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International audience; In recent years, we have seen a significant increase in interest in the effects of irradiation used for analytical purposes on art, archaeological, palaeontological and palaeoenvironmental samples and objects. Among the main trends regarding ionising radiations used in X-ray, UV and ion beam experiments, we have observed a greater consistency in the description of the effects of irradiation, a number of quantitative studies, while several works studied in depth the corresponding chemical mechanisms and kinetics. We have also observed the development of analytical strategies and dedicated instruments to better detect and limit the effects of irradiation in real experiments on ancient samples and objects. Emerging trends include detailed mechanistic studies on specific systems, the development of statistical methods to reduce the doses required to study samples, and the development of early warning systems capable of feeding back into the experiment while an acquisition is in progress.

Formation and aggregation of metal carboxylates (metal soaps) can degrade the appearance and integrity of oil paints, challenging efforts to conserve painted works of art. Endeavors to understand the root cause of metal soap formation have been hampered by the limited spatial resolution of Fourier transform infrared microscopy (mu-FTIR). We overcome this limitation using optical photothermal infrared spectroscopy (O-PTIR) and photothermal-induced resonance (PTIR), two novel methods that provide IR spectra with approximate to 500 and approximate to 10 nm spatial resolutions, respectively. The distribution of chemical phases in thin sections from the top layer of a 19th-century painting is investigated at multiple scales (mu-FTIR approximate to 10(2) mu m(3), O-PTIR approximate to 10(-1) mu m(3), PTIR approximate to 10(-5) mu m(3)). The paint samples analyzed here are found to be mixtures of pigments (cobalt green, lead white), cured oil, and a rich array of intermixed, small (often << 0.1 mu m(3)) zinc soap domains. We identify Zn stearate and Zn oleate crystalline soaps with characteristic narrow IR peaks (approximate to 1530-1558 cm(-1)) and a heterogeneous, disordered, water-permeable, tetrahedral zinc soap phase, with a characteristic broad peak centered at approximate to 1596 cm(-1). We show that the high signal-to-noise ratio and spatial resolution afforded by O-PTIR are ideal for identifying phase-separated (or locally concentrated) species with low average concentration, while PTIR provides an unprecedented nanoscale view of distributions and associations of species in paint. This newly accessible nanocompositional information will advance our knowledge of chemical processes in oil paint and will stimulate new art conservation practices.

International audience; Egyptian blue and green are among the oldest synthetic pigments produced by humanity. The two pigments are complex multi-phase copper-based systems synthesised with different protocols from the same raw materials. Since the 2000s, synchrotron X-ray techniques have provided significant new insights on their chemistry and microstructure. However, the potential impact of high flux irradiation of these pigments has not yet been studied despite the fact that it can lead to visual discoloration and less readily observable alterations such as defects formation or redox changes. In this work, we investigate the effects of synchrotron X-ray irradiation on Egyptian blue and green samples. Radiation-induced effects are monitored after irradiation at increasing doses using electron paramagnetic resonance (EPR) spectroscopy at temperatures of 290 K and 30 K. The cupric ion (Cu2+) is in D4h axial geometry in Egyptian blue and in disordered geometry in Egyptian green, which makes the two pigments very easily identifiable by EPR. Egyptian green samples are found to be much more sensitive to X-rays than Egyptian blue. In particular, a browning of the green samples is observed from the lowest doses tested while no color change is detected for the blue ones. Three types of radiation-induced defects are detected after irradiation: E′, non-bonding oxygen hole and aluminum hole centers. Correlations between defect intensity and dose are calculated. Archaeological and modern pigments (whether blue or green) do not show the same reactivity to X-rays, which opens the prospect of using radiation-induced defects as a marker of their history.

Examples of photoluminescence (PL) are being reported with increasing frequency in a wide range of organisms from diverse ecosystems. However, the chemical basis of this PL remains poorly defined, and our understanding of its potential ecological function is still superficial. Amongst mammals, recent analyses have identified free-base porphyrins as the compounds responsible for the reddish ultraviolet-induced photoluminescence (UV-PL) observed in the pelage of springhares and hedgehogs. However, the localization of the pigments within the hair largely remains to be determined. Here we use photoluminescence multispectral imaging emission and excitation spectroscopy to detect, map and characterize porphyrinic compounds in skin appendages in situ. We also document new cases of mammalian UV-PL caused by free-base porphyrins in distantly related species. Spatial distribution of the UV-PL is strongly suggestive of an endogenous origin of the porphyrinic compounds. We argue that reddish UV-PL is predominantly observed in crepuscular and nocturnal mammals because porphyrins are photodegradable. Consequently, this phenomenon may not have a specific function in intra- or interspecific communication but rather represents a byproduct of potentially widespread physiological processes.Co-first authors: Séverine Toussaint and Jasper Ponstein

