm∶583 nm∶650 nm=1.00∶0.69∶0.47∶0.27, respectively. On the one hand, the results show that the color damage trend of four narrow-band lights obtained by two methods is consistent, that is, the shorter the peak wavelength, the higher the color damage to silk samples, indicating that Raman spectroscopy is a feasible method to evaluate the light-induced color damage to the silk. On the other hand, the ratio difference of the coefficient obtained based on Raman spectroscopy is greater. There is an induction period in the aging process of silk samples. It is difficult to analyze the change during the induction period by the method of color difference, while the change of molecular structure, including in the induction period, can be detected sensitively by Raman spectroscopy to evaluate the light-induced color damage to silk samples more scientifically. At the same time, the relative color damage coefficients provide a basis for the light-induced color damage evaluation and museum admission evaluation of the four-primary light-emitting diode in the illumination of silk.