Effects of Illumination on Paper and Silk Substrates of Traditional Chinese Painting and Calligraphy Measured with Raman Spectroscopy

As the substrates of traditional Chinese painting and calligraphy, paper and silk are susceptible to optical radiation in museum illumination, resulting in mechanical damage, the origins of which are changes in microscopic molecular structure. However, there is no effective method of quantitatively evaluating the microscopic molecular structural changes caused by irradiation. In this study, Raman spectroscopy was introduced for illumination research on the paper and silk substrates in museums. Four narrow-emitting light sources with different peak wavelengths, red (650 nm), amber (583 nm), green (510 nm), and blue (450 nm), which together constitute the spectrum of a white light emitting diode (LED), were used as experimental light sources. As experimental specimens, paper and silk substrates were irradiated by the four light sources. The Raman spectra of the specimens were collected before and after the illumination. By analyzing the variations in characteristic Raman peak intensities, the relative damage coefficients of the four light sources on microscopic molecular structures in the specimens were studied. Then, we were able to design the white LED spectral irradiance distribution of the two substrates according to the corresponding damage coefficients. In conclusion, a research method for studying the microscopic molecular structural changes in the substrates of traditional Chinese painting and calligraphy based on Raman spectroscopy has been proposed, finding a solution to the long-standing challenge of how to quantitatively evaluate illumination-induced mechanical damage of substrates. These results are instructive for designing the spectral ratios of white LEDs suitable for illumination of traditional Chinese painting and calligraphy in museums.