FS-XANES imaging using the Maia detector is proposed for studying chrome yellows alteration in Va... more FS-XANES imaging using the Maia detector is proposed for studying chrome yellows alteration in Van Gogh artworks.
Annual review of analytical chemistry (Palo Alto, Calif.), 2013
We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were us... more We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were used for nondestructive analysis and characterization of pigments, paint microsamples, and/or entire paintings. We discuss the use of portable laboratory- and synchrotron-based instrumentation and describe several variants of X-ray fluorescence (XRF) analysis used for elemental analysis and imaging and combined with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Macroscopic and microscopic (μ-)XRF variants of this method are suitable for visualizing the elemental distribution of key elements in paint multilayers. Technical innovations such as multielement, large-area XRF detectors have enabled such developments. The use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that take place during natural pigment alteration processes. However, synchrotron-based combinations of μ-XRF, μ-XAS, and μ-XRD are suit...
ABSTRACT The analytical aspects of the investigation of 'Flower Still Life' by Vi... more ABSTRACT The analytical aspects of the investigation of 'Flower Still Life' by Vincent van Gogh and its underlying composition, showing two wrestlers by scanning macro-X-ray Fluorescence Analysis (MA-XRF) was reported. In MA-XRF the painting is excited by an X-ray millibeam to emit X-ray fluorescence radiation. Through the energy of the recorded fluorescence radiation the elements present in the analyzed spot can be identified. The painting was mounted on a motor stage behind the normal experimental table and moved continuously through the beam for scanning. The beam size was defined by a set of slits placed at the end of the experimental table. MA-XRF scans were performed with a step size of 1 mm and a dwell time of 3.6 s. The sample was cross-sectioned and examined using high-resolution microscopic methods. The correction of absorption effects in the Zn-maps allowed to remove otherwise misleading artifacts from hidden layers, so that a more realistic impression of the hidden portrait is gained.
This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Go... more This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam). Noninvasive in situ spectroscopic analysis at several spots on the painting, combined with synchrotron-radiation-based X-ray investigations of two microsamples, revealed the presence of different types of chrome yellow used by Van Gogh, including the lightfast PbCrO4 and the sulfur-rich PbCr1-x Sx O4 (x≈0.5) variety that is known for its high propensity to undergo photoinduced reduction. The products of this degradation process, i.e., Cr(III) compounds, were found at the interface between the paint and the varnish. Selected locations of the painting with the highest risk of color modification by chemical deterioration of chrome yellow are identified, thus calling for careful monitoring in the future.
ABSTRACT Fossil-bearing shale specimens that include sulfides in their compositions are chemicall... more ABSTRACT Fossil-bearing shale specimens that include sulfides in their compositions are chemically reactive and sometimes also mechanically fragile. This decay is often related to iron sulfate efflorescence resulting from the oxidation of sulfide compounds. The processes underlying these degradations are poorly known, thus impeding the elaboration of curative or preventive treatments. The present contribution aims to identify the origin of museum specimen alterations. It focuses on the Flouest collection housed at the Muséum National d’Histoire Naturelle (MNHN, Paris, France) and originating from the Autun Basin (Saône-et-Loire, France, Permian). To evaluate the alteration of MNHN specimens, it appeared necessary to compare their composition with that of unaltered shale so as to identify chemical changes occurring during ageing. Therefore, new material was collected in the Autun Basin, among others on the locality of Muse that corresponds to the same lithostratigraphic unit as that of the MNHN specimens. This material was, if necessary, artificially aged. The first part of this work, presented elsewhere, deals with the use of X-ray diffraction and Mössbauer spectroscopy for characterizing iron reactivity and speciation. It leads to the conclusion