Microanalysis of clay-based pigments in paintings by XRD techniques

Multitechnique Characterization of Pigments Used in Paintings by Léon Pallière

This study provides a microanalytical characterization of pigment fragments from the painting "Allegory to the Arts" and two portraits, "Rubens" and "Tintoretto," by Léon Pallière. The fragments were surface-analyzed using several near-surface methods to acquire information on the materials and determine the painting techniques utilized before the restoration. Scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS), Raman spectroscopy coupled to an optical microscope (Raman microprobe), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) revealed organic materials, hydrocerussite (Pb3(CO3)2(OH)2), cerussite (PbCO3), zincite (ZnO), chalcopyrite (CuFeS2), nepheline (K(Na,K)3AlSi4O16), calcite (CaCO3), brookite (TiO2), kinoshitalite (Ba3(Si2Al2)O10(OH)2), hematite (Fe2O3), barium magnesium silicate (Ba2Mg(Si2O7)), and aluminosilicates. Also identified were vermilion/cinnabar (HgS), copper phthalocyanine blue (C32H16CuN8), and mendipite (Pb3Cl2O2), in addition to the use of gold leaf in one of the artworks. SEM/EDS provided information on the chemical composition and surface morphology of the fragments, and XRD revealed crystalline raw materials (minerals or their synthetic analogs) used in the paintings. Raman microprobe was particularly useful in identifying pigments, providing a uniquely specific and sensitive means of identifying inorganic and organic compounds.

Clay Minerals in European Painting of the Mediaeval and Baroque Periods

Clay-based pigments are among the most traditional. Unlike other mineral pigments, they have never been fully replaced by synthetic analogues and are still used in painting today. Since their analysis requires a specific approach, detailed distinction of clay pigments has never been a part of routine chemical-technological research in fine arts—regardless of a great potential of clay minerals for determining regional provenance of the material. This review article maps and summarizes research on clay pigments in historical paintings that has been systematically pursued by authors since the beginning of this millennium. This rallying and interconnection of knowledge was an opportunity for a new reflection on the common aspects of these research projects, either methodological or interdisciplinary, since these findings are closely related to art-historical evaluation of artworks. It offers a comprehensive insight into the microanalysis of clay pigments with using powder X-ray micro-diffraction and complementary methods. Significant new findings come, for example, from research on the Italian Baroque. It becomes clear that cheap availability of raw material, pottery clays, could have played an important role in the change in painting technology at the turn of the 16th and 17th centuries.

Microanalytical study of luster glazed gilding and silvering from Baroque altarpieces

Lustering, a technique which involved the application of coloured translucent glazes over gilding and silvering was widely used to enrich and decorate altarpieces in the Baroque period. The decorations consist of a micrometric multilayered structure including several color glazes, metallic leaves and bole applied over a plaster ground. The collection of Baroque altarpieces, the oldest dating 1671 and the newest 1775 from the cathedral of Tortosa (Catalonia), is a perfect case of study of the materials used and the techniques employed throughout the period. Further information is obtained from the analysis of the reaction and aging compounds resulting from the interaction among the compounds present in the layers and between the different layers. A combination of sensitive analytical techniques, Synchrotron based μ-XRD and μ-IR and SEM-EDS which enabled the luster samples to undergo analysis without altering their original layered microstructure were selected. The nature of the compounds used to produce the yellow, green, red and blue glazes (pigments, pigment lakes and resins), metallic leaves and boles is presented. Relevant information from historical and conservation viewpoints about the origin and nature of the materials used, the making of the lusters and their reactivity and aging are also discussed.