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The Hague, Netherlands

Keune K.,University of Amsterdam | Mass J.,Scientific Research and Analysis Laboratory | Meirer F.,University Utrecht | Pottasch C.,Royal Picture Gallery Mauritshuis | And 7 more authors.
Journal of Analytical Atomic Spectrometry

Realgar and orpiment, arsenic sulfide pigments used in historic paints, degrade under the influence of light, resulting in transparent, whitish, friable and/or crumbling paints. So far, para-realgar and arsenic trioxide have been identified as the main oxidation products of arsenic sulfide pigments. This paper shows that after photo-degradation, various oxidation and migration processes take place. Synchrotron radiation (SR) micro-X-ray fluorescence (μ-XRF) reveals arsenic to be distributed throughout the whole multi-layered paint system. Arsenic (As) K-edge micro-X-ray absorption near edge structure (μ-XANES) analyses indicate the presence of an intact AsxSy pigment, arsenite compounds (As3+; As2O3), and arsenate compounds (As5+); the latter are certainly present as calcium, lead, aluminium and iron arsenates. Sulfur (S) K-edge μ-XANES points to the conversion of the sulfide (S2-) group to a sulfate (SO4 2-) group, probably via an elemental sulfur (S0) or sulfoxide (S2+) compound. Principal Component Analysis (PCA) and subsequent k-means clustering of multi-energy SR μ-XRF maps and μ-XANES were performed to identify the various arsenic species and visualize their distribution. The arsenates (As5+) are spread throughout the entire paint system and dominate the photo-degraded paint and ground layers, while the arsenite compounds (As3+) are located close to the intact arsenic sulfide pigment. The oxidation of arsenic trioxide into arsenates likely takes place in aqueous solutions. The presence of As5+ compounds in the paint systems indicates that the arsenic trioxide is dissolved by ambient water present in the paint. Arsenite and arsenate compounds are water soluble and are transported by water throughout the paint system. This knowledge is crucial for the conservation field, as this is the first time that (indirect) evidence of water transport within paintings has been given. © 2015 The Royal Society of Chemistry. Source

van Loon A.,University of Amsterdam | van Loon A.,Technical University of Delft | Genuit W.,Royal Dutch Shell | Pottasch C.,Royal Picture Gallery Mauritshuis | And 2 more authors.
Microchemical Journal

Direct temperature-resolved mass spectrometry (DTMS) is an analytical technique in which small (μg) amounts of sample are applied to a filament and introduced into the ion source of a mass spectrometer. It is a fast fingerprinting method particularly suitable for the characterization of oils, resins, waxes, and other compound classes in tiny complex samples from paintings. DTMS results reported thus far have been obtained using instruments with nominal mass resolution. Higher mass resolutions can be achieved by magnetic sector mass spectrometers only at the expense of a severe loss of sensitivity. Modern time-of-flight mass spectrometers, however, do provide both high resolution and high sensitivity simultaneously. The availability of accurate mass information adds another dimension to DTMS. The difference between the nominal and accurate mass, the mass defect, may be graphically presented in so-called 'Kendrick plots'. These can be used as fingerprints, enabling a quick overview of the main features in high-resolution mass spectra of complex mixtures. This paper combines DTMS with Kendrick mass defect analysis applied to a series of reference compounds commonly found in paintings. Finally, we also present the results of analysis of samples taken from the 17th-century painting of Saul and David by Rembrandt van Rijn (Mauritshuis, The Hague) that has been recently subjected to extensive conservation treatment. © 2015 Elsevier B.V. Source

Janssens K.,University of Antwerp | Van Der Snickt G.,University of Antwerp | Alfeld M.,University of Antwerp | Alfeld M.,University Pierre and Marie Curie | And 7 more authors.
Microchemical Journal

The painting Saul and David, considered to date from c. 1652 and previously attributed to Rembrandt van Rijn and/or his studio, is a complex work of art that has been recently subjected to intensive investigation and conservation treatment. The goal of the research was to give insight into the painting's physical construction and condition in preparation for conservation treatment. It was also anticipated that analysis would shed light on authenticity questions and Rembrandt's role in the creation of the painting. The painting depicts the Old Testament figures of King Saul and David. At left is Saul, seated, holding a spear and wiping a tear from his eye with a curtain. David kneels before him at the right playing his harp. In the past, the large sections with the life-size figures were cut apart and later reassembled. A third piece of canvas was added to replace a missing piece of canvas above the head of David. As part of the investigation into the authenticity of the curtain area, a number of paint micro samples were examined with LM and SEM-EDX. Given that the earth, smalt and lake pigments used in the painting could not be imaged with traditional imaging techniques, the entire painting was also examined with state of the art non-destructive imaging techniques. Special attention was devoted to the presence of cobalt-containing materials, specifically the blue glass pigment smalt considered characteristic for the late Rembrandt. A combination of quantitative electron microprobe analysis and macroscopic X-ray fluorescence scanning revealed that three types of cobalt-containing materials are present in the painting. The first type is a cobalt drier that was found in the overpaint used to cover up the canvas inset and the joins that were added in the 19th century. The other two Co-containing materials are part of the original paint used by Rembrandt and comprise two varieties of smalt, a K-rich glass pigment that derives its gray-blue color by doping with Co-ions. Smalt paint with a higher Ni content (NiO:CoO ratio of around 1:4) was used to depict the blue stripes in Saul's colorful turban, while smalt with a lower Ni content was employed (NiO:CoO ratio of around 1:5) for the broad expanses of Saul's garments. The presence of two types of smalt not only supports the recent re-attribution of the painting to Rembrandt, but also that the picture was painted in two phases. Saul's dark red garment is painted in a rough, "loose" manner and the now discolored smalt-rich layer was found to have been partially removed during a past restoration treatment/s. In contrast, the blue-green smalt in the turban is much better preserved and provides a colorful accent. While the use of different types of smalt in a Rembrandt painting has been previously identified using quantitative EDX analysis of paint cross-sections, to the best of our knowledge this is the first time such a distinction has been observed in a 17th-century painting using non-destructive imaging techniques. In addition to the XRF-based non-invasive elemental mapping, hyperspectral imaging in the visual to near-infrared (VNIR) region was also carried out. © 2016 Elsevier B.V. Source

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