关键词: 丝绸文物, 乾隆色谱, 传统染色, 纺织品色彩, 色彩管理

Abstract:

Objective In order to gain more accurate and scientific understanding of the color of Qing dynasty silk cultural relics, this research attempts to analyze the color data of Qianlong palette from the perspective of chromaticity, and to provide a reference for the exhibition and digitalization of Qing dynasty silk cultural relics.

Method The Qianlong palette were measured with spectrophotometer CM700D, and then the color difference caused by the change of dye concentration and the stability of Qianlong palette were discussed. The colors of Qianlong palette were analyzed in L^*a^*b^* color space. By comparing the color gamut of Qianlong palette with that of sRGB, Adobe RGB and CMYK, the possibility of color restoration in the digitalization of silk relics in the Qing dynasty was analyzed.

Results It is found that when dye concentration increased, the lightness of all Qianlong palette colors decreased, but the change of chroma was inconsistent, where the chroma of green and purple decreased and the chroma of red increased (Tab. 2). In addition, when the dye concentration is increased uniformly, the color difference does not change uniformly. When the dye concentration changes, the green system of the Qianlong palette is greatly affected by the dye concentration, while the yellow system is less affected by the dye concentration. The average color difference between yellows dyed with different dye concentrations is less than 3 (Fig.2). Three repeated measurements of Qianlong palette within five months showed that Qianlong palette was stable within half a year under the natural conditions used for this study. In 42 colors Qianlong palette, the range of a^* is from -18 to 47, and the range of b^* is from -22 to 74, while in the extended 210 colors Qianlong palette, the range of a^* is from -18 to 47, and the range of b^* is from -23 to 78 (Fig.3). Comparing 42 colors Qianlong palette with 210 colors Qianlong palette, it was found that for the same dyeing process, changing only the dye concentration cannot broaden the maximum parameter range of a^* and b^*, but it greatly enriches the number of colors within the parameter range. In addition, it was found that there is an obvious color loss in the third quadrant of a^*b^* diagram. Converting (L^*, a^*, b^*) to (L^*, C^*, h), it can be seen that the hue of missing color is in range of 170°—240°(Fig.4), revealing the comparison results between the Qianlong color gamut and sRGB, Adobe RGB and CMYK. Most of the colors of the Qianlong palette are in these three color gamut, but some high chroma and lightness yellow colors exceed the gamut (Fig.5). The number of colors beyond Adobe RGB is small, and the number of yellow colors beyond sRGB is the largest, accounting for 38% of the yellow system.

Conclusion The yellow of Qianlong palette is less affected by the dye concentration, while the green is more affected by the dye concentration, and it would be more likely to make mistakes when dyeing green in Qing dynasty. In the silk cultural relics handed down in the Qing Dynasty, if the color recorded on the two fabrics is green, but the colors look different, it is necessary to consider not only the possibility of fading, but also the possible deviation in dyeing at that time. In addition, the Qianlong palette has an approximate range of a^*, b^* values, the color beyond this range was proven to be difficult to achieve in the Qing dynasty. Through strict color management and color, most of the silk relics of the Qing dynasty can display colors correctly in sRGB, Adobe RGB and CMYK. However, part of the high lightness and high chroma yellows of Qianlong palette are out of the gamut of sRGB, Adobe RGB and CMYK. Therefore, the color of these handed down silk relics of the Qing dynasty with yellow background may be distorted when they are displayed online, so it is suggested that these relics be displayed offline.

Key words: silk cultural relic, Qianlong palette, traditional dyeing, textile color, color management