Visualization of As(III) and As(V) distributions in degraded paint micro-samples from Baroque-and Rococo-era paintings (original) (raw)
Related papers
J. Anal. At. Spectrom., 2015
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 (m-XRF) reveals arsenic to be distributed throughout the whole multi-layered paint system. Arsenic (As) K-edge micro-X-ray absorption near edge structure (m-XANES) analyses indicate the presence of an intact As x S y pigment, arsenite compounds (As 3+ ; As 2 O 3 ), and arsenate compounds (As 5+ ); the latter are certainly present as calcium, lead, aluminium and iron arsenates. Sulfur (S) K-edge m-XANES points to the conversion of the sulfide (S 2À ) group to a sulfate (SO 4 2À ) group, probably via an elemental sulfur (S 0 ) or sulfoxide (S 2+ ) compound. Principal Component Analysis (PCA) and subsequent k-means clustering of multi-energy SR m-XRF maps and m-XANES were performed to identify the various arsenic species and visualize their distribution. The arsenates (As 5+ ) are spread throughout the entire paint system and dominate the photo-degraded paint and ground layers, while the arsenite compounds (As 3+ ) 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 As 5+ 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
Faculty of Science, University of Amsterdam E-mail: k.keune@rijksmuseum.nl Scientic Research and Analysis Laborator Museum, Winterthur, Delaware, USA Inorganic Chemistry and Catalysis, Debye In University, Universiteitsweg 99, 3584 CG Ut Royal Picture Gallery Mauritshuis, The Ha University of Delaware, Department of Che University of Delaware, Department of Ma Delaware, USA European Synchrotron Radiation Facility, 71 Laboratoire d'archéologie moléculaire et s 75005, Paris, France Stanford Synchrotron Radiation Lightsourc 2575 Sand Hill Rd., Menlo Park, California † Electronic supplementary informa 10.1039/c4ja00424h Cite this: J. Anal. At. Spectrom., 2015, 30, 813
2010
Sublimed (dry process) arsenic sulphide pigments have been of interest since historic and modern samples of yellow, orange or red powders and cakes containing arsenic oxide (As 2 O 3), arsenic sulphide glass (g-As x S x), members of the β-As 4 S 4-As 8 S 9 series, the χ-phase and pararealgar (As 4 S 4) were identified. The X-ray amorphous components occur as irregular masses or spherules, whereas the crystalline components consist of octahedral or tabular crystals or radially grown spherules of up to 30 μm in diameter. Artificial arsenic sulphides produced by sublimation have been found in the paint layers of a sixteenth/seventeenth-century South German polychrome recumbent sculpture in Altomünster and in Domenico Tintoretto's painting Entry of Philip II into Mantua (1579/80), which is part of the famous 'Gonzaga Cycle' (Alte Pinakothek, Munich). The identification required the use of light microscopy, X-ray diffraction and scanning electron microscopy as well as Raman analysis. Raman microspectroscopy proved to be a valuable tool, particularly for differentiation between realgar (As 4 S 4), pararealgar, and members of the β-As 4 S 4-As 8 S 9 series, which includes the χ-phase of almost identical chemical composition, as well as the distinction of X-ray amorphous arsenic sulphide glasses. If pure pararealgar is detected using Raman it is not possible to determine whether it was formed from degradation of natural realgar or from members of the β-As 4 S 4-As 8 S 9 series. Keeping in mind the close relationship between natural realgar, alacranite (As 8 S 9), β-As 4 S 4 and the χ-phase, it is highly likely that many of the arsenic sulphides found on works of art will turn out to be of artificial origin.