20200316 H2020-NMBP‐35‐2017 CORES-PD/00253/2012 PD/BD/136678/2018 UIDB/ 50006/2020 UIDP/50006/2020 Cellulose nitrate (CN) is an intrinsically unstable material that puts at risk the preservation of a great variety of objects in heritage collections, also posing threats to human health. For this reason, a detailed investigation of its degradation mechanisms is necessary to develop sustainable conservation strategies. To investigate novel probes of degradation, we implemented deep UV photoluminescence micro spectral-imaging, for the first time, to characterize a corpus of historical systems composed of cellulose nitrate. The analysis of cinematographic films and everyday objects dated from the nineteenth c./early twentieth c. (Perlov's collection), as well as of photo-aged CN and celluloid references allowed the identification of novel markers that correlate with different stages of CN degradation in artworks, providing insight into the role played by plasticizers, fillers, and other additives in stability. By comparison with photoaged references of CN and celluloid (70% CN and 30% camphor), it was possible to correlate camphor concentration with a higher rate of degradation of the cinematographic films. Furthermore, the present study investigates, at the sub-microscale, materials heterogeneity that correlates to the artworks' history, associating the different emission profiles of zinc oxide to specific color formulations used in the late nineteenth and early twentieth centuries. publishersversion published

Les textiles sont perissables dans la plupart des environnements archeologiques. L’un des principaux processus conduisant a la preservation exceptionnelle de leur morphologie resulte du contact avec un objet metallique, un phenomene connu sous le nom de « mineralisation ». Nous presentons ici l’etude d’un textile ancien en lin provenant du site de Nausharo (vallee de l’Indus, Balochistan, Pakistan) et date du IIIe millenaire av. J.-C. Cette etude est integree dans un programme de recherche sur des vestiges textiles mineralises au contact d’objets en cuivre corrodes particulierement anciens, mene avec le CNRS-UMR 7041/ ArScAn, le musee du Louvre et le musee du quai Branly-Jacques Chirac, et mettant a profit de nouvelles approches d’investigation. Il s’agit de la premiere attestation directe de la presence de lin tisse sur le site. L’imagerie tomographique 3D sur synchrotron permet d’acceder a des donnees quantitatives encore inaccessibles sur ces textiles, comme le nombre precis de fibres par fil. Nous avons par ailleurs, a partir d’approches complementaires, detecte la presence de signatures cellulosiques exceptionnellement bien conservees, meme dans le cas d’un tel textile extremement transforme par les mecanismes physico-chimiques d’alteration depuis son depot jusqu’a nos jours. La description de ces restes rares permet d’approfondir l’interpretation archeologique de ces textiles et nous informe egalement sur l’etat d’alteration du support metallique dont la corrosion a joue un role-cle dans la preservation des fibres.

Significance We report on the oldest archaeological textiles studied in detail for the mechanisms leading to their exceptional preservation, issued from archaeological excavations in the Ancient East and from collections of the Louvre Museum. We have studied these fossilized hybrid organic–mineral systems at high spatial resolution, from nano- to microscale, using a combination of nanoinfrared near-field spectroscopy, second harmonic generation microscopy, semiquantitative synchrotron X-ray microtomography, and electron microscopy. We establish a physicochemical pathway leading to their exceptional preservation. We show the joint involvement of the two main long-standing paradigms of mineralization and silicification in the process. We consistently identified “pockets of molecular preservation” with a demonstration of the in-place preservation of cellulose microfibrillar assemblies from SHG microscopy., The understanding of fossilization mechanisms at the nanoscale remains extremely challenging despite its fundamental interest and its implications for paleontology, archaeology, geoscience, and environmental and material sciences. The mineralization mechanism by which cellulosic, keratinous, and silk tissues fossilize in the vicinity of archaeological metal artifacts offers the most exquisite preservation through a mechanism unexplored on the nanoscale. It is at the center of the vast majority of ancient textiles preserved under nonextreme conditions, known through extremely valuable fragments. Here we show the reconstruction of the nanoscale mechanism leading to the preservation of an exceptional collection of ancient cellulosic textiles recovered in the ancient Near East (4,000 to 5,000 years ago). We demonstrate that even the most mineralized fibers, which contain inorganic compounds throughout their histology, enclose preserved cellulosic remains in place. We evidence a process that combines the three steps of water transport of biocidal metal cations and soil solutes, degradation and loss of crystallinity of cellulosic polysaccharides, and silicification.

We report the development of a 3D positioner for the elemental mapping of non-flat surfaces of heritage targets and its implementation in the external beam of the AGLAE accelerator, a joint research activity of the IPERION-CH European program. The positioner operates in two steps: 1) object surface is digitized using a 3D scanner implemented in the beamline. Surface points are interpolated onto a rectangular grid suitable for beam scanning. 2) Object is scanned under the beam using X/Y/Z stages holding a hexapod robot for rotations. During scanning, target surface is positioned with the Z stage and oriented perpendicular to the beam using hexapod rotations. Areas up to 100 × 100 mm2 with a resolution of 50 µm and 30° curvature of can be mapped on objects of 200 mm and 5 kg max. System operation was tested by recording PIXE maps on the polychrome decoration of a curved porcelain pot.

