Blue colors were sparsely used in the first colored Japanese ukiyo‐e prints but became predominant during the 19th century, mainly due to the integration of the synthetic Prussian blue in the palette of the printers around 1830. For a long time, researchers have assumed that the traditional Japanese organic blue colorants such as indigo were substituted by cheaper Prussian blue. Some analytical studies conducted on such artworks showed evidence of the common use of indigo and Prussian blue in Japanese paintings, alone or mixed together. Recent measurements carried out on bluish areas of an ukiyo‐e designed by Utamaro showed the simultaneous use of the two pigments. However, if visible reflectance spectroscopy suggested the single use of Indigo, Fourier transform infrared spectroscopy (FTIR) also indicated the presence of Prussian blue. These results question about the possible identification of all the pigments of a colored mixture by using a single analytical technique. Without using FTIR spectroscopy, the Prussian blue would not have been detected, whereas on infrared spectra the expected specific bands ascribed to indigo are not identified. The objective of this work is to investigate mixtures of pigments, using noninvasive spectroscopic techniques in order to assess their limits of detection. Fluorimetry, hyperspectral imaging, and infrared spectroscopies have been performed on three color charts made of indigo, Prussian blue, and mixtures of them at different proportions of matter. The results emphasize the systematic identification of Prussian blue thanks to infrared spectroscopy, whereas the identification of indigo, mixed with Prussian blue, appears to be more challenging.

中文翻译：

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蓝色可以掩盖另一个！靛蓝和普鲁士蓝混合物的无创多光谱分析

在日本的第一幅彩色浮世绘中很少使用蓝色，但在19世纪时占主导地位，这主要是由于1830年左右，合成普鲁士蓝已整合到打印机的调色板中。长期以来，研究人员一直认为传统的日本有机蓝色染料（如靛蓝）被便宜的普鲁士蓝代替。对此类艺术品进行的一些分析研究表明，单独或混合使用靛蓝和普鲁士蓝在日本绘画中很常见。最近对浮世绘的蓝色区域进行的测量由Utamaro设计的产品显示了两种颜料的同时使用。但是，如果可见反射光谱法建议使用靛蓝，则傅立叶变换红外光谱法（FTIR）也表明存在普鲁士蓝。这些结果对使用单一分析技术可能识别出有色混合物中所有颜料的问题提出了质疑。如果不使用FTIR光谱，则不会检测到普鲁士蓝，而在红外光谱上，未识别出归因于靛蓝的预期特定谱带。这项工作的目的是使用无创光谱技术研究颜料混合物，以评估其检测极限。荧光法，高光谱成像和红外光谱已在由靛蓝，普鲁士蓝，以及它们在不同比例的物质中的混合。结果强调了借助红外光谱对普鲁士蓝的系统鉴定，而靛蓝与普鲁士蓝的混合鉴定似乎更具挑战性。