CNR-ISTM, Istituto di Science e Tecnologie Molecolari , Perugia, Italy.
Department of Chemical Engineering, Imperial College London , South Kensington Campus, London, United Kingdom.
Anal Chem. 2017 Jan 17;89(2):1283-1289. doi: 10.1021/acs.analchem.6b04065. Epub 2016 Dec 28.
Protrusions, efflorescence, delamination, and opacity decreasing are severe degradation phenomena affecting oil paints with zinc oxide, one of the most common white pigments of the 20th century. Responsible for these dramatic alterations are the Zn carboxylates (also known as Zn soaps) originated by the interaction of the pigment and the fatty acids resulting from the hydrolysis of glycerides in the oil binding medium. Despite their widespread occurrence in paintings and the growing interest of the scientific community, the process of formation and evolution of Zn soaps is not yet fully understood. In this study micro-attenuated total reflection (ATR)-FT-IR spectroscopic imaging was required for the investigation at the microscale level of the nature and distribution of Zn soaps in the painting Alchemy by J. Pollock (1947, Peggy Guggenheim Collection, Venice) and for comparison with artificially aged model samples. For both actual samples and models, the role of AlSt(OH), a jellifying agent commonly added in 20th century paint tube formulations, proved decisive for the formation of zinc stearate-like (ZnSt) soaps. It was observed that ZnSt-like soaps first form around the added AlSt(OH) particles and then eventually grow within the whole painting stratigraphy as irregularly shaped particles. In some of the Alchemy samples, and diversely from the models, a peculiar distribution of ZnSt aggregates arranged as rounded and larger particles was also documented. Notably, in one of these samples, larger agglomerates of ZnSt expanding toward the support of the painting were observed and interpreted as the early stage of the formation of internal protrusions. Micro-ATR-FT-IR spectroscopic imaging, thanks to a very high chemical specificity combined with high spatial resolution, was proved to give valuable information for assessing the conservation state of irreplaceable 20th century oil paintings, revealing the chemical distribution of Zn soaps within the paint stratigraphy before their effect becomes disruptive.
突起、发花、分层和不透明性降低是影响含氧化锌的油画的严重降解现象，氧化锌是 20 世纪最常见的白色颜料之一。导致这些剧烈变化的是 Zn 羧酸盐（也称为 Zn 皂），它是由颜料与油结合介质中甘油酯水解产生的脂肪酸相互作用形成的。尽管 Zn 皂在绘画中广泛存在，并且科学界越来越感兴趣，但它们的形成和演化过程尚未完全了解。在这项研究中，需要使用微衰减全反射（ATR）-FT-IR 光谱成像技术，在微观尺度上研究 J. Pollock 的画作《炼金术》（1947 年，佩吉·古根海姆收藏，威尼斯）中 Zn 皂的性质和分布，并与人工老化的模型样品进行比较。对于实际样品和模型，AlSt(OH)（一种常用于 20 世纪颜料管配方中的胶凝剂）的作用被证明对硬脂酸锌（ZnSt）样皂的形成具有决定性作用。观察到 ZnSt 样皂首先在添加的 AlSt(OH)颗粒周围形成，然后最终作为不规则形状的颗粒在整个绘画层中生长。在《炼金术》的一些样本中，与模型不同，还记录到 ZnSt 聚集物呈圆形和较大颗粒的特殊分布。值得注意的是，在其中一个样本中，观察到向画作支撑物扩展的较大 ZnSt 团聚体，并将其解释为内部突起形成的早期阶段。微 ATR-FT-IR 光谱成像由于具有非常高的化学特异性和高空间分辨率，被证明可以为评估不可替代的 20 世纪油画的保护状态提供有价值的信息，揭示 Zn 皂在其产生破坏性影响之前在绘画层中的化学分布。
