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X-ray emission tomography techniques over non-radioactive materials allow to investigate different and important aspects of the matter that are usually not addressable with the standard X-Ray Transmission Tomography, like: density, chemical composition and crystallographic information. However, the quantitative reconstruction of these investigated properties is hindered by additional problems, including the self-attenuation of the emitted radiation. Work has been done in the past, especially for what concerns X-Ray Fluorescence tomography, but it has always just been focused on solving very specific problems. The novelty of this work resides in addressing the problem of induced emission tomography from a much wider perspective, introducing a unified discrete representation, that can be used to modify existing algorithms to reconstruct the data of the different types of experiments. The direct outcome is a clear and easy mathematical description of the implementation details of such algorithms, despite small differences in geometry and other practical aspects. But also the possibility to express the reconstruction as a minimization problem, allowing the use of variational methods, and a more flexible modeling of the noise involved in the detection process. In addition, we look at the results of a few selected simulated data reconstructions, that describe: the effect of physical corrections like the self-attenuation, and the response to noise of the adapted reconstruction algorithms.

Here, we report analyses by synchrotron X-ray fluorescence microscopy of the elemental composition of eight candidate impact features extracted from the Stardust Interstellar Dust Collector (SIDC). Six of the features were unambiguous tracks, and two were crater-like features. Five of the tracks are so-called “midnight” tracks—that is, they had trajectories consistent with an origin either in the interstellar dust stream or as secondaries from impacts on the Sample Return Capsule (SRC). In a companion paper reporting synchrotron X-ray diffraction analyses of ISPE candidates, we show that two of these particles contain natural crystalline materials: the terminal particle of track 30 contains olivine and spinel, and the terminal particle of track 34 contains olivine. Here, we show that the terminal particle of track 30, Orion, shows elemental abundances, normalized to Fe, that are close to CI values, and a complex, fine-grained structure. The terminal particle of track 34, Hylabrook, shows abundances that deviate strongly from CI, but shows little fine structure and is nearly homogenous. The terminal particles of other midnight tracks, 29 and 37, had heavy element abundances below detection threshold. A third, track 28, showed a composition inconsistent with an extraterrestrial origin, but also inconsistent with known spacecraft materials. A sixth track, with a trajectory consistent with secondary ejecta from an impact on one of the spacecraft solar panels, contains abundant Ce and Zn. This is consistent with the known composition of the glass covering the solar panel. Neither crater-like feature is likely to be associated with extraterrestrial materials. We also analyzed blank aerogel samples to characterize background and variability between aerogel tiles. We found significant differences in contamination levels and compositions, emphasizing the need for local background subtraction for accurate quantification.

International audience; The Stardust Interstellar Preliminary Examination team analyzed thirteen Al foils from the NASA Stardust interstellar collector tray in order to locate candidate interstellar dust (ISD) grain impacts. Scanning electron microscope (SEM) images reveal that the foils possess abundant impact crater and crater-like features. Elemental analyses of the crater features, with Auger electron spectroscopy, SEM-based energy dispersive X-ray (EDX) spectroscopy, and scanning transmission electron microscope-based EDX spectroscopy, demonstrate that the majority are either the result of impacting debris fragments from the spacecraft solar panels, or intrinsic defects in the foil. The elemental analyses also reveal that four craters contain residues of a definite extraterrestrial origin, either as interplanetary dust particles or ISD particles. These four craters are designated level 2 interstellar candidates, based on the crater shapes indicative of hypervelocity impacts and the residue compositions inconsistent with spacecraft debris.

A quantification tool for energy-dispersive X-ray fluorescence (ED-XRF) spectral data is presented, based on the application of Monte Carlo simulations in an iterative, inverse manner. Acting as an open-source plug-in to the widespread PyMca package, it provides users with a superior alternative to the fundamental parameter method based built-in quantification tool, taking into account higher order interactions, M-lines and cascade effects. Examples are shown demonstrating the usefulness of our implementation through data recorded at the synchrotron X-ray fluorescence microprobe installed at the HASYLAB Beamline L, Hamburg, Germany.

