Hradil David, Čermáková Zdeňka, Hradilová Janka, Bezdička Petr, Míková Jitka
Institute of Inorganic Chemistry of the Czech Academy of Sciences, v.v.i., ALMA Laboratory, Řež, Czech Republic.
Academy of Fine Arts in Prague, ALMA Laboratory, Prague, Czech Republic.
Appl Spectrosc. 2024 Nov;78(11):1136-1153. doi: 10.1177/00037028241280989. Epub 2024 Sep 28.
Azurite, a historical blue mineral pigment, has previously been described to contain certain elemental impurities. These may originate from host rocks, vein fillings, or the primary copper ore mineralization. In this study, azurites (and also green malachites) from three important Central European deposits with a potential of being exploited for pigment usage already in the Middle Ages have been studied, together with azurite from Chessy, France, with a different geological setting. Using electron probe microanalysis and, more importantly, laser ablation inductively coupled plasma mass spectroscopy for trace elemental analysis, several indicators were pinpointed as important for provenance: characteristic elemental fingerprint of the deposit, e.g., elevated lead (Pb) in combination with rare earth elements, may be combined with zinc (Zn)/arsenic (As) ratio (indicating sources of excess Zn in the primary deposit) and the overall amount of metal impurities (suggesting the source mineral of copper for azurite formation). In addition, malachites from the same deposits were found to preferentially incorporate primary ore metal elements as well as Cd, Mg, Mn, or U. Therefore, if azurite pigment contains an elevated amount of malachite as an impurity, it may significantly influence the overall elemental composition. The results obtained on geological samples were applied to two micro-samples of works of art containing azurite-rich layers originating from the 13th-14th and 16th centuries. It was shown that it is highly beneficial to focus on the overall trace elemental composition of the paint layer and not on the admixed mineral grains, as their presence, especially in minute micro-samples, is largely accidental and thus not representative. Although a higher number of samples need to be studied in the future, the newly described criteria made it possible to exclude some of the localities of the employed azurite pigment. This confirmed the key importance of trace elements analysis of mineral pigments for the provenance studies of fine arts.
蓝铜矿是一种历史悠久的蓝色矿物颜料，此前有描述称其含有某些元素杂质。这些杂质可能源自围岩、脉石充填物或原生铜矿石矿化。在本研究中，对来自中欧三个重要矿床的蓝铜矿（以及绿色孔雀石）进行了研究，这些矿床在中世纪就有被开采用于颜料的潜力，同时还研究了来自法国谢西、地质背景不同的蓝铜矿。通过电子探针微分析，更重要的是利用激光烧蚀电感耦合等离子体质谱法进行微量元素分析，确定了几个对产地溯源很重要的指标：矿床的特征元素指纹，例如铅（Pb）与稀土元素含量升高，可与锌（Zn）/砷（As）比值（表明原生矿床中过量锌的来源）以及金属杂质总量（暗示蓝铜矿形成时铜的来源矿物）相结合。此外，发现同一矿床的孔雀石优先吸收原生矿石中的金属元素以及镉、镁、锰或铀。因此，如果蓝铜矿颜料含有大量作为杂质的孔雀石，可能会显著影响其整体元素组成。将在地质样品上获得的结果应用于两件艺术品的微样品，这两件艺术品含有源自13至14世纪和16世纪的富含蓝铜矿的层。结果表明，关注颜料层的整体微量元素组成而非混合的矿物颗粒非常有益，因为它们的存在，尤其是在微小的微样品中，很大程度上是偶然的，因此不具有代表性。尽管未来需要研究更多的样品，但新描述的标准使得有可能排除一些所用蓝铜矿颜料的产地。这证实了矿物颜料微量元素分析对美术作品产地溯源研究的关键重要性。
