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首页> 外文期刊>Analytical chemistry >Combined use of Synchrotron Radiation Based Micro-X-ray Fluorescence, Micro-X-ray Diffraction, Micro-X-ray Absorption Near-Edge, and Micro-Fourier Transform Infrared Spectroscopies for Revealing an Alternative Degradation Pathway of the Pigment Cadmium Y ellow in a Painting by Van Gogh
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Combined use of Synchrotron Radiation Based Micro-X-ray Fluorescence, Micro-X-ray Diffraction, Micro-X-ray Absorption Near-Edge, and Micro-Fourier Transform Infrared Spectroscopies for Revealing an Alternative Degradation Pathway of the Pigment Cadmium Y ellow in a Painting by Van Gogh

机译：结合使用基于同步辐射的微X射线荧光，微X射线衍射，微X射线吸收近边缘和微傅里叶变换红外光谱技术，揭示了Y族中C色素Y的另一种降解途径梵高的一幅画

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Over the past years a number of studies have described the instability of the pigment cadmium yellow (CdS). In a previous paper we have shown how cadmium sulfide on paintings by James Ensor oxidizes to CdSO_4·H_2O. The degradation process gives rise to the fading of the bright yellow color and the formation of disfiguring white crystals that are present on the paint surface in approximately 50 μm sized globular agglomerations. Here, we study cadmium yellow in the painting "Flowers in a blue vase" by Vincent van Gogh. This painting differs from the Ensor case in the fact that (a) a varnish was superimposed onto the degraded paint surface and (b) the CdS paint area is entirely covered with an opaque crust. The latter obscures the yellow color completely and thus presents a seemingly more advanced state of degradation. Analysis of a cross-sectioned and a crushed sample by combining scanning microscopic X-ray diffraction (μ-XRD), microscopic X-ray absorption near-edge spectroscopy (μ-XANES), microscopic X-ray fluorescence (μ-XRF) based chemical state mapping and scanning microscopic Fourier transform infrared (μ-FT-IR) spectrometry allowed unravelling the complex alteration pathway. Although no crystalline CdSO_4 compounds were identified on the Van Gogh paint samples, we conclude that the observed degradation was initially caused by oxidation of the original CdS pigment, similar as for the previous Ensor case. However, due to the presence of an overlying varnish containing lead-based driers and oxalate ions, secondary reactions took place. In particular, it appears that upon the photoinduced oxidation of its sulfidic counterion, the Cd~(2+) ions reprecipitated at the paint/varnish interface after having formed a complex with oxalate ions that themselves are considered to be degradation products of the resin and/or oil in the varnish. The SO_4~(2-) anions, for their part, found a suitable reaction partner in Pb~(2+) ions stemming from a dissolved lead-based siccative that was added to the varnish to promote its drying. The resulting opaque anglesite compound in the varnish, in combination with the underlying CdC_2O_4 layer at the paint/varnish interface, account for the orange-gray crust that is disfiguring the painting on a macroscopic level. In this way, the results presented in this paper demonstrate how, through a judicious combined use of several microanalytical methods with speciation capabilities, many new insights can be obtained from two minute, but highly complex and heterogeneous paint samples.
机译：在过去的几年中，许多研究描述了颜料镉黄（CdS）的不稳定性。在先前的论文中，我们已经显示了詹姆斯恩索（James Ensor）绘画上的硫化镉如何被氧化为CdSO_4·H_2O。降解过程会导致亮黄色褪色，并形成漆面白色晶体，该白色晶体以约50μm大小的球状团聚形式存在于油漆表面。在这里，我们研究文森特·凡·高（Vincent van Gogh）的画作“蓝色花瓶中的花朵”中的镉黄。该涂漆与Ensor情况的不同之处在于：（a）将清漆叠加在退化的漆面上，（b）CdS漆区域完全被不透明的硬皮覆盖。后者完全掩盖了黄色，因此呈现出似乎更高级的降解状态。通过结合扫描显微X射线衍射（μ-XRD），显微X射线吸收近边缘光谱（μ-XANES），显微X射线荧光（μ-XRF）来分析横截面和压碎的样品化学状态图谱和扫描显微傅里叶变换红外光谱（μ-FT-IR）可以揭示复杂的变化途径。尽管在梵高涂料样品上未发现结晶的CdSO_4化合物，但我们得出的结论是，观察到的降解最初是由原始CdS颜料的氧化引起的，这与之前的Ensor情况类似。但是，由于上层清漆中含有铅基干燥剂和草酸根离子，因此发生了次级反应。特别地，似乎在其硫化抗衡离子的光诱导氧化后，Cd〜（2+）离子与草酸盐离子形成络合物后在涂料/清漆界面上重新沉淀，而草酸盐离子本身被认为是树脂的降解产物。 /清漆中的油。就SO_4〜（2-）阴离子而言，在溶解于铅的干燥剂中的溶解的铅基干燥剂产生的Pb〜（2+）离子中找到了合适的反应伙伴。清漆中生成的不透明角位化合物与油​​漆/清漆界面处的基础CdC_2O_4层相结合，说明了橙灰色结皮在宏观层面上破坏了涂漆。通过这种方式，本文提出的结果证明了如何通过明智地结合使用几种具有形态分析功能的微量分析方法，可以从两分钟但高度复杂且异构的涂料样品中获得许多新见解。

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