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Abstract: Back-reflection energy-dispersive XRD (BR-EDXRD) is a non-invasive technique that offers extremely high-resolution and insensitivity to surface morphology. It is notably effective in the analysis of cultural heritage objects, where non-invasive analytical techniques are clearly advantageous. In particular, the technique is ideally suited to the analysis of paints, where samples are typically thin, have components that are finely-powdered and can consist of complex phase mixtures. Whole-pattern fitting (i.e. Rietveld or Pawley fitting) to diffraction patterns offers a wealth of information such as chemical composition, polymorphism, phase ratios and microstructural details which can help in authentication, attribution and conservation, as well as yielding insight into historic pigment manufacture, trade and artists’ preferences. Rietveld fitting is challenging for energy-dispersive XRD because incident and diffracted intensities are non-uniform as a function of energy, and pigments and fillers in paints are typically contained in an amorphous matrix with an unknown absorption coefficient. For BR-EDXRD this is exacerbated; the experimental configuration employed utilises an air-gap between sample and detector window which is poorly constrained from sample to sample, making it challenging to model. Herein we present results from a selection of historically relevant paints examined by BR-EDXRD3 (Figure 1a) to establish the limitations and capabilities of the technique, including extraction of accurate lattice parameters, microstructural analysis and phase quantification (Figure 1b). This was achieved by introducing an empirical intensity scaling correction function to allow Rietveld fitting to the BR-EDXRD data.

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Abstract: Chinese porcelains have been in production for hundreds of years and are important evidence for informing our understanding of Chinese history, culture, technology and trade. With this in mind, it is clear that accurate determination of the provenance and authenticity of an object is crucial. However, scientific investigation is limited by the high value of the objects which hinders or precludes destructive or invasive analyses. Famille Rose porcelain was first produced in China in the early 18th century CE. It is characterised by its pink-coloured overglaze enamel arising from the inclusion of colloidal gold (‘Purple of Cassius’) in a glassy matrix, a technique that may have been brought to China by Jesuit missionaries. In conjunction with colloidal gold, opaque enamels such as lead stannate (PbSbO3) and lead arsenates were commonly used. Back-reflection energy-dispersive XRD (BR-EDXRD) offers high-resolution and insensitivity to surface morphology which negates the need for sample preparation. Furthermore, the low incident energies employed make the technique particularly sensitive to the surface layers. In the case of Famille Rose porcelains, this offers the opportunity to selectively study the enamel and glazes. The experimental configuration also allows the concurrent collection of XRF data which can greatly assist in interpretation of BR-EDXRD patterns. In this work BR-EDXRD data were collected from various positions on the piece which indicate the presence of various phases present in the enamel, including Au, Pb2Sn2O6, SnO2 and KPb4(AsO4)3. Furthermore, Co is confirmed to be present in several blue spots by the concurrent XRF measurement, though no Co phases were detected. The significance of these findings is discussed.

Open Access

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Abstract: Purportedly originating from the late Predynastic–Early Dynastic period of ancient Egyptian civilisation (about 3100 BC), the statuette known as “MacGregor Man” was acquired near the site of Naqada in southern Egypt by the Reverend William MacGregor at the end of the 19th century. The Ashmolean Museum (University of Oxford) subsequently purchased the statuette at the sale of MacGregor’s collection in 1922, and it remains one of the most important items in the museum’s Egyptology collection. However, the authenticity of the statuette has been the focus of fierce scholarly debate since it first came to light. At that time there was little with which the object could be compared and a forger would have little source material to copy: some of its features are consistent with securely provenanced statuettes and figurines that were discovered some time after the appearance of MacGregor Man. Several other aspects have caused others to question whether MacGregor Man is genuine. It is carved from what is widely believed to be a basaltic rock; rare in ancient Egypt and its hardness would have made sculpting such a detailed statue exceedingly difficult with the tools available to ancient stonemasons. Also, there are strong indications that MacGregor Man may have been deliberately damaged, possibly in an effort to artificially “antiquate” the statuette (though other explanations are feasible). Despite the sustained interest in MacGregor Man, no mineralogical analysis of the stone it is sculpted from has been carried out to date. Though it has been visually identified as being most likely a basalt, it has so far been impossible to ascertain even this basic information without removing a sample from and thus damaging the statue. Even a basic understanding of the mineralogy of the sample could prove informative since basaltic composition can be diagnostic for determining the region of its origin. Using energy-dispersive X-ray diffraction (EDXRD) in a back-reflection geometry, a non-destructive technique, high-resolution powder diffraction data from several regions were collected at Diamond Light Source (Didcot, Oxfordshire, U.K.) in February 2019. From these data, despite poor powder averaging (resulting from the large crystallite size), we plan to extract crystallographic information such as the minerals present and unit cell dimensions. This will be compared to published data from known Egyptian basalt samples in an attempt to ascertain whether it is Egyptian in origin. The results of this crystallographic analysis will be presented.

Open Access

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Abstract: The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s−1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.

Open Access

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Abstract: Energy-dispersive X-ray diffraction (EDXRD) implemented in a back-reflection geometry is extremely insensitive to sample morphology and positioning even in a high-resolution configuration1,2. This technique allows high-quality XRD analysis of samples that have not been prepared in any way and is therefore completely non-destructive. The experimental technique was implemented on beamline B18 at the Diamond Light Source synchrotron in Oxfordshire, UK. The majority of the experiments in this study were performed with pre-characterised geological materials in order to elucidate the characteristics of this novel technique and to develop the analysis methods. Sample d-spacings were extracted from the data with a typical accuracy of 2 x 10-4 Å, enabling phase identification and the derivation of precise unit-cell parameters which yield insights into the sample material such as the position within a solid solution series. The data is of sufficient quality to allow the investigation of microstructural properties such as crystallite size and shape, and microstrain. A particular highlight was the identification of a specific polytype of a muscovite in an unprepared mica schist sample, avoiding the time-consuming and difficult preparation steps normally required to make this type of identification in a phyllosilicate-containing sample. The technique was also demonstrated in application to a small number of fossil and archaeological samples, including a Cretaceous shark tooth and a Roman glass mosaic tessera; details of these analyses will be given in the presentation. Back-reflection EDXRD implemented in a high-resolution configuration shows great potential in the crystallographic analysis of cultural heritage artefacts and other specimens. Scientific research of archaeological objects is usually conducted either for the purposes of provenancing or as an aid to the formulation of effective conservation strategies. The avoidance of the need to extract samples from high-value and rare objects is a highly-significant advantage, applicable in other potential research areas such as palaeontology, and the study of meteorites and planetary materials brought to Earth by sample-return missions. References 1. G. M. Hansford, “Back-Reflection Energy-Dispersive X-Ray Diffraction: A Novel Diffraction Technique with Almost Complete Insensitivity to Sample Morphology”, J. Appl. Cryst., 44, 514-525 (2011). 2. G. M. Hansford, S. M. R. Turner, P. Degryse and A. J. Shortland, “High-resolution X-ray diffraction with no sample preparation”, Acta Cryst. A73, 293-311 (2017).