that the reactivity of iron in the shale matrix was limited and could not account for the large efflorescence of iron (II) sulfate occurring nearby the fossil. The second part presented here focuses on the use of S K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy for characterizing sulfur speciation and reactivity. Measurements were performed on the shale matrix and on thin layers of maceral found in the proximity of damaged areas. As sulfur may be found in association with calcium or organic matter, complementary techniques were implemented, such as FTIR spectroscopy, Rock-Eval pyrolysis (characterization of organic matter content) and Ca K-edge XANES (analysis of calcium speciation) spectroscopy. It was shown that sulfur is mainly related to thioether, sulfoxide, iron sulfide, and sulfates whereas calcium is mainly bound to carboxylate, carbonate and/or sulfate groups. FTIR analysis of the macerals confirmed the presence of vitrinite on damaged MNHN specimens. The low oxygen content of new shale samples determined by Rock-Eval pyrolysis indicates that the organic matter is well preserved, despite the fact that samples come from outcrop surface. In the newly collected material, sulfur is mainly related to organic sulfides (thioether) with a minor occurrence of iron sulfide. In the shale fraction of damaged MNHN specimens, sulfur is mostly oxidized into a mixture of iron and calcium sulfate. However, in the vitrinite layers of the same specimens, a large proportion of sulfur corresponds to organic sulfides. Also the oxidation of sulfur does not occur homogeneously but preferentially in the shale fraction, probably because this latter is porous whereas vitrinite is not. Artificial ageing of new shale material showed that the oxidation of organic sulfides could be reproduced at 90 °C, 80% of relative humidity. However, the obtained efflorescence almost exclusively corresponds to calcium sulfate whereas iron (II) sulfates are mostly observed on MNHN specimens. The new material collected on site is probably to be questioned, and future studies will have to select new samples with fossil remains. This will be the object of the third part of this work.
ABSTRACT Evaluation of degradation process of biodegradable materials is particularly important i... more ABSTRACT Evaluation of degradation process of biodegradable materials is particularly important in tissue engineering. The aim of this study was to show how 3D imaging technique which combines X-ray absorption microtomography (uCT) and X-ray diffraction microtomography (XRDCT) could be used to examine the in vitro degradation process of polycaprolactone–based composites. The measurements were performed at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) at the ID 22 beamline. Quantitative 3D morphological information withsubmicron resolution was obtained by uCT. The sample-to-detector distance was large enough so that edge-enhancement by refraction of Xrays was utilized (phase contrast imaging). The complementary information on phase distribution, changes in crystallinity and composition during degradation process was obtained by means of XRD-CT. Finally, it was possible to compare uCTand XRD-CT images of the same sample cross-section and demonstrate the capability of the technique for biomedical investigations.
The development of advanced methods for non-destructive selective imaging of painted works of art... more The development of advanced methods for non-destructive selective imaging of painted works of art at the macroscopic level based on radiation in the X-ray and infrared range of the electromagnetic spectrum are concisely reviewed. Such methods allow to either record depth-selective, element-selective or species-selective images of entire paintings. Camera-based 'full field' methods (that record the image data in parallel) can be discerned next to scanning methods (that build up distributions in a sequential manner by scanning a beam of radiation over the surface of an artefact). Six methods are discussed: on the one hand, macroscopic X-ray fluorescence and X-ray diffraction imaging and X-ray laminography and on the other hand macroscopic Mid and Near Infrared hyper-and full spectral imaging and Optical Coherence Tomography. These methods can be considered to be improved versions of the well-established imaging methods employed worldwide for examination of paintings, i.e., X-ray radiography and Infrared reflectography. Possibilities and limitations of these new imaging techniques are outlined.
Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several di... more Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several discoloration phenomena. These transformations are either described as darkening of the pigment caused by the formation of either plattnerite (β-PbO2 ) or galena (PbS) or as whitening by which red lead is converted into anglesite (PbSO4 ) or (hydro)cerussite (2 PbCO3 ⋅Pb(OH)2 ; PbCO3 ). X-ray powder diffraction tomography, a powerful analytical method that allows visualization of the internal distribution of different crystalline compounds in complex samples, was used to investigate a microscopic paint sample from a Van Gogh painting. A very rare lead mineral, plumbonacrite (3 PbCO3 ⋅ Pb(OH)2 ⋅PbO), was revealed to be present. This is the first reported occurrence of this compound in a painting dating from before the mid 20th century. It constitutes the missing link between on the one hand the photoinduced reduction of red lead and on the other hand (hydro)cerussite, and thus sheds new light on the whitening of red lead.
Imaging of crystalline phase distributions in heterogeneous materials, either plane projected or ... more Imaging of crystalline phase distributions in heterogeneous materials, either plane projected or in virtual cross sections of the object under investigation, can be achieved by scanning X-ray powder diffraction employing X-ray micro beams and X-ray-sensitive area detectors. Software exists to convert the two-dimensional powder diffraction patterns that are recorded by these detectors to one-dimensional diffractograms, which may be analysed by the broad variety of powder diffraction software developed by the crystallography community. However, employing these tools for the construction of crystalline phase distribution maps proves to be very difficult, especially when employing micro-focused X-ray beams, as most diffraction software tools have mainly been developed having structure solution in mind and are not suitable for phase imaging purposes.XRDUAhas been developed to facilitate the execution of the complete sequence of data reduction and interpretation steps required to convert ...
A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray a... more A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray absorption near edge structure (XANES) measurements at the Cr K-edge already allowed us to establish that the photo-reduction of chromates to Cr(III) compounds is the cause of darkening of chrome yellow pigments (PbCr 1Àx S x O 4 , 0 # x # 0.8) in a number of paintings by Vincent van Gogh and in corresponding artificially aged paint models. A silicon drift detector (SDD) was employed to record the Cr-K XRF radiation in these X-ray micro beam-based measurements. However, in view of the limited count rate capabilities and collection solid angle of a single device, m-XRF and m-XANES employing single element SDDs (or similar) are primarily suited for collection of spectral data from individual points.
FS-XANES imaging using the Maia detector is proposed for studying chrome yellows alteration in Va... more FS-XANES imaging using the Maia detector is proposed for studying chrome yellows alteration in Van Gogh artworks.
Annual review of analytical chemistry (Palo Alto, Calif.), 2013
We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were us... more We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were used for nondestructive analysis and characterization of pigments, paint microsamples, and/or entire paintings. We discuss the use of portable laboratory- and synchrotron-based instrumentation and describe several variants of X-ray fluorescence (XRF) analysis used for elemental analysis and imaging and combined with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Macroscopic and microscopic (μ-)XRF variants of this method are suitable for visualizing the elemental distribution of key elements in paint multilayers. Technical innovations such as multielement, large-area XRF detectors have enabled such developments. The use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that take place during natural pigment alteration processes. However, synchrotron-based combinations of μ-XRF, μ-XAS, and μ-XRD are suit...
ABSTRACT The analytical aspects of the investigation of 'Flower Still Life' by Vi... more ABSTRACT The analytical aspects of the investigation of 'Flower Still Life' by Vincent van Gogh and its underlying composition, showing two wrestlers by scanning macro-X-ray Fluorescence Analysis (MA-XRF) was reported. In MA-XRF the painting is excited by an X-ray millibeam to emit X-ray fluorescence radiation. Through the energy of the recorded fluorescence radiation the elements present in the analyzed spot can be identified. The painting was mounted on a motor stage behind the normal experimental table and moved continuously through the beam for scanning. The beam size was defined by a set of slits placed at the end of the experimental table. MA-XRF scans were performed with a step size of 1 mm and a dwell time of 3.6 s. The sample was cross-sectioned and examined using high-resolution microscopic methods. The correction of absorption effects in the Zn-maps allowed to remove otherwise misleading artifacts from hidden layers, so that a more realistic impression of the hidden portrait is gained.
