I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[24092]
Open Access
Abstract: Marine archaeological artefacts contain unexpected compounds due to prolonged exposure to the sea. These can remain dormant and embedded within materials until a change in their surrounding environment, such as exposure to oxygen, prompts a transformation. These changes can pose a problem, as acidic compounds are formed which disintegrate the material, or crystals form which physically break the artefact apart. The extent of these transformations is highly heterogeneous due to its dependence on the ability for oxygen to reach and catalyse these reactions. Additionally, these transformations are heavily dependent on the environment the artefact is exposed to, and the pathways available for ingress, either naturally or through previous degradation. This results in materials with a range of different compounds which are often co-located on the macro, micro and nano-scale. Trying to de-convolute these compounds is challenging, and usually requires a suite of complementary techniques to achieve. Here we report on damaging salts found within marine archaeological bricks and show how it is only possible to qualitatively and quantitatively understand what is present by employing a range of analytical techniques, such as XRD, SEM-EDS and SR-XPD. The marine archaeological bricks studied were found to contain a range of different sulfate-based salts, which had grown crystals in preferred orientations. This provides information which will guide further conservation strategies such as how these bricks are stored, conserved and protected in the future.
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May 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[18533, 23341]
Abstract: Energy-dispersive X-ray diffraction (EDXRD) is extremely insensitive to sample morphology when implemented in a back-reflection geometry. The capabilities of this non-invasive technique for cultural heritage applications have been explored at high resolution at the Diamond Light Source synchrotron. The results of the XRD analysis of the pigments in 40 paints, commonly used by 20th century artists, are reported here. It was found that synthetic organic pigments yielded weak diffraction patterns at best, and it was not possible to unambiguously identify any of these pigments. In contrast, the majority of the paints containing inorganic pigments yielded good diffraction patterns amenable to crystallographic analysis. The high resolution of the technique enables the extraction of a range of detailed information: phase identification (including solid solutions), highly accurate unit cell parameters, phase quantification, crystallite size and strain parameters and preferred orientation parameters. The implications of these results for application to real paintings are discussed, along with the possibility to transfer the technique away from the synchrotron and into the laboratory and museum through the use of state-of-the-art microcalorimeter detectors. The results presented demonstrate the exciting potential of the technique for art history and authentication studies, based on the non-invasive acquisition of very high quality crystallographic data.
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Nov 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[23341]
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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Aug 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[23341]
Abstract: Determination of the provenance of marbles is currently carried out by a combination of petrography, stable isotopic analysis and other approaches, with XRD only utilised to detect characteristic trace impurities. However, this procedure requires sampling, and can struggle to differentiate between sources. New, complementary techniques are useful for further elucidation. Back-reflection energy-dispersive XRD (BR-EDXRD) offers high-resolution and insensitivity to surface morphology which negates the need for sample preparation.
Herein we present BR-EDXRD data from marble specimens from several historically relevant marble quarries in the Mediterranean, as well as fragments from several historic marble artefacts. The crystallite size is hugely variable from specimen to specimen (estimated to range from 50 μm to 9 mm), resulting in poor powder averaging (beam spot size ~1 mm). This leads to diffraction peak intensity variation, expected diffraction peaks with no observed intensity and even small peak shifts and asymmetry due to individual crystallite effects. To mitigate this, several spots were measured on each specimen.
In all marble specimens, the data were sufficient to identify a calcite-type carbonate phase, and the lattice parameters of which can be shown to be related to the source quarry. This offers a non-invasive method to discriminate between marble quarries which could be used in conjunction with other techniques. To assess the effect that the poor powder averaging has on the reliability of results, a sample of each marble specimen was powdered and laboratory XRD data were collected and are compared to BR-EDXRD data. Strategies for mitigating poor powder averaging effects in future BR-EDXRD experiments are discussed.
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Aug 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[23341]
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.