Paper is a complex biopolymer material which contains papermaking additives and often bears inks and other graphic media. Cultural heritage paper-based artefacts are most often deteriorated to some extent. This research explores how intrinsic factors such as constituents and degradation state can impact the modifications incurred in aged papers during and after X-ray examination. To this end laboratory model papers, artificially aged, and 18th and 19th century archival documents, with and without additives (gelatin, calcium carbonate) and iron gallate ink, were exposed to Synchrotron X-ray radiation at doses that were previously shown to incur damage in unaged cotton papers (0.7 to 4 kGy). Glycosidic scissions, hydroxyl free radicals, UV luminescence and yellowing were measured immediately after the irradiation, and were monitored over a period of three years. The depolymerization of cellulose was lower in the aged papers, as well as in the papers containing calcium carbonate and gelatin, than in the unaged fully cellulosic papers. Compared to the papers with no additives, there were more hydroxyl free radicals in the papers with calcium carbonate and slightly less in the gelatin sized papers. UV luminescence and yellowing both appeared post-irradiation, with a delay of several weeks to months, while the intensity of the responses was impacted by the various paper constituents. The papers with iron gallate ink showed limited degradation in the low doses range, most probably due to recombination of the free radicals produced. Doses below 4 kGy did not cause yellowing or UV luminescence of the archival papers within the whole monitoring period. At higher doses (26 to 36 kGy), a slight UV luminescence appeared after 21 months, as well as a slight yellowing after three years, in some of them. No clear correlation between the degradation induced by the irradiation and the constituents in the paper nor its conservation state could be made. The archival papers in good conservation state depolymerized to the same extent as the model papers, while the most degraded archival papers were less impacted than the latter.

International audience; The analysis of cultural heritage artefacts with ionizing radiation has rapidly increased in popularity over the last decades - in particular at synchrotron sources - leading to many fascinating new discoveries. However, the damage inflicted to the materials under study during the irradiation is still largely unknown. Organic samples, such as paper, are especially vulnerable to degradation by X-rays. In this work we quantify the radiation damage on a molecular level and show that the chemical reactions triggered promote cellulose degradation and continueto alter the material for several months after the irradiation took place.

Oil paints comprise pigments, drying oils, and additives that together confer desirable properties, but can react to form metal carboxylates (soaps) that may damage artworks over time. To obtain information on soap formation and aggregation, we introduce a new tapping-mode measurement paradigm for the photothermal induced resonance (PTIR) technique that enables nanoscale IR spectroscopy and imaging on highly heterogenous and rough paint thin sections. PTIR is used in combination with mu-computed tomography and IR microscopy to determine the distribution of metal carboxylates in a 23-year old oil paint of known formulation. Results show that heterogeneous agglomerates of Al-stearate and a Zn-carboxylate complex with Zn-stearate nano-aggregates in proximity are distributed randomly in the paint. The gradients of zinc carboxylates are unrelated to the Al-stearate distribution. These measurements open a new chemically sensitive nanoscale observation window on the distribution of metal soaps that can bring insights for understanding soap formation in oil paint.

Spectacular photoluminescence (PL) phenomena have been increasingly reported in various organisms from diverse ecosystems. However, the chemical basis of this PL remains poorly defined, and its potential ecological function is still blurry, especially in mammals. Here we used state-of-the-art spectroscopy and multispectral imaging techniques to document new cases of mammalian ultraviolet-induced PL (UV-PL) and to identify free-base porphyrins and natural derivatives as the organic compounds responsible for the reddish luminescence observed in the hairs and spines of distantly related species. We argue that pink to red UV-PL is predominantly observed in crepuscular and nocturnal mammals because porphyrins are photodegradable, and that this phenomenon might not have a specific function in intra- or interspecific communication but consists of a byproduct of a widespread physiological condition, overlooked in mammals.Co-first authors: Séverine Toussaint and Jasper Ponstein

Cellulose nitrate (CN) is an intrinsically unstable material that puts at risk the preservation of a great variety of objects in heritage collections, also posing threats to human health. For this reason, a detailed investigation of its degradation mechanisms is necessary to develop sustainable conservation strategies. To investigate novel probes of degradation, we implemented deep UV photoluminescence micro spectral-imaging, for the first time, to characterize a corpus of historical systems composed of cellulose nitrate. The analysis of cinematographic films and everyday objects dated from the 19th c. / early 20th c. (Perlov's collection), as well as of photo-aged CN and celluloid references allowed the identification of novel markers that correlate with different phases of CN degradation in artworks, providing insight into the role played by plasticizers, fillers, and other additives instability. By comparison with photoaged references of CN and celluloid (70% CN and 30% camphor), it was possible to correlate camphor concentration with a higher rate of degradation of the cinematographic films. Furthermore, the present study investigates, at the sub-microscale, materials heterogeneity that correlates to the artworks' history, associating the different emission profiles of zinc oxide to specific color formulations used in the late 19th and early 20th centuries.

International audience; Widespread preservation of fossilized biomolecules in many fossil animals has recently been reported in six studies, based on Raman microspectroscopy. Here, we show that the putative Raman signatures of organic compounds in these fossils are actually instrumental artefacts resulting from intense background luminescence. Raman spectroscopy is based on the detection of photons scattered inelastically by matter upon its interaction with a laser beam. For many natural materials, this interaction also generates a luminescence signal that is often orders of magnitude more intense than the light produced by Raman scattering. Such luminescence, coupled with the transmission properties of the spectrometer, induced quasi-periodic ripples in the measured spectra that have been incorrectly interpreted as Raman signatures of organic molecules. Although several analytical strategies have been developed to overcome this common issue, Raman microspectroscopy as used in the studies questioned here cannot be used to identify fossil biomolecules.