International audience; The ID21 beamline (European Synchrotron Radiation facility, France) is a multi micro-analytical platform combining X-ray and infrared micro-probes, for characterization of elements, species, molecular groups and crystalline structures in complex materials. Applications are mainly in the fields of cultural heritage, life science, environmental and earth sciences, materials sciences. Here, we first present the status of instruments: (i) the scanning micro-spectroscopy end-station, operating from 2.0 to 9.2 keV, under vacuum and offering cryo conditions, for the acquisition of 2D micro X-ray fluorescence (μXRF) maps, single point micro X-ray Absorption Near Edge Structure (μXANES) spectra and speciation maps with sub-micrometric resolution; (ii) the XANES full-field end-station, operating in the same vacuum and energy conditions, for the acquisition of hyper-spectral radiographs of thin concentrated samples, resulting in speciation maps with micrometric resolution and millimetric field of view; (iii) the scanning micro-X-ray diffraction (μXRD)/μXRF end-station, operating at 8.5 keV, in air, for the acquisition of 2D crystalline phase maps, with micrometric resolution; and (iv) the scanning infrared microscope, operating in the mid-infrared range for the acquisition of molecular maps and some structural maps with micrometric resolution. Recent hardware and software developments are presented, as well as new protocols for improved sample preparation of thin sections. Secondly, a review of recent applications for the study of cultural heritage is presented, illustrated by various examples: determination of the origin of the color in blue Chinese porcelains and in brown Sèvres porcelains; detection of lead in ink on Herculaneum papyri; identification and degradation of modeling materials used by Auguste Rodin and of chrome yellow pigments used by Vincent van Gogh. Cryo capabilities are illustrated by the analysis of plants exposed to chromate solutions. These examples show the variety of materials analyzed, of questions tackled, and particularly the multiple advantages of the ID21 analytical platform for the analysis of ancient and artistic materials.

A nonproprietary software package, "PyMca", primarily developed for X-ray fluorescence analysis offers an easy-to-use interface for calculating maps, by integrating intensity (of X-ray fluorescence, as well as any spectral data) over Regions Of Interest (ROI), by performing per pixel operations or by applying multivariate analysis. Here we show that, while initially developed to analyze hyperspectral two-dimensional (spatial) maps, this tool can be beneficial as well to anyone interested in measuring spectral variations over one or two dimensions, these dimensions being time, temperature, and so on. Different possibilities offered by the software (preprocessing, simultaneous analysis of replicas, of different conditions, ROI calculation, multivariate analysis, determination of reaction rate constant and of Arrhenius plot) are illustrated with two examples. The first example is the Fourier transform infrared spectroscopy (FTIR) follow-up of the saponification of oil by lead compounds. The disappearance of reagent (oil) and formation of products (lead carboxylates and glycerol) can be easily followed and quantified. The second example is a combined extended X-ray absorption fine structure (EXAFS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and mass spectroscopy (MS) analysis of RhAl2O3 catalyst under NO reduction by CO in the presence of O2. It is possible to appreciate, in a single shot, Rh particles' structure and surface changes and gas release and adsorption in the reaction conditions.

This work presents the recent developments of xraylib, an ANSI C library that provides convenient access to a large number of X-ray related databases, with a focus on quantitative X-ray fluorescence applications. The enhancements include improved X-ray fluorescence production cross sections that take into account cascade effects and M-lines, as well as revised line energies, atomic level widths, Compton broadening profiles etc. A full overview of the complete application programming interface is presented.

A user friendly program for X-ray fluorescence analysis has been developed at the European Synchrotron Radiation Facility. The program allows interactive as well as batch processing of large data sets and it is particularly well suited for X-ray imaging. Its implementation of a complete description of the M shell is particularly helpful for analysis of data collected at low energies. The code is platform independent (Linux, Windows, MacOS X, Solaris …) and it is freely available for non-commercial use. Description of the algorithms used and practical examples are presented.

