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“Methods and materials of the Amsterdam sunflowers”. Geldof M, Monico L, Johnson DH, Miliani C, Romani A, Grazia C, Buti D, Brunetti BG, Janssens K, Van der Snickt G, Vanmeert F page 85 (2019).
Abstract: This chapter explains the materials and techniques employed in the Amsterdam Sunflowers, enabling a comparison with the London version described in chapter 3. Building upon the 2016 article published in the National Gallery Technical Bulletin, it incorporates the latest findings gained by computer-assisted methods used to characterize the canvas support, as well as in-situ campaigns of non-invasive investigation together with further analysis of microscopic paint samples. The chapter sequence follows the steps in Van Gogh's working practice. Starting with the canvas, automated analysis of the weave enables the provenance of the canvas to be traced back to a particular roll of linen ordered by Van Gogh. Combining technical evidence with knowledge of historical manufacturing techniques further allows us to reconstruct the way in which Van Gogh divided his canvas roll into pieces used for Sunflowers and other paintings. We go on to consider how, with the original painting at hand, he used charcoal to transfer the motif of the London Sunflowers onto his blank canvas. Despite careful planning of the composition, an adjustment was required late in the working process, when Van Gogh added a painted wooden strip to extend the background above the flower at the top edge of the canvas. The artist's process of working up the composition in paint is described, paying special attention to his use of colour. The pigments and pigment mixtures used in the Amsterdam Sunflowers have been comprehensively mapped and are compared with the London picture, with discussion of some similarities and differences that account for the distinctive colour scheme of each painting. This understanding of colour application in the Amsterdam Sunflowers lays the foundation for subsequent chapters that will go on to consider the impact of light-induced colour changes that have taken place over time, and the related need to define appropriate lighting guidelines for the future safe preservation of this painting and others made with similar materials (chapters 5 and 7).
Keywords: H1 Book chapter; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Cultural Heritage Sciences (ARCHES)
DOI: 10.1017/9789048550531.005
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“Deeper insights into the photoluminescence properties and (photo)chemical reactivity of cadmium red (CdS1-xSex) paints in renowned twentieth century paintings by state-of-the-art investigations at multiple length scales”. Monico L, Rosi F, Vivani R, Cartechini L, Janssens K, Gauquelin N, Chezganov D, Verbeeck J, Cotte M, D'Acapito F, Barni L, Grazia C, Buemi LP, Andral J-L, Miliani C, Romani A, The European Physical Journal Plus 137, 311 (2022). http://doi.org/10.1140/EPJP/S13360-022-02447-7
Abstract: Cadmium red is the name used for denoting a class of twentieth century artists' pigments described by the general formula CdS1-xSex. For their vibrant hues and excellent covering power, a number of renowned modern and contemporary painters, including Jackson Pollock, often used cadmium reds. As direct band gap semiconductors, CdS1-xSex compounds undergo direct radiative recombination (with emissions from the green to orange region) and radiative deactivation from intragap trapping states due to crystal defects, which give rise to two peculiar red-NIR emissions, known as deep level emissions (DLEs). The positions of the DLEs mainly depend on the Se content of CdS1-xSex; thus, photoluminescence and diffuse reflectance vis-NIR spectroscopy have been profitably used for the non-invasive identification of different cadmium red varieties in artworks over the last decade. Systematic knowledge is however currently lacking on what are the parameters related to intrinsic crystal defects of CdS1-xSex and environmental factors influencing the spectral properties of DLEs as well as on the overall (photo)chemical reactivity of cadmium reds in paint matrixes. Here, we present the application of a novel multi-length scale and multi-method approach to deepen insights into the photoluminescence properties and (photo)chemical reactivity of cadmium reds in oil paintings by combining both well established and new non-invasive/non-destructive analytical techniques, including macro-scale vis-NIR and vibrational spectroscopies and micro-/nano-scale advanced electron microscopy mapping and X-ray methods employing synchrotron radiation and conventional sources. Macro-scale vis-NIR spectroscopy data obtained from the in situ non-invasive analysis of nine masterpieces by Gerardo Dottori, Jackson Pollock and Nicolas de Stael allowed classifying the CdS1-xSex-paints in three groups, according to the relative intensity of the two DLE bands. These outcomes, combined with results from micro-/nano-scale electron microscopy mapping and X-ray analysis of a set of CdS1-xSex powders and artificially aged paint mock-ups, indicated that the relative intensity of DLEs is not affected by the morphology, microstructure and local atomic environment of the pigment particles but it is influenced by the presence of moisture. Furthermore, the extensive study of artificially aged oil paint mock-ups permitted us to provide first evidence of the tendency of cadmium reds toward photo-degradation and to establish that the conversion of CdS1-xSex to CdSO4 and/or oxalates is triggered by the oil binding medium and moisture level and depends on the Se content. Based on these findings, we could interpret the localized presence of CdSO4 and cadmium oxalate as alteration products of the original cadmium red paints in two paintings by Pollock.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Antwerp X-ray Imaging and Spectroscopy (AXIS)
Impact Factor: 3.4
Times cited: 3
DOI: 10.1140/EPJP/S13360-022-02447-7
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“Probing the chemistry of CdS paints in The Scream by in situ noninvasive spectroscopies and synchrotron radiation x-ray techniques”. Monico L, Cartechini L, Rosi F, Chieli A, Grazia C, De Meyer S, Nuyts G, Vanmeert F, Janssens K, Cotte M, De Nolf W, Falkenberg G, Sandu ICA, Tveit ES, Mass J, De Freitas RP, Romani A, Miliani C, Science Advances 6, eaay3514 (2020). http://doi.org/10.1126/SCIADV.AAY3514