It is shown how soft X-ray nanospectroscopy maps of powders (particle size ∼200 nm) can be analyzed to quantitatively retrieve X-ray linear dichroism (XLD) parameters. A computational modeling procedure is described that can be used in conjunction with Monte Carlo simulations to prove statistical dissimilarity of XLD parameters between different samples., X-ray linear dichroism (XLD) is a fundamental property of many ordered materials that can for instance provide information on the origin of magnetic properties and the existence of differently ordered domains. Conventionally, measurements of XLD are performed on single crystals, crystalline thin films, or highly ordered nanostructure arrays. Here, it is demonstrated how quantitative measurements of XLD can be performed on powders, relying on the random orientation of many particles instead of the controlled orientation of a single ordered structure. The technique is based on a scanning X-ray transmission microscope operated in the soft X-ray regime. The use of a Fresnel zone plate allows X-ray absorption features to be probed at ∼40 nm lateral resolution – a scale small enough to probe the individual crystallites in most powders. Quantitative XLD parameters were then retrieved by determining the intensity distributions of certain diagnostic dichroic absorption features, estimating the angle between their transition dipole moments, and fitting the distributions with four-parameter dichroic models. Analysis of several differently produced ZnO powders shows that the experimentally obtained distributions indeed follow the theoretical model for XLD. Making use of Monte Carlo simulations to estimate uncertainties in the calculated dichroic model parameters, it was established that longer X-ray exposure times lead to a decrease in the amplitude of the XLD effect of ZnO.

International audience; ConspectusThe chemical study of materials from natural history and cultural heritage, which provide information for art history, archeology, or paleontology, presents a series of specific challenges. The complexity of these ancient and historical materials, which are chemically heterogeneous, the product of alteration processes, and inherently not reproducible, is a major obstacle to a thorough understanding of their making and long-term behavior (e.g., fossilization). These challenges required the development of methodologies and instruments coupling imaging and data processing approaches that are optimized for the specific properties of the materials. This Account discusses how these characteristics not only constrain their study but also open up specific innovative avenues for providing key historical information. Synchrotron methods have extensively been used since the late 1990s to study heritage objects, in particular for their potential to provide speciation information from excitation spectroscopies and to image complex heritage objects and samples in two and three dimensions at high resolution. We examine in practice how the identification of key intrinsic chemical specificities has offered fertile ground for the development of novel synchrotron approaches allowing a better stochastic description of the properties of ancient and historical materials. These developments encompass three main aspects: (1) The multiscale heterogeneity of these materials can provide an essential source of information in the development of probes targeting their multiple scales of homogeneity. (2) Chemical alteration can be described in many ways, e.g., by segmenting datasets in a semiquantitative way to jointly inform morphological and chemical transformation pathways. (3) The intrinsic individuality of chemical signatures in artifacts triggers the development of specific strategies, such as those focusing on weak signal detection. We propose a rereading of the advent of these new methodologies for analysis and characterization and examine how they have led to innovative strategies combining materials science, instrument development, history, and data science. In particular, we show that spectral imaging and the search for correlations in image datasets have provided a powerful way to address what archeologists have called the uncertainty and ambiguity of the material record. This approach has implications beyond synchrotron techniques and extends in particular to a series of rapidly developing approaches that couple spectral and spatial information, as in hyperspectral imaging and spatially resolved mass spectrometry. The preeminence of correlations holds promise for the future development of machine learning methods for processing data on historical objects. Beyond heritage, these developments are an original source of inspiration for the study of materials in many related fields, such as environmental, geochemical, or life sciences, which deal with systems whose alteration and heterogeneity cannot be neglected.

A multimodal spectral imaging technique is demonstrated that allows simultaneous acquisition of soft X-ray transmission and X-ray excited optical luminescence. The use of a Fresnel zone plate ensures a lateral resolution of the correlative spectral images of approximately 40 nm., X-ray absorption and optical luminescence can both provide valuable but very different information on the chemical and physical properties of materials. Although it is known that the spectral characteristics of many materials are highly heterogeneous on the micro- and/or nanoscale, no methodology has so far been shown to be capable of spatially resolving both full X-ray absorption and X-ray excited optical luminescence (XEOL) spectra on the nanoscale in a correlative manner. For this purpose, the scanning transmission X-ray microscope at the HERMES beamline of the SOLEIL synchrotron was equipped with an optical detection system capable of recording high-resolution XEOL spectra using a 40 nm soft X-ray probe. The functionality of the system was demonstrated by analyzing ZnO powder dispersions — showing simultaneously the X-ray linear dichroism and XEOL behavior of individual submicrometric ZnO crystallites.

Claims for the widespread preservation of fossilized biomolecules in many fossil animals have recently been reported in six studies, based on Raman microspectroscopy. Here, we show that the putative Raman signatures of organic compounds in these fossils are actually instrumental artefacts resulting from intense background luminescence. Raman spectroscopy relies upon the detection of photons scattered inelastically by matter as a result of its interaction with a laser beam. For many natural materials, this interaction also generates a luminescence signal that is often orders of magnitude more intense than the light produced by Raman scattering. Such luminescence, coupled with the transmission properties of the spectrometer, induced quasi-periodic ripples in the measured spectra that have been incorrectly interpreted as Raman signatures of organic molecules. Although several analytical strategies have been developed to overcome this common issue, Raman microspectroscopy as used in the studies questioned here cannot be used to identify fossil biomolecules.