Odontolite or bone turquoise, a turquoise-blue coloured heated fossilised mastodon ivory or bone, is an imitation of the mineral turquoise used for the decoration of medieval art objects. Its colour origin can be ascribed to Mn 5+ traces in a tetrahedral environment of four oxygen atoms in an apatite matrix. The structural environment of Mn was investigated by means of extended X-ray absorption fine structure (EXAFS) in order to shed new light on the colour transformation of fossilised ivory induced by a thermal treatment. This was particularly difficult as the manganese concentration does not exceed trace amounts in fossilised ivory. EXAFS experiments confirm the presence of Mn 2+/3+/4+ ions before and Mn 5+ ions after thermal treatment in fossilised ivory and the location of Mn 5+ ions on a P analogous site in apatite.

Seven particles captured by the Stardust Interstellar Dust Collector and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream. More than 50 spacecraft debris particles were also identified. The interstellar dust candidates are readily distinguished from debris impacts on the basis of elemental composition and/or impact trajectory. The seven candidate interstellar particles are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from any one representative model of interstellar dust inferred from astronomical observations and theory.

Heat-induced color changes of fossilized Miocene mastodon ivory (13–16 Ma) have been known at least since the Middle Ages. Cistercian monks are believed to have created odontolite, a turquoise-blue “gemstone,” by heating mastodon ivory found in Miocene geological layers next to the Pyrrenean chain, France, to use it for the decoration of medieval art objects. This material has been the object of investigations of famous European naturalists and gemmologists, among them Reaumur (1683–1757). Although vivianite [Fe 3 (PO 4 ) 2 ·8H 2 O] is the commonly accepted coloring phase supposed to appear when heating fossilized mastodon ivory, our previous spectroscopic studies using PIXE/PIGE and TEM-EDX demonstrated that the chemical composition of collection odontolite and heated mastodon ivory corresponds to well-crystallized fluorapatite [Ca 5 (PO 4 ) 3 F] containing trace amounts of Fe (230–890 ppm), Mn (220–650 ppm), Ba (160–620 ppm), Pb (40–140 ppm), and U (80–210 ppm). No vivianite has been detected. To provide new insights into the physico-chemical mechanism of the color transformation of fossilized ivory, we used the combination of UV/visible/near-IR reflectance spectroscopy, time-resolved laser-induced luminescence spectroscopy (TRLIF), and X-ray absorption near-edge structure (XANES). Contrary to what had formerly been described as the color origin in odontolite, our study has conclusively identified traces of Mn 5+ by UV/visible/near-IR reflectance spectroscopy, TRLIF, and XANES inside the fluorapatite. Thus, odontolite owes its turquoise-blue color to Mn 5+ ions in a distorted tetrahedral environment of four O 2− ions. XANES also demonstrated oxidation of disordered octahedral Mn 2+ ions to tetrahedral Mn 5+ species in apatite during the heat process. So we give the first evidence of the real color origin in odontolite.

On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (less than 10 km per second) for particles with the ratio of the solar radiation pressure force to the solar gravitational force beta greater than 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 grams per cubic centimeter, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

Using synchrotron-based X-ray diffraction measurements, we identified crystalline material in two particles of extraterrestrial origin extracted from the Stardust Interstellar Dust Collector. The first particle, I1047,1,34 (Hylabrook), consisted of a mosaiced olivine grain approximately 1 mu m in size with internal strain fields up to 0.3%. The unit cell dimensions were a - 4.85 +/- 0.08 angstrom, b - 10.34 +/- 0.16 angstrom, c - 6.08 +/- 0.13 angstrom (2 sigma). The second particle, I1043,1,30 (Orion), contained an olivine grain approximate to 2 mu m in length and > 500 nm in width. It was polycrystalline with both mosaiced domains varying over approximate to 20 degrees and additional unoriented domains, and contained internal strain fields < 1%. The unit cell dimensions of the olivine were a = 4.76 +/- 0.05 angstrom, b = 10.23 +/- 0.10 angstrom, c = 5.99 +/- 0.06 angstrom (2 sigma), which limited the olivine to a forsteritic composition [Fo(65) (2 sigma). Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a = 8.06 +/- 0.08 angstrom (2 sigma). Two additional crystalline phases were present and remained unidentified. An amorphous component appeared to be present in both these particles based on STXM and XRF results reported elsewhere.