This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Go... more This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam). Noninvasive in situ spectroscopic analysis at several spots on the painting, combined with synchrotron-radiation-based X-ray investigations of two microsamples, revealed the presence of different types of chrome yellow used by Van Gogh, including the lightfast PbCrO4 and the sulfur-rich PbCr1-x Sx O4 (x≈0.5) variety that is known for its high propensity to undergo photoinduced reduction. The products of this degradation process, i.e., Cr(III) compounds, were found at the interface between the paint and the varnish. Selected locations of the painting with the highest risk of color modification by chemical deterioration of chrome yellow are identified, thus calling for careful monitoring in the future.
ABSTRACT Fossil-bearing shale specimens that include sulfides in their compositions are chemicall... more ABSTRACT Fossil-bearing shale specimens that include sulfides in their compositions are chemically reactive and sometimes also mechanically fragile. This decay is often related to iron sulfate efflorescence resulting from the oxidation of sulfide compounds. The processes underlying these degradations are poorly known, thus impeding the elaboration of curative or preventive treatments. The present contribution aims to identify the origin of museum specimen alterations. It focuses on the Flouest collection housed at the Muséum National d’Histoire Naturelle (MNHN, Paris, France) and originating from the Autun Basin (Saône-et-Loire, France, Permian). To evaluate the alteration of MNHN specimens, it appeared necessary to compare their composition with that of unaltered shale so as to identify chemical changes occurring during ageing. Therefore, new material was collected in the Autun Basin, among others on the locality of Muse that corresponds to the same lithostratigraphic unit as that of the MNHN specimens. This material was, if necessary, artificially aged. The first part of this work, presented elsewhere, deals with the use of X-ray diffraction and Mössbauer spectroscopy for characterizing iron reactivity and speciation. It leads to the conclusion that the reactivity of iron in the shale matrix was limited and could not account for the large efflorescence of iron (II) sulfate occurring nearby the fossil. The second part presented here focuses on the use of S K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy for characterizing sulfur speciation and reactivity. Measurements were performed on the shale matrix and on thin layers of maceral found in the proximity of damaged areas. As sulfur may be found in association with calcium or organic matter, complementary techniques were implemented, such as FTIR spectroscopy, Rock-Eval pyrolysis (characterization of organic matter content) and Ca K-edge XANES (analysis of calcium speciation) spectroscopy. It was shown that sulfur is mainly related to thioether, sulfoxide, iron sulfide, and sulfates whereas calcium is mainly bound to carboxylate, carbonate and/or sulfate groups. FTIR analysis of the macerals confirmed the presence of vitrinite on damaged MNHN specimens. The low oxygen content of new shale samples determined by Rock-Eval pyrolysis indicates that the organic matter is well preserved, despite the fact that samples come from outcrop surface. In the newly collected material, sulfur is mainly related to organic sulfides (thioether) with a minor occurrence of iron sulfide. In the shale fraction of damaged MNHN specimens, sulfur is mostly oxidized into a mixture of iron and calcium sulfate. However, in the vitrinite layers of the same specimens, a large proportion of sulfur corresponds to organic sulfides. Also the oxidation of sulfur does not occur homogeneously but preferentially in the shale fraction, probably because this latter is porous whereas vitrinite is not. Artificial ageing of new shale material showed that the oxidation of organic sulfides could be reproduced at 90 °C, 80% of relative humidity. However, the obtained efflorescence almost exclusively corresponds to calcium sulfate whereas iron (II) sulfates are mostly observed on MNHN specimens. The new material collected on site is probably to be questioned, and future studies will have to select new samples with fossil remains. This will be the object of the third part of this work.
