We explored the potential of infrared hyperspectral microimages to investigate the alteration of organic binders in pictorial layers after artificial UV light ageing. A set of paint mockups was prepared considering three different binders, namely, rabbit glue (a collagen-based proteinaceous binder), linseed oil (representative of drying oils) and egg tempera (a mixture of egg yolk and linseed oil). Four pigments (vermilion, orpiment, azurite and lead white) were considered in order to investigate the influence of pigment-binder interaction, following color changes by means of fiber optic reflectance spectroscopy (FORS). FTIR micro-images provided a representative picture of the complex and heterogeneous structure of paintings since each pixel contained the whole spectrum of the sample area from it was recorded. Principal component analysis (PCA) was used to analyze the FTIR images data in order to extract useful information about spectral changes taking place during UV induced ageing.

Significant trends were observed, mainly depending on the binders and their degradation as a consequence of UV exposition in this pilot study on model samples. Several processes, such as the oxidation of proteins with the formation of carbonyl moieties and changes in amide band positions have been detected in the case of rabbit skin glue. The evaporation of linseed oil, probably due to the breakdown of the triacylglycerols, has been noticed for the binder alone but not when it was mixed with the pigments. In these cases, other spectral features depending on the pigment have been observed in the loading plots upon oxidation, namely the broadening of the carbonyl band, the appearance of carboxylic and dicarboxylic acids and the formation of metal carboxylates. For egg tempera, the main changes detected were related to the oxidation of lipidic components present in egg yolk fraction. Furthermore, in this case, the trend observed in the score graphs suggested that the presence of lead white accelerates its oxidation. It is interesting to note the major stability of the colored pigments when using this binder.

我们探索了红外高光谱显微图像的潜力，以研究人工紫外光老化后图像层中有机粘合剂的变化。考虑到三种不同的粘合剂，制备了一套油漆样机，即兔子胶（一种基于胶原蛋白的粘合剂），亚麻子油（代表干性油）和蛋彩画（蛋黄和亚麻子油的混合物）。为了研究颜料-粘合剂相互作用的影响，并通过光纤反射光谱法（FORS）观察了颜色变化，考虑了四种颜料（朱红色，雌黄，蓝绿色和铅白）。FTIR显微图像提供了绘画复杂而异质结构的代表性图像，因为每个像素都包含了整个样品区域的光谱。

在该模型样品的初步研究中，观察到了显着的趋势，主要取决于粘合剂及其因紫外线暴露而导致的降解。在兔皮胶的情况下，已经检测到多种过程，例如蛋白质氧化与羰基部分的形成以及酰胺带位置的变化。亚麻籽油的蒸发可能是由于三酰基甘油的分解所致，仅在粘合剂中发现了挥发，而在与颜料混合时却没有发现。在这些情况下，在氧化后的负载图中已观察到取决于颜料的其他光谱特征，即羰基带的加宽，羧酸和二羧酸的出现以及金属羧酸盐的形成。对于蛋蛋彩画 检测到的主要变化与蛋黄级分中脂质成分的氧化有关。此外，在这种情况下，在分数图中观察到的趋势表明，铅白的存在会加速其氧化。有趣的是，使用这种粘合剂时，有色颜料的主要稳定性。