This study explores the natural alteration of verdigris, both in the form of neutral verdigris (Cu(II) (CH 3 COO) 2 ⋅H 2 O) and basic verdigris (Cu(II) x (CH 3 COO) y (OH) z ⋅ n H 2 O), through combined Raman spectroscopy and X-ray diffraction investigation of samples created seven to eleven years prior to analysis. The naturally aged paint films of neutral or basic verdigris in gum arabic on paper and parchment provide insight into the pigment’s well-known instability relevant to historical works in aqueous media on maps, prints, books and manuscript materials. The latter historical application is an area that has received far less attention than alteration of verdigris in oil-based paint films. Findings shed new light on alternate pathways for conversion of neutral verdigris to basic verdigris, including the formation of a previously unknown form of verdigris and amorphous material on alkaline paper substrates. Additionally, we demonstrate for the first time that copper hydroxyl chlorides can form in situ from neutral verdigris, in this case on parchment that has a chlorine-rich surface. These results advance our understanding of neutral verdigris alteration, and complement results from our prior artificial ageing study. Both studies point to neutral verdigris as the historically more important form throughout its heyday. Improved understanding of neutral verdigris instability and its alteration pathways are critical for confident identification of the pigment in historical works, leading to better risk assessment of collections of verdigris-containing heritage, such as maps.

中文翻译：

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通过拉曼光谱和X射线衍射追踪铜绿颜料的变化，第二部分：自然老化

这项研究探索了天然铜绿的变化，包括中性铜绿（Cu（II）（CH 3 COO）2⋅H2 O）和碱性铜绿（Cu（II）x（CH 3 COO）y（OH）的形式z⋅n H 2 O），通过组合拉曼光谱法和X射线衍射研究分析前7至11年生成的样品。在纸和羊皮纸上使用阿拉伯树胶制成的自然老化的中性或碱性铜绿漆膜，可深入了解该颜料与地图，印刷品，书籍和手稿材料中水介质中的历史作品有关的众所周知的不稳定性。后者的历史应用领域比油基漆膜中的铜绿的改变受到的关注要少得多。研究结果为将中性鲜绿转化为基本鲜绿提供了新的思路，包括在碱性纸基材上形成以前未知形式的铜绿和无定形材料。此外，我们首次证明了中性铜绿可以原位形成羟基铜氯化物，在这种情况下是在羊皮纸上富含氯的表面。这些结果提高了我们对中性铜绿变化的理解，并补充了我们先前人工老化研究的结果。两项研究均指出，中性铜绿是整个鼎盛时期中历史上更重要的形式。更好地理解中性铜绿不稳定性及其变化途径对于可靠地鉴定历史作品中的色素至关重要，从而可以更好地评估含铜绿的遗产（例如地图）的风险。