Abstract
Impurities in paint layers executed with green and blue copper pigments, although relatively common, have been studied only little to date. Yet, their proper identification is a powerful tool for classification of paintings, and, potentially, for future provenance studies. In this paper, we present analyses of copper pigments layers from wall paintings situated in the vicinity of copper ore deposits (the palace in Kielce, the palace in Ciechanowice, and the parish church in Chotków) located within the contemporary borders of Poland. We compare the results with the analyses of copper minerals from three deposits, two local, and one historically important for the supply of copper in Europe, i.e., Miedzianka in the Holy Cross Mountains, Miedzianka in the Sudetes, and, as a reference, Špania Dolina in the Slovakian Low Tatra. Optical (OM) and electron microscopy (SEM-EDS), Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) have been used for a detailed investigation of the minute grains. Special attention has been devoted to antimony and nickel phases, as more unusual than the commonly described iron oxides. Analyses of minerals from the deposits helped to interpret the results obtained from the paint samples. For the first time, quantitative analyses of copper pigments’ impurities have been described.
Highlights
Copper minerals have been used as pigments in paintings almost since the beginning of art, though they were not as widespread as earth pigments [1]
We present the results of analyses of copper pigments’ impurities identified in paint samples obtained from three wall paintings situated in three different regions of Poland that are rich in copper minerals: the upper dining room polychromy in the former Cracow Bishops’ Palace in Kielce near the Miedzianka deposit in the Holy Cross Mountains dated to the end of the 17th c; the painted decoration of the piano nobile in the Ciechanowice Palace near Miedzianka in the Rudawy Janowickie— the Sudetes, dated to the second half of the 16th c with subsequent repaintings, and the polychromy of the Chotków church vault in lubuskie voivodeship close to the LegnicaGłogów copper district, dated to the 14th c
Samples of paint layers with more unusual impurities were selected for further studies, including molecular identification of the main copper pigment, and of bigger grains of impurities in the layers, by means of Raman spectroscopy. μRaman measurements were performed with a Nicolet Almega Dispersive Raman Spectrometer (XR, Thermo Fisher Scientific, Waltham, MA, USA), equipped with an Olympus confocal microscope and motorized stage
Summary
Copper minerals have been used as pigments in paintings almost since the beginning of art, though they were not as widespread as earth pigments [1]. If some of the above-mentioned pigments, such as copper chlorides (clinoatacamite [2], atacamite [12,29], paratacamite [12,14]), copper sulphates (brochantite [8,29], posnjakite [30]), and copper oxides (cuprite [15], tenorite [26,27]) were present in art objects, they were interpreted as alteration products of malachite or azurite; or evidence of use of a synthetic copper pigment [2,4,7,12], or natural admixtures [7,18,24,31] of malachite or azurite. Adamite [18], and mixite [19] have been positively identified as natural impurities of copper carbonates. Natural admixtures of copper carbonates, such as the green-blue mixite reported by Berrie et al [19], or the bluish posnjakite [24] had an influence on the final hue
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