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Aug 2021
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[16328]
Open Access
Abstract: Data analysis methods for iron X-ray Absorption Spectroscopy (XAS) can provide extensive information about the oxidation state and co-ordination of an Fe-species. However, the extent to which techniques developed using a single-phase iron sample may be applied to complex, mixed-phase samples formed under real-world conditions is not clear. This work uses a combination of pre-edge fitting and linear combination analysis (LCA) to characterise the near edge region of the X-ray absorption spectrum (XANES) for a set of archaeological iron corrosion samples from a collection of cast iron cannon shot excavated from the Mary Rose shipwreck and compares the data with phase compositions determined by Synchrotron X-ray Powder Diffraction (SXPD). Archaeological powder and cross-section samples were compared to a library of iron standards and diffraction data. The XANES are consistent with previous observations that generation of the chlorinated phase akaganeite, β-FeO(OH,Cl), occurs in those samples which have been removed form passive storage and subjected to active conservation. However, the results show that if any metallic species is present in the sample, the contribution from Fe(0) to the spectral region containing a pre-edge for oxidised iron – Fe(II) and Fe(III) – causes the analysis to be less effective and the conclusions unreliable. Consequently, while the pre-edge fitting methodology may be applied to a mixture of iron oxides or oxyhydroxides, the procedure is inappropriate for a mixed metal-oxide sample without the application of a complimentary technique, such as SXPD.
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Jun 2021
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I18-Microfocus Spectroscopy
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Thomas
Christiansen
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Marine
Cotte
,
Wout
De Nolf
,
Elouan
Mouro
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Juan
Reyes-Herrera
,
Steven
De Meyer
,
Frederik
Vanmeert
,
Nati
Salvado
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Victor
Gonzalez
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Poul Erik
Lindelof
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Kell
Mortensen
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Kim
Ryholt
,
Koen
Janssens
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Sine
Larsen
Diamond Proposal Number(s):
[23348]
Open Access
Abstract: A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro–X-ray fluorescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe2O3) by micro–X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, micro-XRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused “coffee rings” surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb3O4) and lead white (hydrocerussite [Pb3(CO3)2(OH)2] and/or cerussite [PbCO3]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments.
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Oct 2020
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[18676]
Abstract: The in-situ formation of lead-sulfur inorganic compounds in historical oil paintings can have a strong detrimental effect on an artwork’s physical and visual integrity. In this paper, paint micro-samples collected from several paintings from the Rijksmuseum (Amsterdam) and Mauritshuis (The Hague) collections were probed at the micro-scale using a combination of synchrotron micro-XRD and XRD-CT. This permitted to precisely identify the chemical nature of the in-situ formed crystalline compounds as well as to chart their distribution within paint layers at the microscopic level. This provided new information on the origin of the ions involved in the crystallization of the various newly formed mineral lead-sulfur products. The formation of palmierite K2Pb(SO4)2, anglesite PbSO4 and lanarkite Pb2(SO4)O in historical samples can thus be connected to paint stratigraphic build-up, environmental conditions and potential past restoration treatments.
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Jul 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[10104]
Open Access
Abstract: Determining the nature, evolution, and impact of acid‐generating sulfur deposits in the Mary Rose wooden hull is crucial for protecting Henry VIII's famous warship for generations to come. Here, a comprehensive X‐ray absorption near‐edge spectroscopy (XANES) and X‐ray fluorescence (XRF) study sheds vital light on the evolution of complex sulfur‐based compounds lodged in Mary Rose timbers as a function of drying time. Combining insights from infrared spectroscopy correlates the presence of oxidized sulfur species with increased wood degradation via the loss of major wood components (holocellulose). Intriguingly, zinc is found to co‐exist with iron and sulfur in the most degraded wood regions, indicating its potential contributing role to wood degradation. This study provides crucial information on the degradation processes and resulting products within the wood, which can be used to develop remediation strategies to save the Mary Rose.
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May 2020
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Abstract: We present experimental results and FLUKA Monte-Carlo simulations reproducing the counting efficiency and the energy resolution of the cerium-activated yttrium-aluminium-perovskite photon detectors installed on the VESUVIO neutron spectrometer at the ISIS Pulsed Neutron and Muon Source. In particular, we investigate the performance of these detectors in the energy range between 100 keV and 300 keV. In this range, the
-emission of the 197Au resonant analyser foils, installed on VESUVIO to select the energy of scattered neutrons, is predominant. Such photons are currently discarded by the low-level discrimination threshold of the acquisition electronics set to 600 keV. Here, we model the detector crystals for a series of thickness values, and we discuss how 2-cm-thick crystals would significantly reduce the acquisition times with respect to the 6-mm-thick crystals employed at present. Additionally, we show how the signal-to-background ratio can be substantially enhanced by shielding the scintillators with 0.5-mm-thick Pb foils. We finally discuss the improved detection performance on a model sample of interest for Cultural-Heritage applications.
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Apr 2020
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