International audience; X-ray analytical techniques are increasingly being used to study manuscripts and works of art on paper, whether with laboratory equipment or synchrotron sources. However, it is difficult to anticipate the impact of X-ray photons on paper- and cellulose-based artifacts, particularly due to the large variety of their constituents and degradation levels, and the subsequent material multiscale heterogeneity. In this context, this work aims at developing an analytical approach to study the modifications in paper upon synchrotron radiation (SR) X-ray radiation using analytical techniques, which are fully complementary and highly sensitive, yet not frequently used together. At the molecular scale, cellulose chain scissions and hydroxyl free radicals were measured using chromatographic separation techniques (size-exclusion chromatography-multiangle laser light scattering-differential refractive index (SEC-MALS-DRI) and reversed-phase high-performance liquid chromatography-fluorescence detector-diode array detector (RP-HPLC-FLD-DAD)), while the optical properties of paper were characterized using spectroscopy (UV luminescence and diffuse reflectance). These techniques showed different sensitivities toward the detection of changes. The modifications in the cellulosic material were monitored in real time, within a few days, and up to 2 years following the irradiation to define a lowest observed adverse effect dose (LOAED). As paper is a hygroscopic material, the impact of the humidity in the environment was studied using this approach. Three levels of moisture content in the paper, achieved by conditioning the samples and irradiating them at different relative humidities (RHs), were studied (0, 50, 80% RH). It was shown that very low moisture content accelerated molecular and optical modification

17 pages; International audience; Molluscs, the largest marine phylum, display extraordinary shell diversity and sophisticated biomineral architectures. However, mineral-associated biomolecules involved in biomineralization are still poorly characterised.We report the first comprehensive structural and biomolecular study of Spondylus gaederopus, a pectinoid bivalve with a peculiar shell texture. Used since prehistoric times, this is the best-known shell of Europe’s cultural heritage. We find that Spondylus microstructure is very poor in mineral-bound organics, which are mostly intercrystalline and concentrated at the interface between structural layers.Using high-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS) we characterized several shell protein fractions, isolated following different bleaching treatments. Several peptides were identified as well as six shell proteins, which display features and domains typically found in biomineralized tissues, including the prevalence of intrinsically disordered regions. It is very likely that these sequences only partially represent the full proteome of Spondylus, considering the lack of genomics data for this genus and the fact that most of the reconstructed peptides do not match with any known shell proteins, representing consequently lineage-specific sequences.This work sheds light onto the shell matrix involved in the biomineralization in spondylids. Our proteomics data suggest that Spondylus has evolved a shell-forming toolkit, distinct from that of other better studied pectinoids – fine-tuned to produce shell structures with high mechanical properties, while limited in organic content. This study therefore represents an important milestone for future studies on biomineralized skeletons and provides the first reference dataset for forthcoming molecular studies of Spondylus archaeological artifacts.

Le démarrage de la construction du synchrotron SOLEIL au début des années 2000 est l’occasion de poser de manière renouvelée la question de l’apport de ce grand instrument à de nouveaux champs de recherche qui touchent l’ensemble de la société. Les équipes françaises ont été pionnières dans l’étude des objets du patrimoine [1].

Zinc oxide (ZnO) is a II-VI semiconductor that has been used for the last 150 years as an artists' pigment under the name of zinc white. Oil paints containing zinc white are known to be prone to the formation of zinc carboxylates, which can cause protrusions and mechanical failure. In this article, it is demonstrated how a multispectral synchrotron-based deep-UV photoluminescence microimaging technique can be used to show the distribution of zinc soaps on the submicrometer scale and how this information is used to further the understanding of zinc white degradation processes in oil paint. The technique is based on the luminescence of zinc soaps in the near-UV (∼3.65 eV) upon excitation in the deep-UV (4.51 eV), involving transitions that are argued to subsequently involve ligand-to-metal and metal-to-ligand charge transfer with intermediate structural reconfiguration. Because the primary emission peak lies at a higher energy than the band gap of ZnO (3.3 eV), the signal can easily be isolated from the pigment's very intense band gap and trap state emission by employing a multispectral acquisition approach. Moreover, analysis at such short wavelengths, in combination with a UV-transparent optical setup, allows for lateral resolution on the order of 200 nm to be obtained. The unprecedented capabilities of the microimaging technique are illustrated by showing its application to the study of a historical cross section from an early 20th century painting by Piet Mondrian. Revealing the submicrometer distribution of crystalline zinc soaps in this cross section provides new insights that suggest that microfissures, the starting points of paint delamination, are the result of an overall expansion of a heavily saponified zinc white layer.

9 pages; International audience; After the end-Permian crisis and the extinction of their four Paleozoic subclasses, crinoids rapidly recovered. This group is classically believed to have radiated from a small surviving clade and to have diversified during the Middle and Upper Triassic from two lineages. Nevertheless, recent findings suggested that several lineages of crinoids had already diversified during the Early Triassic, and that their diversity has been overlooked. Here we describe a new form of holocrinid, Holocrinus nov. sp., from the earliest Spathian (Early Triassic) of southeastern Idaho (USA). So far, the exceptional completeness of sampled specimens, with skeletal elements of arms and stem in connection, is unique for the Early Triassic. They show that derived morphological features had already evolved ∼1.3 million years after the Permian–Triassic boundary, supporting the scenario of a rapid Early Triassic diversification of crinoids.