Heritage Science
The spontaneous chemical alteration of artists' pigment materials may be caused by several degradation processes. Some of these are well known while others are still in need of more detailed investigation and documentation. These changes often become apparent as color modifications, either caused by a change in the oxidation state in the original material or the formation of degradation products or salts, via simple or more complex, multistep reactions. Arsenic-based pigments such as orpiment (As 2 S 3) or realgar (α-As 4 S 4) are prone to such alterations and are often described as easily oxidizing upon exposure to light. Macroscopic X-ray powder diffraction (MA-XRPD) imaging on a sub area of a still life painting by the 17th century Dutch painter Martinus Nellius was employed in combination with microscopic (μ-) XRPD imaging of a paint cross section taken in the area imaged by MA-XRPD. In this way, the in situ formation of secondary metal arsenate and sulfate species and their migration through the paint layer stack they originate from could be visualized. In the areas originally painted with orpiment, it could be shown that several secondary minerals such as schultenite (PbHAsO 4), mimetite (Pb 5 (AsO 4) 3 Cl), palmierite (K 2 Pb(SO 4) 2) and syngenite (K 2 Ca(SO 4) 2 •H 2 O) have formed. Closer inspection of the cross-sectioned paint layer stack with μ-XRPD illustrates that the arsenate minerals schultenite and mimetite have precipitated at the interface between the orpiment layer and the layer below that is rich in lead white, i.e. close to the depth of formation of the arsenate ions. The sulfate palmierite has mostly precipitated at the surface and upper layers of the painting.
Analytical Chemistry, 2012
Over the past years a number of studies have described the instability of the pigment cadmium yellow (CdS). In a previous paper we have shown how cadmium sulfide on paintings by James Ensor oxidizes to CdSO 4 ·H 2 O. The degradation process gives rise to the fading of the bright yellow color and the formation of disfiguring white crystals that are present on the paint surface in approximately 50 μm sized globular agglomerations. Here, we study cadmium yellow in the painting "Flowers in a blue vase" by Vincent van Gogh. This painting differs from the Ensor case in the fact that (a) a varnish was superimposed onto the degraded paint surface and (b) the CdS paint area is entirely covered with an opaque crust. The latter obscures the yellow color completely and thus presents a seemingly more advanced state of degradation. Analysis of a cross-sectioned and a crushed sample by combining scanning microscopic X-ray diffraction (μ-XRD), microscopic X-ray absorption near-edge spectroscopy (μ-XANES), microscopic X-ray fluorescence (μ-XRF) based chemical state mapping and scanning microscopic Fourier transform infrared (μ-FT-IR) spectrometry allowed unravelling the complex alteration pathway. Although no crystalline CdSO 4 compounds were identified on the Van Gogh paint samples, we conclude that the observed degradation was initially caused by oxidation of the original CdS pigment, similar as for the previous Ensor case. However, due to the presence of an overlying varnish containing lead-based driers and oxalate ions, secondary reactions took place. In particular, it appears that upon the photoinduced oxidation of its sulfidic counterion, the Cd 2+ ions reprecipitated at the paint/varnish interface after having formed a complex with oxalate ions that themselves are considered to be degradation products of the resin and/or oil in the varnish. The SO 4 2− anions, for their part, found a suitable reaction partner in Pb 2+ ions stemming from a dissolved lead-based siccative that was added to the varnish to promote its drying. The resulting opaque anglesite compound in the varnish, in combination with the underlying CdC 2 O 4 layer at the paint/varnish interface, account for the orange-gray crust that is disfiguring the painting on a macroscopic level. In this way, the results presented in this paper demonstrate how, through a judicious combined use of several microanalytical methods with speciation capabilities, many new insights can be obtained from two minute, but highly complex and heterogeneous paint samples.
Microchemical Journal, 2018
In this paper, we used the semiconducting and lightfastness properties of arsenic sulfide pigments to study their stability by means of electrochemical and microfadometric techniques. A combination of these techniques show that in the early stage of the degradation process, amorphous arsenic sulfides are more stable than both crystalline forms, while upon longer exposure time, amorphous pigments will fade more than both natural pigments, making it less suitable. While the stability study was carried out on unbound pigments, the influence of the organic binder on the relative degradation of the arsenic sulfide pigments was investigated through a multi-analytical approach on pigment/binder mock-up paint samples. For this purpose, the formation of arsenic trioxide was assessed by micro Fourier transform infrared (µ-FTIR) spectroscopy while the influence of the binder on the formation of sulfates was studied by means of synchrotron radiation X-ray near edge structure (µ-XANES). Both techniques elucidate a higher stability of all pigments in gum arabic while the use of egg yolk as binder leads to the most degradation, most likely due to its sulfur-rich composition. In the context of the degradation of arsenic sulfide pigments, other binders such as animal glue, egg white or linseed oil show an intermediate impact.
