Study of an archeological opaque red glass bead from China by XRD,XRF, and XANES

As a kind of rare archeological founding in China, red decorative beads (300–400 ad ) were discovered in Leijiaping, Badong County, Hubei, China. For the first time, this paper reports an advanced structural analysis of glass beads using micro synchrotron X‐ray near‐edge absorption spectroscopy. The results show that in spite of being opaque, the red bead is made of glass containing two forms of copper atoms, including 0⁺ and 1⁺. In combination with X‐ray diffraction results, it is advised that the mechanism of red coloration mainly comes from metallic copper. This paper indicates that micro synchrotron X‐ray near‐edge absorption spectroscopy is an outstanding and advanced technology to study ancient glass objects with nondestructive mode. Copyright © 2012 John Wiley & Sons, Ltd.     

A XANES study of chromophores in archaeological glass

We applied X-ray absorption near edge spectroscopy (XANES) to obtain information on the origin of glass colour of several archaeological samples and on the oxidation conditions employed during their production. We studied a series of selected glass fragments—mainly from excavated primary and secondary production centres and dated to the first millennium AD—containing iron and manganese in a wide compositional range. In most of the studied samples iron is rather oxidised, while Mn K-edge XANES data show that, in all the studied glasses, Mn is mainly present in its reduced form (predominantly 2+), with the possible subordinate presence of Mn³⁺. The most oxidised samples are the HIMT (high iron manganese titanium) glasses, while the less oxidised ones belong to the primary natron glass series from the early Islamic tank furnaces at Bet Eliezer (Israel), and to the series coming from a Roman glass workshop excavated in Basinghall Street, London. In these glasses, iron is approximately equally distributed over the 2+ and 3+ oxidation states. The XANES analyses of two glasses which had been deliberately decolourized using Sb- and Mn-based decolourizers demonstrate that Sb is more effective than Mn as oxidant.     

The blue of iron in mineral pigments: a Fe K-edge XANES study of vivianite

Iron is a powerful chromophore element whose pigmenting properties were the first to be recognized among transition metals. The interest in blue iron minerals as pigments for painting was enhanced with the use of vivianite—a natural hydrated ferrous phosphate, Fe₃(PO₄)₂?8H₂O—which in medieval Europe became an alternative to the expensive lapis lazuli, (Na,?Ca)₄(AlSiO₄)₃(SO₄,?Cl,?S), a member of the ultramarines whose appreciated blue tone is due to the presence of sulfur polyanions. Conversely, vivianite coloring is attributed to the intervalence charge transfer (IVCT) Fe²⁺–Fe³⁺ that in later decades was studied by optical techniques and Mössbauer spectroscopy. However, the aging of blue vivianite pigments in old paintings has become a serious concern for conservators, but the aging process still awaits a satisfactory explanation. As an input to this problem, an X-ray absorption near-edge structure (XANES) study at the Fe K-edge of vivianite with different colors and origins was undertaken at the European Synchrotron Radiation Facility using the instrumental facilities of beamline ID-21. The analysis of pre-edge features corroborates previous data on the origin of vivianite color and emphasizes the need for a precautious assessment of iron speciation on the exclusive basis of XANES data. Actual results are discussed and further work is outlined.     

Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

X‐ray absorption near‐edge spectroscopy (XANES) at the Mn K‐edge was used to investigate the environment of Mn in situ within the growth increments of the long‐lived freshwater bivalve species Diplodon chilensis patagonicus. Single XANES spectra and Mn Kα fluorescence distributions were acquired at submillimetre resolution (up to 100 µm × 50 µm), at Mn concentrations below the weight percent range (100–1000 µg g^?1) in a high Ca matrix. The position and intensity of the pre‐edge feature in the shell spectrum resembles best that of the Mn(II)‐bearing reference compounds, suggesting that this is the oxidation state of Mn in the bivalve shells. By comparison with the XANES spectra of selected standard compounds, hypotheses about Mn speciation in the shell are also reported. In particular, different factors, such as provenance, ontogenetic age, variable Mn‐concentrations or seasonal shell deposition seem not to influence the speciation of the metal in this bivalve species.     