ABSTRACT Evaluation of degradation process of biodegradable materials is particularly important i... more ABSTRACT Evaluation of degradation process of biodegradable materials is particularly important in tissue engineering. The aim of this study was to show how 3D imaging technique which combines X-ray absorption microtomography (uCT) and X-ray diffraction microtomography (XRDCT) could be used to examine the in vitro degradation process of polycaprolactone–based composites. The measurements were performed at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) at the ID 22 beamline. Quantitative 3D morphological information withsubmicron resolution was obtained by uCT. The sample-to-detector distance was large enough so that edge-enhancement by refraction of Xrays was utilized (phase contrast imaging). The complementary information on phase distribution, changes in crystallinity and composition during degradation process was obtained by means of XRD-CT. Finally, it was possible to compare uCTand XRD-CT images of the same sample cross-section and demonstrate the capability of the technique for biomedical investigations.
The development of advanced methods for non-destructive selective imaging of painted works of art... more The development of advanced methods for non-destructive selective imaging of painted works of art at the macroscopic level based on radiation in the X-ray and infrared range of the electromagnetic spectrum are concisely reviewed. Such methods allow to either record depth-selective, element-selective or species-selective images of entire paintings. Camera-based 'full field' methods (that record the image data in parallel) can be discerned next to scanning methods (that build up distributions in a sequential manner by scanning a beam of radiation over the surface of an artefact). Six methods are discussed: on the one hand, macroscopic X-ray fluorescence and X-ray diffraction imaging and X-ray laminography and on the other hand macroscopic Mid and Near Infrared hyper-and full spectral imaging and Optical Coherence Tomography. These methods can be considered to be improved versions of the well-established imaging methods employed worldwide for examination of paintings, i.e., X-ray radiography and Infrared reflectography. Possibilities and limitations of these new imaging techniques are outlined.
Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several di... more Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several discoloration phenomena. These transformations are either described as darkening of the pigment caused by the formation of either plattnerite (β-PbO2 ) or galena (PbS) or as whitening by which red lead is converted into anglesite (PbSO4 ) or (hydro)cerussite (2 PbCO3 ⋅Pb(OH)2 ; PbCO3 ). X-ray powder diffraction tomography, a powerful analytical method that allows visualization of the internal distribution of different crystalline compounds in complex samples, was used to investigate a microscopic paint sample from a Van Gogh painting. A very rare lead mineral, plumbonacrite (3 PbCO3 ⋅ Pb(OH)2 ⋅PbO), was revealed to be present. This is the first reported occurrence of this compound in a painting dating from before the mid 20th century. It constitutes the missing link between on the one hand the photoinduced reduction of red lead and on the other hand (hydro)cerussite, and thus sheds new light on the whitening of red lead.
Imaging of crystalline phase distributions in heterogeneous materials, either plane projected or ... more Imaging of crystalline phase distributions in heterogeneous materials, either plane projected or in virtual cross sections of the object under investigation, can be achieved by scanning X-ray powder diffraction employing X-ray micro beams and X-ray-sensitive area detectors. Software exists to convert the two-dimensional powder diffraction patterns that are recorded by these detectors to one-dimensional diffractograms, which may be analysed by the broad variety of powder diffraction software developed by the crystallography community. However, employing these tools for the construction of crystalline phase distribution maps proves to be very difficult, especially when employing micro-focused X-ray beams, as most diffraction software tools have mainly been developed having structure solution in mind and are not suitable for phase imaging purposes.XRDUAhas been developed to facilitate the execution of the complete sequence of data reduction and interpretation steps required to convert ...
A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray a... more A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray absorption near edge structure (XANES) measurements at the Cr K-edge already allowed us to establish that the photo-reduction of chromates to Cr(III) compounds is the cause of darkening of chrome yellow pigments (PbCr 1Àx S x O 4 , 0 # x # 0.8) in a number of paintings by Vincent van Gogh and in corresponding artificially aged paint models. A silicon drift detector (SDD) was employed to record the Cr-K XRF radiation in these X-ray micro beam-based measurements. However, in view of the limited count rate capabilities and collection solid angle of a single device, m-XRF and m-XANES employing single element SDDs (or similar) are primarily suited for collection of spectral data from individual points.
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