13 pages; International audience; After the end-Permian mass extinction, the Early Triassic (∼251.9 to 247 Ma) is characterized by several biotic crises that particularly affected marine faunas; accordingly, marine ecosystems from this unstable interval have been often described as heavily depauperate. This assumption, however, may relate to a biased fossil record. The discovery of taphonomic windows, like Konservat-Lagerstätten, in the Early Triassic would help to better understand the composition and diversity of ecosystems at that time. The Paris Biota (Idaho, USA) is a highly diverse fossil assemblage from the earliest Spathian (early late Olenekian, ∼250.6 Ma), indicating a rapid rediversification for many groups after the end-Permian crisis and pointing toward a remarkably complex marine ecosystem ∼1.3 m.y. after the Permian-Triassic boundary. However, its detailed taphonomy has not yet been investigated. Here we present the mineral characterization of four of its most abundant taxa: discinoid and linguloid brachiopods, leptomitid sponges, and caridean shrimps. For this purpose, we combined data from Raman microspectroscopy, Fourier Transform InfraRed spectroscopy, and SEM-EDXS. Although all taxa were preserved in calcium phosphate, the morphology, structuring and size of crystals are highly dissimilar at a nano- to micrometric scale. In brachiopods, the ultrastructure of calcium phosphate shows unorganized bacillary-like crystals, while in crustaceans their size is considerably smaller and round-shaped. Similar small crystals are observed in sponges. However, the ultrastructure of calcium phosphate in sponges exhibits a well-defined preferential orientation. In addition, sponges show some compressed but preserved three-dimensional features, with an inner surface better preserved. Such analyses are essential to understand the taphonomic pathways enabling exceptional preservation. The further comprehension of preservation features would help to understand potential bias on observed diversity signals and their interpretation.

International audience; The end-Permian mass extinction is the largest global-scale event ever recorded; it also corresponds to the expansion of the Modern Evolutionary Fauna, which will lead to present-day ecosystems. The Early Triassic is thus a pivotal interval in the evolution of many marine groups. An exceptionally well-preserved early Spathian fossil assemblage, the Paris Biota, was recently discovered in southeastern Idaho, USA; it represents the earliest complex marine ecosystem known to date for the post-crisis aftermath. Here we use synchrotron μXRF imaging to retrieve further anatomical, paleobiological and taphonomical data on some of the most intriguing fossils from the Paris Biota, such as contours of the central disc and the full length of arms in an ophiuroid specimen. We also show that multispectral macro-imaging is powerful to reveal or enhance the visualization of some specimens, particularly shrimps, that are barely perceptible under visible and UV lights. The complementary use of both techniques suggests that the actual richness and abundance of organisms in this exceptionally well-preserved Early Triassic ecosystem is likely to remain underestimated, and this situation may be even worse in other less well-preserved spatiotemporal contexts.

International audience; The detailed description of corrosion processes in ancient and historical metal artifacts currently relies on the in-depth study of prepared cross sections. The in-plane elemental and phase distributions can be established from a combination of light and electron microscopy characterization. Here, we show that high-resolution virtual sectioning through synchrotron X-ray microcomputed tomography allows a precise noninvasive 3D description of the distribution of both internal and external mineral phases in whole objects. In fragments of early copper artifacts (third–second millennium BC) from Southern Mesopotamia and the Indus valley, this approach provided essential clues on long-term corrosion processes. Major and minor phases were identified through semiquantitative evaluation of attenuation coefficients using polychromatic X-ray illumination. We found evidence for initially unidentified phases through statistical processing of images. We discuss interpretation of the distribution of these phases. A good correlation between the corrosion phases identified by CT and by invasive BSE-SEM is demonstrated. In addition to the stratigraphy of the copper corrosion compounds, we examine and discuss the variations observed in the attenuation coefficients of Cu(I) phases. Semiquantitative synchrotron X-ray microtomography phase mapping requires no specific sample preparation, in particular polishing or surface finishing, and any material tearing or displacement is avoided. We also provide evidence for the noninvasive observation of phases rapidly altered upon preparation of real cross sections. The method can be applied when cross-sectioning even of minute fragments is impossible.

The Evolution triptych by Piet Mondrian (1911, oil on canvas, Gemeentemuseum Den Haag) presents a case study of a painting that is seriously affected by zinc soap formation, which has resulted in paint delamination and paint loss, particularly in the cadmium yellow paint areas. The paint is extremely fragile, which makes the paintings vulnerable with regard to handling and treatment. This paper focuses on the analytical research of the painting using various state-of-the-art and novel macro- and micro-imaging techniques. Macro X-ray fluorescence scanning (MA-XRF) revealed the presence of cadmium (Cd) and zinc (Zn) in the affected yellow paints. Paint cross sections of both affected and intact paint areas were investigated using light microscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR) micro-imaging, and synchrotron photoluminescence (PL) micro-imaging. With the help of these techniques, the cadmium yellow pigment could be identified as a mixture of cadmium sulfide and cadmium oxalate. The presence of zinc white was established in areas where the yellow paint film is degraded, while the intact areas of yellow paint do not contain any zinc white. In samples of the degraded paints, it was demonstrated that high concentrations of zinc soaps have formed, accumulating at interfaces. This has caused local chemical and physical changes of the paint resulting in delamination between paint layers.