Copper resinate: an XPS study of degradation

In this paper, we describe an X-ray photoelectron spectroscopy (XPS) study of copper resinate, a transparent green glaze that is coloured by copper salts of resin acids. This pigment was used in Europe in the fifteenth and sixteenth centuries, but it does not seem to be a usual feature of the palette anywhere after the end of the sixteenth century, because its tendency to discolour was already widely known by artists. An essential prerequisite for the restoration of works of art is the understanding of the effects of various climatic parameters on the deterioration process. For this reason, pictorial models of copper resinate in linseed oil, capable of simulating the ancient paintings on mobile supports, were prepared and aged in a climatic chamber, under different conditions such as exposure to UV radiations, humidity and different concentration of chemical pollutants (NO₂ and SO₂).All the samples were investigated by XPS and the data obtained were evaluated in order to estimate aging effects as well as mechanisms of degradation. On these paint layers damage induced by X-ray irradiation was also verified. PACS 79.60.-i; 61.80.Cb; 81.40.Cd     

Copper diffusion in ion-exchanged soda-lime glass

Cu-alkali ion exchange in silicate glasses gives rise to a peculiar copper distribution, with the presence of both the Cu²⁺ and Cu⁺ oxidation states. Grazing incidence X-ray absorption near-edge structure spectroscopy and secondary ion mass spectrometry were performed on different ion-exchanged samples. The results show that the Cu²⁺/Cu⁺ ratio is strongly depth-dependent. The relative presence of the two species throughout the exchanged region turns out to be governed by their different diffusion regimes, while the chemistry of the red-ox process is shown to play a minor role. A phenomenological model is proposed to describe the diffusion process. PACS 61.10.Ht; 61.43.Fs; 82.65.+r; 67.80.Mg     

Calcium in ancient glazes and glasses: a XAFS study

Ceramic tiles used to manufacture artistic panels during the XVI to the XVIII centuries were decorated with high-lead soda-lime glazes, incorporating a diversity of chromophore cations, as ascertained by SRXRF (synchrotron radiation X-ray fluorescence). Previous X-ray absorption spectroscopy (XAS) studies have shown that sodium and lead are hosted by the glassy matrix in those glazes. However, the possible role of calcium as a modifier of the tetrahedral silica network is not fully clarified, despite being recognized that calcium cations alter some fundamental properties of glazes, namely transparency. An X-ray absorption fine structure (XAFS) study of glazes with varied colorings was therefore undertaken at Ca K- and L-edges. Well crystallized oxide minerals were used to model distinct coordination environments by oxygen atoms – close to octahedral geometry in calcite and dodecahedral in gypsum – while fluorite was chosen to mimic ideal cubic coordination. A first XAS approach suggested a minor variation in the energy separation between L₂–L₃ absorption edges when comparing blue and yellow glazes, irrespective of the period of manufacture. A further study on the X-ray absorption near-edge structure (XANES) carried out at the K-edge corroborated this difference and, along with the theoretical spectra modeling performed with the FEFF code, allowed interpreting of the Ca 1s absorption spectra of glazes as arising from a non-regular high-coordination environment within the silica matrix. PACS  61.43.Fs; 41.60.Ap; 61.10.Ht     

Retroemission by a glass bead monolayer for high-sensitivity, long-range imaging of upconverting phosphors

We introduce a retroemitter (REM) device comprising a planar glass bead set placed on a luminescent material substrate, which converges an excitation beam into a set of foci (voxels). The in-voxel emission is collimated by the beads, and propagates upstream over the long range, unlike the out-of-voxel emission spreading in all angles. The REM signal contrast is characterized as a function of incidence and observation angles and propagation distance. REM signal contrasts of approximately 20 and 1600 were found for the organic fluorescent dye and upconverting phosphor substrates, respectively. In the latter case, nonlinear optical signal enhancement plays a role in addition to the retroemission effect. This allows centimeter-scale REM patterns to be read out at the meter-scale distance using eye-safe sub-mW/cm(2) excitation intensities.     

Copper diffusion in copper sulfide: a systematic study

Copper sulfide Cu_2−xS is a model mineral for chalcogenides because of the existence of a non-stoichiometric compounds series in the range Cu₂S - CuS in which properties change with x. For this reason, we have studied the influence of the mineral composition on the diffusion in this solid. Electrochemical Impedance Spectroscopy (EIS) applied to Cu_2-xS/cupric sulfate electrolyte was the main investigation technique. It enabled us to work at the equilibrium potential at which the composition is fixed and known. Changing the composition by electrochemically removing (or adding) a known amount of Cu, we were able to determine the chemical diffusion coefficient of copper in the composition range (from x=0 to 0.066). In this work, we present the results obtained in the chalcocite and djurleite phases. These results were compared to other values reported in the literature. From this systematic study we discuss various diffusion mechanisms. Our observations support that in chalcocite and djurleite Cu diffuses via a vacancy mechanism. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Frozen capillary waves on glass surfaces: an AFM study