Abstract: The degradation of cadmium sulfide (CdS)-based oil paints is a phenomenon potentially threatening the iconic painting The Scream (ca. 1910) by Edvard Munch (Munch Museum, Oslo) that is still poorly understood. Here, we provide evidence for the presence of cadmium sulfate and sulfites as alteration products of the original CdS-based paint and explore the external circumstances and internal factors causing this transformation. Macroscale in situ noninvasive spectroscopy studies of the painting in combination with synchrotron-radiation x-ray microspectroscopy investigations of a microsample and artificially aged mock-ups show that moisture and mobile chlorine compounds are key factors for promoting the oxidation of CdS, while light (photodegradation) plays a less important role. Furthermore, under exposure to humidity, parallel/secondary reactions involving dissolution, migration through the paint, and recrystallization of water-soluble phases of the paint are associated with the formation of cadmium sulfates.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 13.6
Times cited: 4
DOI: 10.1126/SCIADV.AAY3514
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“Interpreting technical evidence from spectral imaging of paintings by Edouard Manet in the Courtauld Gallery”. Amato SR, Burnstock A, Cross M, Janssens K, Rosi F, Cartechini L, Fontana R, Dal Fovo A, Paolantoni M, Grazia C, Romani A, Michelin A, Andraud C, Tournie A, Dik J, X-ray spectrometry
T2 –, MA-XRF Workshop on Developments and Applications of Macro-XRF in, Conservation, Art, and Archeology, SEP 24-25, 2017, Trieste, ITALY 48, 282 (2019). http://doi.org/10.1002/XRS.2828
Abstract: The paintings by edouard Manet in The Courtauld Gallery Dejeuner sur l'herbe (1863-68), Marguerite de Conflans en Toilette de Bal (1870-1880), Banks of the Seine at Argenteuil (1874), and A Bar at the Folies-Bergere (1882) were investigated for the first time using a range of non-invasive in situ analyses. The aims of the study were to investigate the painting techniques and materials used for this group of works and to critically evaluate the technical evidence derived from the integrated use of imaging techniques and portable spectroscopic methods in this context. The paintings were investigated by means of macro X-ray fluorescence (MA-XRF), reflection spectral imaging, portable UV-Vis-NIR spectroscopy, portable Raman spectroscopy, and reflection FTIR. MA-XRF and reflection spectral imaging allowed visualising elements in the compositions that were not visible using traditional methods of technical study. For example, MA-XRF analysis of Dejeuner sur l'herbe revealed elements of the development of the composition that provided new evidence to consider its relationship to other versions of the composition. The study also highlighted questions about the interpretation of elemental distribution maps and spectral images that did not correspond to the reworking visible in X-radiographs. For example, in A Bar at the Folies-Bergere Manet made numerous changes during painting, which were not clearly visualised with any of the techniques used. The research has wider implications for the study of Impressionist paintings, as the results will support technical studies of works by other artists of the period who used similar materials and painting methods.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 1.298
DOI: 10.1002/XRS.2828
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“Synchrotron-based X-ray spectromicroscopy and electron paramagnetic resonance spectroscopy to investigate the redox properties of lead chromate pigments under the effect of visible light”. Monico L, Janssens K, Cotte M, Romani A, Sorace L, Grazia C, Brunetti BG, Miliani C, Journal of analytical atomic spectrometry 30, 1500 (2015). http://doi.org/10.1039/C5JA00091B
Abstract: Light-induced redox processes have been established as the cause of the chromatic alterations of a number of artists' pigments used from the 15th to the 20th century. Despite the fact that a general comprehension of the mechanisms has been provided through the characterization of photo-degraded compounds, both exhaustive information on the wavelength-dependence of the alteration process of the pigments and experimental evidence in how visible light may influence the formation pathways of specific secondary compounds are still lacking. Establishing an analytical protocol for the study of wavelength-dependence of pigments on photo-redox pathways is relevant for the safe illumination of paintings, especially in view of the possible use of spectrally tunable light sources such as white light emitting diodes (WLEDs). In this work, we propose an integrated approach based on a combination of diffuse reflectance UV-visible, synchrotron radiation (SR)-based micro X-ray fluorescence (m-XRF)/X-ray absorption near edge structure (m-XANES) and electron paramagnetic resonance (EPR) spectroscopies to study the photo-redox process of Cr(VI) -> Cr(III) for lead chromate yellows (PbCr1-xSxO4, 0 <= x <= 0.8) under exposure to different monochromatic light. In view of the thin (3-5 mm) alteration layer that is formed at the paint surface after light exposure, SR-based Cr K-edge mu-XANES/mu-XRF analysis was employed to obtain information on the abundance, nature and distribution of the alteration of Cr(III)-compounds at the micrometricscale level. On the other hand, EPR spectroscopy was used as a complementary tool to the SR-based X-ray methods due to its sensitivity for revealing species containing one or more unpaired electrons and for distinguishing different coordination geometries of paramagnetic centers, such as Cr(V)-species. Semi-quantitative indications about the darkening of the paint surface were obtained by UV-Vis spectroscopy. An abundance of reduced Cr down to around 50% was detected at the aged surface of chrome yellow paints. The reduction process was favored not only by wavelengths shorter than 460 nm (i.e., where the pigment shows its maximum absorption) but also by light in the 490-530 nm range. The first evidence of the presence of Cr(V)-intermediates in the Cr(VI) -> Cr(III) reduction reaction allowed the risks of inducing photo-degradation of the 490-530 nm wavelength range to be explained.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.379
Times cited: 17
DOI: 10.1039/C5JA00091B
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