Bart van der Leck, as a member and co-founder of the artistic movement De Stijl, is well-known for his abstract color plane compositions, set on extensive white backgrounds. The white background in The Woodcutters (1928, oil on canvas), which comprises the brightly luminescing semiconductor pigment zinc white, was noticed to exhibit unusual luminescence behavior under UV light. Based on the observation of three distinctly different intensities of green luminescence, it was possible to differentiate between regions within the white background. This observation raised the question whether photoluminescence could be used as a tool to gain insight into different stages of the paint process and the condition of the different paint layers. This study was conducted on the microscale, on three paint cross-sections taken in the differently luminescing regions of the zinc white background. Optical microscopy and scanning electron microscopy – energy dispersive X-ray spectrometry (SEM-EDX) were used in combination with a synchrotron-based multispectral photoluminescence micro-imaging technique to examine the stratigraphy of each cross-section and reveal the photoluminescence behavior of each layer. The submicron spatial resolution and deep-UV excitation energy allowed resolution of individual zinc white particles, as well as thin surface layers which are thought to be caused by the reaction of zinc white with atmospheric contaminants. The results demonstrate how photoluminescence micro-imaging can be used to differentiate between zinc whites from different sources in the multi-layer build-up of a paint cross-section, and explain the origin of the luminescence behavior of The Woodcutters at the macroscale.

We report the development of a 3D positioner for the elemental mapping of non-flat surfaces of heritage targets and its implementation in the external beam of the AGLAE accelerator, a joint research activity of the IPERION-CH European program.The positioner operates in two steps: 1) object surface is digitized using a 3D scanner implemented in the beamline. Surface points are interpolated onto a rectangular grid suitable for beam scanning. 2) Object is scanned under the beam using X/Y/Z stages holding a hexapod robot for rotations. During scanning, target surface is positioned with the Z stage and oriented perpendicular to the beam using hexapod rotations. Areas up to 100 × 100 mm2 with a resolution of 50 µm and 30° curvature of can be mapped on objects of 200 mm and 5 kg max. System operation was tested by recording PIXE maps on the polychrome decoration of a curved porcelain pot.

This paper describes a photoluminescence imaging approach coupled to a synchrotron source (SR-PL imaging) that provides a new, powerful way to probe the processes involved in metal soap formation in paint films, processes that play an important role in the deterioration of paint films in traditional and modern oil paintings.

Photoluminescence spectroscopy is a key method to monitor defects in semiconductors from nanophotonics to solar cell systems. Paradoxically, its great sensitivity to small variations of local environment becomes a handicap for heterogeneous systems, such as are encountered in environmental, medical, ancient materials sciences and engineering. Here we demonstrate that a novel full-field photoluminescence imaging approach allows accessing the spatial distribution of crystal defect fluctuations at the crystallite level across centimetre-wide fields of view. This capacity is illustrated in archaeology and material sciences. The coexistence of two hitherto indistinguishable non-stoichiometric cuprous oxide phases is revealed in a 6,000-year-old amulet from Mehrgarh (Baluchistan, Pakistan), identified as the oldest known artefact made by lost-wax casting and providing a better understanding of this fundamental invention. Low-concentration crystal defect fluctuations are readily mapped within ZnO nanowires. High spatial dynamics-photoluminescence imaging holds great promise for the characterization of bulk heterogeneous systems across multiple disciplines., Photoluminescence is a powerful probe of chemical composition and structure, but it is challenging to image heterogeneous materials over large scale. Thoury et al. develop a full-field imaging approach to map two cuprous oxide phases in the earliest known lost-wax cast artefact manufactured 6,000 years ago.

International audience; The huge number of complex formulations of synthetic dyes and pigments commercialized in the 19th century makes their comprehensive characterization both difficult and fundamental for their successful identifications in artworks. The description of the exact starting composition of a wide collection of reference materials is preliminary to the study of the challenging photo-degradation processes in which most of the early synthetic dyes and pigments are involved. In this paper, four eosin-based lakes, all containing eosin Y, and one also containing eosin B, but differing in the organic and inorganic materials used as fillers, were fully characterized. These formulations were reconstructed on the base of historical recipes from the extensive Wiesel's collection, dated to the 19th century and bought by Dr Kremer (Kremer Pigmente, Germany) in the 1990s. The composition of each formulation was characterized by Fourier transform infrared spectroscopy (FT-IR) and luminescence spectroscopy was used as a probe for their inert-distinction. Reference paint layers were then prepared by casting the lakes in linseed oil, and their ageing and impact on color change was monitored for one year by analyzing two sets of paint model systems by colorimetry. For each system, two sets were prepared and one was stored in the dark while the other exposed to natural light. The material distribution and homogeneity of the samples were tested by Synchrotron Radiation based micro infrared spectroscopy (SR-μ-FT-IR). Finally, an ultra-sensitive method based on Liquid Chromatography coupled with High Resolution Mass Spectrometry (LC-HRMS) allowed us to characterize eosin degradation products detected but never identified before, and to evaluate their kinetics of formation.