Using atomic force microscopy on silica and float glass surfaces, we give evidence that the roughness of melted glass surfaces can be quantitatively accounted for by frozen capillary waves. In this framework the height spatial correlations are shown to obey a logarithmic scaling law; the identification of this behaviour allows to estimate the ratio kT_F/πγ where k is the Boltzmann constant, γ the interface tension and T_F the temperature corresponding to the “freezing” of the capillary waves. Variations of interface tension and (to a lesser extent) temperatures of annealing treatments are shown to be directly measurable from a statistical analysis of the roughness spectrum of the glass surfaces.     

Raman spectroscopy as a rapid screening method for ancient plain window glass

The aim of this paper is to highlight the potential of Raman spectroscopy as a fast screening method for large amounts of glass samples. Besides the dedicated research of specific glass collections during the last ten years, a broad corpus of archaeological window glass still needs to be investigated. For many sites, the amount of excavated glass artefacts is enormous and a selection of the most appropriate samples for chemical analysis is necessary. A classification can be made on the basis of the typical Raman signatures for the different kinds of glasses (alkali glass, high‐lime low‐alkali (HLLA) glass, Pb‐rich glass). Even in case of strong fluorescence, an uncomplicated treatment (normalisation) of the measured signals makes it possible to distinguish between the different types of glass. The preliminary screening of glass artefacts with Raman spectroscopy is a useful tool in the study of historical glass and can already answer some questions about provenance, period of production and authenticity of the glass samples. Copyright © 2010 John Wiley & Sons, Ltd.     

XANES study of 3d oxides: Dependence on crystal structure

XANES measurements are reported for a number of transition metal oxides. Oxide phases, in which the transition element could be widely varied (within the 3d series) while preserving the crystal structure, were systematically examined. The materials examined include monoxides, perovskites, zircons and spinels. For those samples of a given oxide phase, the near edge spectra are nearly identical but spectra for different phases are dissimilar. These observations are consistent with the simplest view of the x-ray absorption process, namely that dipole selection rules are obeyed and spectral features predominately result from transitions between the K shell and empty states with p-character.     

Raman spectroscopy of copper nanoparticle‐containing glass matrices: ancient red stained‐glass windows

A selection of red‐flashed and red‐coated medieval potash lime and 19th century soda lime stained glass pieces were studied in the laboratory using different instruments and laser wavelengths, both at lower and higher than the surface plasmon resonance (SPR) of copper. The Raman signatures of the transparent glass matrix and the red glass layers are discussed and compared with those recorded on model glasses containing a dispersion of Cu⁰ nanoparticles. Evidence is given that the conformation of the silica network in the vicinity of the metal nanoparticles differs from that of the glass matrix. Hematite and carbon traces are evidenced in the Cu⁰‐rich layers, which is consistent with the use of a combination of a reducing atmosphere and redox couples to control the growth of metallic copper particles. Copyright © 2009 John Wiley & Sons, Ltd.     

XANES study on the valence transitions in cerium oxide nanoparticles

The aim of this work is determination of Ce environment and valence state in Cerium oxide nanopartices prepared by the microemulsion method. X-ray absorption near-edge structure measurements at Ce L3 edge were performed on the nanoparticles as a function of annealing temperature,ranging from 298K to 873K under air condition.The experimental results support the conclusion that Ce ion,in the investigated systems,is in trivalence state when the annealing temperature is below 473K.As the temperature increases up to 623K,the XANEs spectrum shows the coexistence of Ce^3 and Ce^4 states.When the temperature is higher than 623K,the spectra become identical to that of CeO2 with a distinct double-peak structure,corresponding to the Ce^4 state.     

Mössbauer study of the glass transition in a metallic glass

The glass transition in the pseudo-binary metallic glass Zr₆₇Ni₁₀Cu₂₃ doped with 0.5 at.%⁵⁷Fe has been studied by Mössbauer spectroscopy. The glass transition appears as a sudden drop in the recoil-free fraction and an increase in the linewidth, consistent with changes in both the specific heat and the thermal expansion coefficient. The glass transition temperature determined from the change in the temperature dependence of the hyperfine parameters is in agreement with the value obtained from calorimetry. The results are discussed and compared with those of conventional glasses.     