Hard X-ray, quantitative, fluorescence elemental imaging was performed on the ID22NI nanoprobe and ID22 microprobe beam lines of the European Synchrotron Research facility (ESRF) in Grenoble, France, on eight interstellar candidate impact features in the framework of the NASA Stardust Interstellar Preliminary Examination (ISPE). Three features were unambiguous tracks, and the other five were identified as possible, but not definite, impact features. Overall, we produced an absolute quantification of elemental abundances in the 15 ? Z ? 30 range by means of corrections of the beam parameters, reference materials, and fundamental atomic parameters. Seven features were ruled out as interstellar dust candidates (ISDC) based on compositional arguments. One of the three tracks, I1043,1,30,0,0, contained, at the time of our analysis, two physically separated, micrometer-sized terminal particles, the most promising ISDCs, Orion and Sirius. We found that the Sirius particle was a fairly homogenous Ni-bearing particle and contained about 33 fg of distributed high-Z elements (Z > 12). Orion was a highly heterogeneous Fe-bearing particle and contained about 59 fg of heavy elements located in hundred nanometer phases, forming an irregular mantle that surrounded a low-Z core. X-ray diffraction (XRD) measurements revealed Sirius to be amorphous, whereas Orion contained partially crystalline material (Gainsforth et al. 2014). Within the mantle, one grain was relatively Fe-Ni-Mn-rich; other zones were relatively Mn-Cr-Ti-rich and may correspond to different spinel populations. For absolute quantification purposes, Orion was assigned to a mineralogical assemblage of forsterite, spinel, and an unknown Fe-bearing phase, while Sirius was most likely composed of an amorphous Mg-bearing material with minor Ni and Fe. Owing to its nearly chondritic abundances of the nonvolatile elements Ca, Ti, Co, and Ni with respect to Fe, in combination with the presence of olivine and spinel as inferred from XRD measurements, Orion had a high probability of being extraterrestrial in origin.

We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and beta-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.

–Here, we report the identification of 69 tracks in approximately 250 cm 2 of aerogelcollectors of the Stardust Interstellar Dust Collector. We identified these tracks throughStardust@home, a distributed internet-based virtual microscope and search engine, in which> 30,000 amateur scientists collectively performed >9 9 10 7 searches on approximately 10 6 fields of view. Using calibration images, we measured individual detection efficiency, andfound that the individual detection efficiency for tracks > 2.5 lm in diameter was >0.6, andwas >0.75 for tracks >3 lm in diameter. Because most fields of view were searched >30times, these results could be combined to yield a theoretical detection efficiency near unity.The initial expectation was that interstellar dust would be captured at very high speed. Theactual tracks discovered in the Stardust collector, however, were due to low-speed impacts,and were morphologically strongly distinct from the calibration images. As a result, thedetection efficiency of these tracks was lower than detection efficiency of calibrationspresented in training, testing, and ongoing calibration. Nevertheless, as calibration imagesbased on low-speed impacts were added later in the project, detection efficiencies for low-speed tracks rose dramatically. We conclude that a massively distributed, calibrated search,with amateur collaborators, is an effective approach to the challenging problem ofidentification of tracks of hypervelocity projectiles captured in aerogel.1510 A. J. Westphal et al.