Microspectroscopic Investigation of Metal Soaps in Oil Paintings--a Case Study on late 19th Century Cobalt Green ((CoxZn1-xO) Paint

Luminescence multispectral imaging is a developing and promising technique in the fields of conservation science and cultural heritage studies. In this article, we present a new methodology for recording the spatially resolved luminescence properties of objects. This methodology relies on the development of a lab-made multispectral camera setup optimized to collect low-yield luminescence images. In addition to a classic data preprocessing procedure to reduce noise on the data, we present an innovative method, based on a neural network algorithm, that allows us to obtain radiometrically calibrated luminescence spectra with increased spectral resolution from the low-spectral resolution acquisitions. After preliminary corrections, a neural network is trained using the 15-band multispectral luminescence acquisitions and corresponding spot spectroscopy luminescence data. This neural network is then used to retrieve a megapixel multispectral cube between 460 and 710 nm with a 5 nm resolution from a low-spectral-resolution multispectral acquisition. The resulting data are independent from the detection chain of the imaging system (filter transmittance, spectral sensitivity of the lens and optics, etc.). As a result, the image cube provides radiometrically calibrated emission spectra with increased spectral resolution. For each pixel, we can thus retrieve a spectrum comparable to those obtained with conventional luminescence spectroscopy. We apply this method to a panel of lake pigment paints and discuss the pertinence and perspectives of this new approach.

International audience

International audience

The synchrotron characterisation of archaeological and heritage materials has undergone a steep development in the past years, among a range of other advanced characterisation techniques. For synchrotron techniques alone, close to a hundred articles were published in 2011 on such materials, prompting new developments at large scale facilities. However, few publications have discussed the specific characteristics of heritage materials in their advanced spectroscopic and imaging study. Here, we suggest that a greater consideration be put on the specificities of ancient materials and their theoretical implications on the analytical process. In particular, we discuss the importance of the a posteriori framework of the study of heterogeneous materials considered in their historicity as structuring parameters of their study. Major implications are the relevance of trace analyses, those of majors and we suggest, more importantly, the dynamics between both endpoints. The on-going development of multimodal spectral imaging appears as a way to better address corresponding difficulties. Epistemologically, we suggest that a reflexive approach be developed to explain, structure and possibly contribute to narrowing down the field of possible methodological research.

The web directory of IPERION CH instruments and databases aims at providing researchers with information related to resources (instruments, databases and datasets) available within IPERION CH through a package of categories/metadata that help categorising them according to their different dimensions. A database model has been created.

Imaging spectroscopy, the collection of spatially co-registered images in many contiguous spectral bands, has been developed for remote sensing of the Earth utilizing reflectance or luminescence. In this paper we summarize findings on the application of imaging spectroscopy to works of art in order to identify and map artists’ pigments, improve the visualization of preparatory sketches, and identify non-original material. Two types of novel hyperspectral cameras, one operating from the visible to near-infrared (VNIR, 400–900 nm) and the other in the shortwave infrared (SWIR, 950–1700 nm), have been used to collect diffuse reflectance spectral image cubes from a variety of paintings. The resulting cubes (400–1700 nm, 310 spectral bands) were calibrated to reflectance and the resulting spectra compared with point–based spectra collected with a fiber reflectance spectrometer (350–2500 nm). In addition, a calibrated multispectral camera (600–950 nm, eight spectral bands) was used to obtain luminescence spectral image cubes after exciting paintings at blue wavelengths. False–color images obtained from the SWIR imaging system are shown to give improved visualization of changes from paintings having large and complex reworkings, e.g. Pablo Picasso’s The Tragedy (1903). False–color images and reflectance spectra allowed definitive identification of restoration in a late 13th century Sienese painting that cannot be seen by traditional infrared reflectography. Spectral image processing on the reflectance image cubes have been used to identify the primary pigments or pigment mixtures. For example, the primary pigments and their distribution in Picasso’s Peonies (1901) was determined and compared with x-ray fluorescence (XRF) analysis and scanning electron microscopy-energy dispersive x–ray spectroscopy (SEM–EDS). The results show that the combination of both the SWIR reflectance data and the luminescence data provides a more robust ability to assign the pigments than with visible spectroscopy alone. Also highlighted is the utility of reflectance imaging spectroscopy in the SWIR region to better reveal specific paint changes, including changes in the drawings and markings made by the original artist, or changes made by a subsequent conservator such as a fill.

To assess the accuracy of virtual cleaning of Old Master paintings (i.e. digital removal of discolored varnishes), a physical model was developed and experimentally tested using reflectance imaging spectroscopy on three paintings undergoing conservation treatment. The model predicts the reflectance spectra of the painting without varnish or after application of a new varnish from the reflectances of the painting with the aged varnish, given the absorption of the aged varnish and the scattering terms. The resulting color differences between the painting actually and virtually cleaned can approach the perceivable limit. Residual discrepancies are ascribable to spatial variations in the characteristics of the aged varnish (scattering, optical thickness) and the exposed painting (surface roughness). (C) 2015 Optical Society of America

International audience; Synchrotrons have provided significant methods and instruments to study ancient materials from cultural and natural heritages. New ways to visualise (surfacic or volumic) morphologies are developed on the basis of elemental, density and refraction contrasts. They now apply to a wide range of materials, from historic artefacts to paleontological specimens. The tunability of synchrotron beams owing to the high flux and high spectral resolution of photon sources is at the origin of the main chemical speciation capabilities of synchrotron-based techniques. Although, until recently, photon-based speciation was mainly applicable to inorganic materials, novel developments based, for instance, on STXM and deep UV photoluminescence bring new opportunities to study speciation in organic and hybrid materials, such as soaps and organometallics, at a submicrometric spatial resolution over large fields of view. Structural methods are also continuously improved and increasingly applied to hierarchically structured materials for which organisation results either from biological or manufacturing processes. High-definition (spectral) imaging appears as the main driving force of the current trend for new synchrotron techniques for research on cultural and natural heritage materials.