Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi 13, 56124, Pisa, IT, Italy.
Department of Biology, University of Copenhagen, Øster Farimagsgade 5, 1353, Copenhagen, DK, Denmark.
Sci Rep. 2019 Apr 2;9(1):5533. doi: 10.1038/s41598-019-41893-9.
Modern oil paintings are affected by conservation issues related to the oil paint formulations and to the fact that they are often unvarnished, and in direct contact with the environment. Understanding the evolution of the molecular composition of modern oil paint during ageing, under the influence of environmental factors, is fundamental for a better knowledge of degradation phenomena and risk factors affecting modern art. We investigated for the first time the influence of relative humidity on the chemical composition of modern oil paints during curing and artificial ageing. For this purpose, modern oil paint layers naturally aged for 10 years were further artificially aged in low and high relative humidity conditions. Moreover, the influence of RH% on the curing of fresh paint layers was studied. The paints used in the experiments are from three suppliers (Old Holland, Winsor&Newton, and Talens), and contain cadmium or cadmium zinc sulfide as main pigment. The changes in the composition of extracts of paint samples were investigated by direct electrospray mass spectrometry with a quadrupole-time of flight mass analyser (ESI-Q-ToF). The obtained mass spectral data were interpreted by means of principal component analysis (PCA) operated on a data set containing the relative abundance of ions associated to significant molecules present in the extracts, and also by calculating the ratios between the signals relative to fatty acids, dicarboxylic acids and acylglycerols, related to hydrolysis and oxidation phenomena. The same paint samples were also analysed, in bulk, by pyrolysis gas chromatography mass spectrometry (Py-GC/MS), achieving chemical information on the total lipid fraction. High performance liquid chromatography (HPLC) ESI-Q-ToF was carried out for the characterisation of the profile of free fatty acids (FFA) and acylglycerols, defining the nature of the oils used in the paint formulations, and for the determination of the degree of hydrolysis. This study demonstrated that relative humidity conditions significantly influence the chemical composition of the paints. Ageing under high RH% conditions produced an increase of the formation of dicarboxylic acids compared to ageing under low RH%, for all paints, in addition to a higher degree of hydrolysis, followed by evaporation of free fatty acids.
现代油画受到与油画配方有关的保护问题以及它们通常未上光且直接与环境接触的事实的影响。了解在环境因素的影响下，现代油画在老化过程中分子组成的演变对于更好地了解影响现代艺术的降解现象和危险因素至关重要。我们首次研究了相对湿度对在固化和人工老化过程中现代油画化学组成的影响。为此，对自然老化 10 年的现代油画层进一步在低相对湿度和高相对湿度条件下进行人工老化。此外，还研究了 RH%对新鲜油漆层固化的影响。实验中使用的油漆来自三个供应商（Old Holland、Winsor&Newton 和 Talens），并含有镉或镉锌硫化物作为主要颜料。通过带有四极杆-飞行时间质谱仪（ESI-Q-ToF）的直接电喷雾质谱法研究了油漆样品提取物的组成变化。通过主成分分析（PCA）对包含与提取物中存在的重要分子的相对丰度相关的离子的数据组进行解释，并通过计算与水解和氧化现象相关的脂肪酸、二羧酸和酰基甘油的信号之间的比值，来解释获得的质谱数据。还对相同的油漆样品进行了 bulk 分析，通过热裂解气相色谱质谱法（Py-GC/MS），获得关于总脂质部分的化学信息。高效液相色谱（HPLC）ESI-Q-ToF 用于游离脂肪酸（FFA）和酰基甘油的特征描述，定义油漆配方中使用的油的性质，并用于测定水解度。这项研究表明，相对湿度条件对油漆的化学组成有显著影响。在高 RH%条件下老化会导致与在低 RH%条件下老化相比，所有油漆中二羧酸的形成增加，水解程度更高，然后游离脂肪酸蒸发。