Under the auspices of the Stardust Interstellar Preliminary Examination, picokeystones extracted from the Stardust Interstellar Dust Collector were examined with synchrotron Fourier transform infrared (FTIR) microscopy to establish whether they contained extraterrestrial organic material. The picokeystones were found to be contaminated with varying concentrations and speciation of organics in the native aerogel, which hindered the search for organics in the interstellar dust candidates. Furthermore, examination of the picokeystones prior to and post X-ray microprobe analyses yielded evidence of beam damage in the form of organic deposition or modification, particularly with hard X-ray synchrotron X-ray fluorescence. From these results, it is clear that considerable care must be taken to interpret any organics that might be in interstellar dust particles. For the interstellar candidates examined thus far, however, there is no clear evidence of extraterrestrial organics associated with the track and/or terminal particles. However, we detected organic matter associated with the terminal particle in Track 37, likely a secondary impact from the Al-deck of the sample return capsule, demonstrating the ability of synchrotron FTIR to detect organic matter in small particles within picokeystones from the Stardust interstellar dust collector.

We report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy-resolution spectra of major rock-forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg-spinel, forsterite, and an iron-bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low-density, amorphous Mg-silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high-speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty-two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X-ray analyses; however, we recorded the effects of synchrotron hard X-ray radiation on I1043,1,30 and I1047,1,34.

International audience; The ID21 Scanning X-ray Microscope (SXM) is optimized for micro-spectroscopy with submicron resolution in the 2 to 9.5 keV energy range. After a brief description of the microscope setup, we present here recent developments, in particular, the latest version of the compact Wavelength Dispersive Spectrometer and the refurbished cryo-stage

This work presents the recent developments of xraylib, an ANSI C library designed to provide convenient access to a large number of X-ray related databases, with a focus on quantitative XRF applications. The discussed enhancements include improved XRF production cross sections that take into account cascade effects and M-lines, as well as revised line energies, atomic level widths, Compton broadening profiles etc. A full overview is presented of the complete API.

Stardust, a NASA Discovery-class mission, was the first sample-return mission to return solid samples from beyond the Moon. Stardust was effectively two missions in one spacecraft: it returned the first materials from a known primitive solar system body, the Jupiter-family comet Wild 2; Stardust also returned a collector that was exposed to the contemporary interstellar dust stream for 200 days during the interplanetary cruise. Both collections present severe technical challenges in sample preparation and in analysis. By far the largest collection is the cometary one: approximately 300 micro g of material was returned from Wild 2, mostly consisting of approx. 1 ng particles embedded in aerogel or captured as residues in craters on aluminum foils. Because of their relatively large size, identification of the impacts of cometary particles in the collection media is straightforward. Reliable techniques have been developed for the extraction of these particles from aerogel. Coordinated analyses are also relatively straightforward, often beginning with synchrotron-based x-ray fluorescence (S-XRF), X-ray Absorption Near-Edge Spectoscopy (XANES) and x-ray diffraction (S-XRD) analyses of particles while still embedded in small extracted wedges of aerogel called ``keystones'', followed by ultramicrotomy and TEM, Scanning Transmission X-ray Microscopy (STXM) and ion microprobe analyses (e.g., Ogliore et al., 2010). Impacts in foils can be readily analyzed by SEM-EDX, and TEM analysis after FIB liftout sample preparation. In contrast, the interstellar dust collection is vastly more challenging. The sample size is approximately six orders of magnitude smaller in total mass. The largest particles are only a few pg in mass, of which there may be only approx.10 in the entire collection. The technical challenges, however, are matched by the scientific importance of the collection. We formed a consortium carry out the Stardust Interstellar Preliminary Examination (ISPE) to carry out an assessment of this collection, partly in order to characterize the collection in sufficient detail so that future investigators could make well-informed sample requests. The ISPE is the sixth PE on extraterrestrial collections carried out with NASA support. Some of the basic questions that we asked were: how many impacts are there in the collector, and what fraction of them have characteristics consistent with extraterrestrial materials? What is the elemental composition of the rock-forming elements? Is there crystalline material? Are there organics? Here we present coordinated microanalyses of particles captured in aerogel, using S-FTIR, S-XRF, STXM, S-XRD; and coordinated microanalyses of residues in aluminum foil, using SEMEDX, Auger spectroscopy, STEM, and ion microprobe. We discuss a novel approach that we employed for identification of tracks in aerogel, and new sample preparation techniques developed during the ISPE. We have identified seven particles - three in aerogel and four in foils - that are most consistent with an interstellar origin. The seven particles exhibit a large diversity in elemental composition. Dynamical evidence, supported supported by laboratory simulations of interstellar dust impacts in aerogel and foils, and numerical modeling of interstellar dust propagation in the heliosphere, suggests that at least some of the particles have high optical cross-section, perhaps due to an aggregate structure. However, the observations are most consistent with a variety of morphologies

