Chen-Wiegart Yu-Chen Karen, Catalano Jaclyn, Williams Garth J, Murphy Anna, Yao Yao, Zumbulyadis Nicholas, Centeno Silvia A, Dybowski Cecil, Thieme Juergen
Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York, USA.
National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York, USA.
Sci Rep. 2017 Sep 14;7(1):11656. doi: 10.1038/s41598-017-11525-1.
The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution, showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.
从15世纪至今的数百幅油画中，铅、锌和铜羧酸盐（皂类）的形成已导致明显的损坏。通过尚未明了的传输现象，油基介质中的游离脂肪酸穿过颜料层，与含重金属的颜料发生反应，形成皂类。为了研究元素偏析、所形成化合物的类型以及可能的反应机制之间的复杂关联，利用同步辐射X射线技术对一幅15世纪油画的颜料样本横截面进行了检测。采用元素相关密度分布进行定量分析的X射线荧光（XRF）显微镜显示，在受皂类影响的区域存在铅和锡的偏析。铅L3吸收边附近的X射线吸收近边结构（XANES）表明，可以区分铅颜料和铅皂，而微XANES则提供了有关漆膜化学不均匀性的更多信息。本文讨论了这些基于同步辐射的技术的优缺点，并与常规用于分析颜料样本的方法进行了比较。所呈现的结果为改进从艺术品中提取的样本信息以及将模型颜料样本中的观察结果与自然老化样本中的观察结果相关联奠定了基础，以便深入了解皂类形成的机制。