2009
Two oil paintings in the collection of the Department of Prints and Drawings at the British Museum are catalogued as mechanical paintings on canvas by Francis Eginton after Philip James de Loutherbourg. While the name of de Loutherbourg is familiar, that of Eginton is less so. In the period between 1776 and 1782, Eginton, a glass painter and printmaker, participated in a shortlived partnership with Matthew Boulton, the entrepreneurial owner of the Soho Manufactory in Birmingham, to sell mechanical copies of paintings by prominent late eighteenth century artists, including,
In this study, a combination of elemental analytical techniques (MA-XRF and SEM-EDX) were used to localize arsenic sulfide pigments within a 17 th-century Dutch painting and in the stratigraphy of an 18 th-century Flemish polychrome sculpture. Once located, Raman spectroscopy was used to obtain the vibrational signature of the arsenic sulfide pigments employed. By means of the latter analytical technique and due to the very distinctive Raman scattering signal of the various arsenic sulfide compounds, it was possible to identify the arsenic-based pigments as natural orpiment and amorphous arsenic sulfide. In the latter case, based on the minor bands observed and the good condition of the paint layers, it was possible to identify pararealgar, the orangey-yellow to yellow degradation product of realgar, as the initial arsenic sulfide material used for the synthesis of the amorphous pigment. To the best of our knowledge, this is the first time that combined pararealgar/amorphous arsenic sulfide Raman spectra are reported in historical samples. Therefore, this would be the first identification of pararealgar as the starting material to produce amorphous arsenic sulfide pigments used in artworks.
Pigments-Arsenic-based yellows and reds
Open Access - Archaeological and Anthropological Sciences, 2022
This review offers an update on arsenic-bearing minerals and pigments with the aim of serving as a guide for the study of Cultural Heritage materials in which these materials can be found. The different As-bearing mineral phases (realgar, pararealgar, orpiment, anorpiment, alacranite, dimorphite, bonazziite, uzonite, wakabayashilite, duranusite, arsenolite and claudetite) and some of their light-induced products are examined. The occurrence of As-sulfides and their trade, use, alteration and degradation are also reviewed. Finally, the analytical techniques commonly used for the identification of arsenic-containing pigments are discussed. The manuscript concludes with a good practice guide and a summary of key concepts for use by those working in the field of cultural heritage. This article is part of the Topical Collection on Mortars, plasters and pigments: Research questions and answers
Analytical chemistry, 2011
The darkening of the original yellow areas painted with the chrome yellow pigment (PbCrO 4 , PbCrO 4 3 xPbSO 4 , or PbCrO 4 3 xPbO) is a phenomenon widely observed on several paintings by Vincent van Gogh, such as the famous different versions of Sunflowers. During our previous investigations on artificially aged model samples of lead chromate, we established for the first time that darkening of chrome yellow is caused by reduction of PbCrO 4 to Cr 2 O 3 3 2H 2 O (viridian green), likely accompanied by the presence of another Cr(III) compound, such as either Cr 2 (SO 4 ) 3 3 H 2 O or (CH 3 CO 2 ) 7 Cr 3 (OH) 2 [chromium(III) acetate hydroxide]. In the second part of this work, in order to demonstrate that this reduction phenomenon effectively takes place in real paintings, we study original paint samples from two paintings of V. van Gogh. As with the model samples, in view of the thin superficial alteration layers that are present, high lateral resolution spectroscopic methods that make use of synchrotron radiation (SR), such as microscopic X-ray absorption near edge (μ-XANES) and X-ray fluorescence spectrometry (μ-XRF) were employed. Additionally, μ-Raman and mid-FTIR analyses were carried out to completely characterize the samples. On both paint microsamples, the local presence of reduced Cr was demonstrated by means of μ-XANES point measurements. The presence of Cr(III) was revealed in specific areas, in some cases correlated to the presence of Ba(sulfate) and/or to that of aluminum silicate compounds.