Blackening of lead white: Study of model paintings,Journal of Raman Spectroscopy

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Blackening of lead white: Study of model paintings
Journal of Raman Spectroscopy ( IF 2.4 ) Pub Date : 2020-04-04 , DOI: 10.1002/jrs.5879
Manuela Vagnini ₁ , Riccardo Vivani ₂ , Antonio Sgamellotti _{1,

3,

4} , Costanza Miliani _{1,

3}

Affiliation

This study is aimed at clarifying the causes of lead white darkening by studying the behaviour of its two components: cerussite and hydrocerussite. Their degradation processes have been investigated by micro‐Raman spectroscopy both in an alkaline environment generated from a fresco conditions and in the presence of NaClO as an external oxidizing agent. It was confirmed that no darkening of mural paintings components occurs in the alkaline environment, highlighting that any blackening process must be due to an external agent. On the contrary, a markedly different behaviour was observed for cerussite and hydrocerussite in the alkaline conditions generated by a fresco technique, where formation of different partially oxidized products was observed. Furthermore, the conditions required for blackening of cerussite and hydrocerussite with NaClO were in‐depth investigated by X‐ray diffraction analyses, finding that the reaction products consist of lead (IV) in plattnerite and scrutinyite forms, produced in different amounts. Hydrocerussite turned out to be the more reactive component, giving rise mainly to the more kinetically favoured scrutinyite, whereas, in the case of cerussite, plattnerite was prevalently formed owing to its larger thermodynamical stability.

中文翻译：

铅白发黑：模型绘画的研究

这项研究旨在通过研究其铅锌矿和水铅硅石两个成分的行为来弄清铅白变黑的原因。在壁画条件下产生的碱性环境中以及在作为外部氧化剂的NaClO存在下，通过显微拉曼光谱研究了它们的降解过程。已确认在碱性环境中不会使壁画成分发暗，这表明任何发黑过程都必须归因于外部因素。相反，在壁画产生的碱性条件下，观察到的陶粒和水陶粒的行为明显不同。技术，观察到形成不同的部分氧化产物。此外，通过X射线衍射分析深入研究了用NaClO氧化铜铁矿和水铜铁矿所需的条件，发现反应产物由铅锌矿和辉锰矿形式的铅（IV）组成，并以不同的量产生。结果表明，水铜矿是反应性更高的组分，主要是由动力学上更有利的水铝锰矿引起，而在铜矿的情况下，由于其更大的热力学稳定性，白铁矿普遍形成。

更新日期：2020-04-04

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