The effect of CO2 on the speciation of bromine in low‐temperature geological solutions: an XANES study

CO₂‐rich solutions are common in geological environments. An XANES (X‐ray absorption near‐edge structure) study of Br in CO₂‐bearing synthetic fluid inclusions has revealed that Br exhibits a strong pre‐edge feature at temperatures from 298 to 423 K. Br in CO₂‐free solutions does not show such a feature. The feature becomes smaller and disappears as temperature increases, but reappears when temperature is reduced. The size of the feature increases with increasing X(CO₂) in the fluid inclusion, where X(CO₂) is the mole fraction of CO₂ in the solution [n_CO2/(n_CO2 + n_H2O + n_RbBr); n indicates the number of moles]. The pre‐edge feature is similar to that shown by covalently bonded Br, but observed and calculated concentrations of plausible Br‐bearing covalent compounds (Br₂, CH₃Br and HBr) are vanishingly small. An alternative possibility is that CO₂ affects the hydration of Br sufficiently that the charge density changes to favour the 1s–p level transitions that are thought to cause the pre‐edge peak. The distance between the first two post‐edge maxima in the XANES also decreases with increasing X(CO₂). This is attributed to a CO₂‐related decrease in the polarity of the solvent. The proposed causes of the observed features are not integrated into existing geochemical models; thus CO₂‐bearing solutions could be predicted poorly by such models, with significant consequences for models of geological processes such as ore‐formation and metamorphism.     

Vanadium K‐edge XANES in vanadium‐bearing model compounds: a full multiple scattering study

A systematic study is presented on a set of vanadium‐bearing model compounds, representative of the most common V coordination geometries and oxidation states, analysed by means of vanadium K‐edge X‐ray absorption near‐edge spectroscopy calculations in the full multiple scattering (FMS) framework. Analysis and calibration of the free parameters of the theory under the muffin‐tin approximation (muffin‐tin overlap and interstitial potential) have been carried out by fitting the experimental spectra using the MXAN program. The analysis shows a correlation of the fit parameters with the V coordination geometry and oxidation state. By making use of this correlation it is possible to approach the study of unknown V‐bearing compounds with useful preliminary information.     

Synthesis and Raman study on needlelike silicates in ancient Chinese Pb‐Ba glass in Qin and Han dynasties

Two ancient green Chinese Pb‐Ba glass (Qin and Han dynasties) were studied with Raman microspectroscopy, scanning electron microscopy, and energy dispersive X‐ray spectrometry. Some needlelike silicates were found in the samples and inferred as BaSiO₃, BaSi₂O₅, and PbSiO₃ according to the results of energy dispersive X‐ray spectrometry analysis. Then BaSiO₃, BaSi₂O₅, and PbSiO₃ were synthetized in laboratory in order to obtain their Raman spectra. Through comparative study, the needlelike silicates in the ancient Pb‐Ba glass samples were proved to be PbSiO₃, BaSiO₃, and Al₂O₃. According to the ternary phase diagram analysis, a mechanism of local element enrichment was put forward for the barium silicate needlelike silicates (by‐products) formation in the ancient Pb‐Ba glass. Copyright © 2014 John Wiley & Sons, Ltd.     

Computational study of redox active centres of blue copper proteins: a computational DFT study

Active sites of blue copper proteins in both reduced and oxidized states were studied at the Density Functional Theory (DFT) level. Two families of these redox sites were examined: the Type A centres with methionine ligand as fourth residue and the Type B with glutamine residue. Constrained and full optimizations were performed on the protein data bank structures in vacuo and in implicit solvent model simulating protein and water environments. It was found that the redox sites do not possess optimum geometries regardless of the oxidation state. The axial Cu-ligand bond elongates/shortens in the fully optimized Cu(I)/Cu(II) complexes. The reduced centres have a tendency to decrease the coordination number, while a trend to form four ‘equivalent’ bonds is preferred in the oxidized centres. Comparison of the full and constrained optimizations also revealed that the A centres exhibit lower relaxation energies. In the constrained structures, a higher ionization potential was predicted for the A centres when compared with the B centres regardless of the influence of environment. The calculated relative difference of the redox potentials between various A and B centres is in good agreement with the experimental data. In the fully optimized complexes, the redox properties are dependent on the environment but usually higher IP for the B centres is predicted. Partial charges, MOs, and spin density distributions (obtained by natural population analysis) were analysed together with calculated electron paramagnetic resonance (EPR) spectra for deeper understanding of the results obtained.