Grunewald is a famous German painter of the 16th century, whose celebrity is associated with his unique skill in handling colors. This article presents the analysis of materials used to render a metallic aspect in the Isenhein Altarpiece and the Basel's Crucifixion. Such samples are challenging objects for microanalysis due to both chemical and physical complexity. Their study by synchrotron-based X-ray microscopy techniques was made possible thanks to recent developments carried out at the ID21 beam line (European Synchrotron Radiation Facility, ESRF). A submicron X-ray fluorescence probe revealed the main presence of lead, sulfur, antimony, and calcium. The fluorescence-line interferences (in particular K-lines of sulfur with M-lines of lead, and K-lines of calcium with L-lines of antimony) were resolved with the fitting program, PyMCA. 2D-mapping highlighted the presence of micrometer grains of sulfur and antimony into a lead matrix. XANES measurements were performed at both the sulfur K-edge and the antimony L-edge to refine information from an atomic to a molecular level. Beam stability was a key point in this study to selectively probe micrometer pigment grains, dispersed in the lead matrix. They confirm that the grains are made of stibnite (antimony sulfide), a very atypical pigment. Chemical mapping of sulfides is perfectly correlated with antimony mapping and provides a clear visualization of the stibnite pigments, in addition to their identification. Besides its artistic relevancy, this work aims at illustrating developments of synchrotron X-ray microprobe methods for the chemical characterization and observation of complex and micrometer-scale materials.

International audience; A new X-ray absorption near-edge spectroscopy (XANES) full-field imaging station has been developed, installed and tested on beamline ID21 at the European Synchrotron Radiation Facility (ESRF). The set-up operates in the 2-9 keV energy range and allows for the simultaneous acquisition of up to 4.10(6) XANES spectra over large sample areas with preserved sub-micron spatial resolution. The versatile set-up is compatible with various types of cameras and magnifying objectives. It accommodates spatial resolutions ranging from 0.3 mu m to 1.4 mu m and fields of view from 600 mu m up to 2 mm. The range of potential applications is broad: from geology, cultural heritage, environmental sciences to medicine

X-Ray fluorescence (XRF) is one of the most established techniques for the analysis of works of art. It offers several features—such as non-invasiveness, richness of information, in situ analysis with portable instruments and 2D and 3D micro-imaging when performed at synchrotron sources—which are increasingly used in the field of Cultural Heritage science. However, the complexity of artistic materials may lead into complex XRF spectra. Overlapping of fluorescence emission lines can make XRF analyses prone to error. In this article, we discuss the attributes of the polycapillary-based Wavelength Dispersive X-ray Spectrometer (WDS) developed at the X-ray micro-spectroscopy ESRF beamline, ID21. With spectral resolution of a few tens of eV, this system allows better separation of neighbouring emission lines. Its pros and cons for micro-XRF point analysis, micro-XRF mapping and micro-XANES are addressed, with a particular focus on Cultural Heritage applications. Possible extensions towards micro-RIXS are also discussed.