Department of Physical and Analytical Chemistry, Universidad de Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain.
Department of Physical and Analytical Chemistry, Universidad de Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain.
Spectrochim Acta A Mol Biomol Spectrosc. 2021 May 15;253:119568. doi: 10.1016/j.saa.2021.119568. Epub 2021 Feb 9.
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.
我们探讨了红外高光谱微观成像在研究人工紫外线老化后绘画层中有机粘合剂变化的潜力。考虑到三种不同的粘合剂，即兔皮胶（基于胶原蛋白的蛋白质粘合剂）、亚麻籽油（代表干性油）和蛋彩画（蛋黄和亚麻籽油的混合物），我们制备了一组油漆模拟件。为了研究颜料-粘合剂相互作用的影响，我们考虑了四种颜料（朱砂、雌黄、蓝铜矿和铅白），并通过光纤反射光谱（FORS）观察颜色变化。FTIR 微观图像提供了绘画复杂和不均匀结构的代表性图片，因为每个像素都包含了从它记录的样品区域的整个光谱。主成分分析（PCA）用于分析 FTIR 图像数据，以提取在紫外线诱导老化过程中发生的光谱变化的有用信息。在这项针对模型样品的初步研究中，主要观察到取决于粘合剂及其由于紫外线暴露而降解的趋势。在兔皮胶的情况下，已经检测到一些过程，例如蛋白质的氧化形成羰基基团和酰胺带位置的变化。单独的亚麻籽油蒸发，可能是由于三酰基甘油的分解，在单独使用粘合剂时没有注意到，但在与颜料混合使用时则没有注意到。在这些情况下，在加载图中观察到了其他取决于颜料的光谱特征，即在羰基带的变宽、羧酸和二羧酸的出现以及金属羧酸盐的形成。对于蛋彩画，检测到的主要变化与蛋黄部分存在的脂质成分的氧化有关。此外，在这种情况下，得分图中观察到的趋势表明，铅白的存在加速了其氧化。有趣的是，当使用这种粘合剂时，彩色颜料的主要稳定性。
