The use of combined synchrotron radiation micro FT-IR and XRD for the characterization of Romanesque wall paintings

The high analytical sensitivity and high spatial resolution of synchrotron radiation-based techniques, in particular SR-XRD and SR-FT-IR, allows the identification of complex micrometric mixtures of compounds that constitute the different layers of ancient paintings. The reliability of the measurements even with an extremely small amount of sampled material is very high, and this is particularly important when analyzing art works. Furthermore, the micro size (10×10μm for FT-IR and 30 to 50 μm squared spot size for XRD) of the beam enables one to obtain detailed compositional profiles from the different chromatic and preparation layers. The sensitivity of the techniques is high enough for the determination of minor and trace compounds, such as reaction and weathering compounds. We report here the identification of pigments in the Romanesque wall paintings found in situ in the church of Saint Eulàlia of Unha place in the Aran valley (central Pyrenees). During the first centuries of the second millennium numerous religious buildings were built in Western Europe in the Romanesque style. In particular, a great number of churches were built in the Pyrenees, most of which were decorated with wall paintings. Although only a few of these paintings have survived, they represent one of the most important collections of Romanesque art, both for their quantity and quality. A full identification of the pigments, binder, supports, and reaction and weathering compounds has been obtained. The results obtained, in particular aerinite as a pigment, indicate a clear connection between the paintings found in this Occitanian church and the Catalan Romanesque paintings from the south bound of the Pyrenees. PACS 61.10.Nz; 07.85.Qe; 82.80.Gk     

Temperature resolved reproduction of medieval luster

Luster is a golden metallic-like decoration produced on glazed ceramics since early Islamic times (Iraq, 9th AD). Luster is obtained by the reaction of a luster paint and the glaze surface over which it is applied. A temperature-resolved XRD experiment was designed to study the high temperature reactions in the luster paint while the luster layer is formed. The luster paint composition has been made based on the original luster paints found during the excavation of the 13th AD workshop site at Paterna (Valencia). The sulfo-reducing atmosphere created during the decomposition of cinnabar promotes the reduction of Cu²⁺ containing compounds to Cu⁺ and the presence of Hg vapours delays the precipitation of metal silver. Moreover, evidence of the formation of a melt in which the copper and silver-containing compounds dissolve has also been obtained. The thickness of the luster paint applied results in the formation of luster layers of different hues and colours. The use of a mixture of copper and silver paint results in the formation of dark-brown luster layer similar to the ones produced in early Islamic times in Iraq and showed also the characteristic blue iridescences. PACS 81.05.Pj; 81.07.-b; 78.67.-n; 82.39.Wj     

Synchrotron radiation micro-XRD in the study of glaze technology

The production of glass represented an important technological achievement, and it was the starting point for the invention of a large variety of materials, produced by processes involving melting, partial or total, and precipitation of new crystalline compounds during cooling. In particular, those crystallites built-in the glaze due to partial or total insolubility of some elements originally present in the melt (for instance some colourants and opacifiers), as well as those crystallites formed in the glazes resulting from the interaction of the melt and the ceramic surface are subject of the highest interest in the study of glaze technology. Finally, devitrification and weathering gives rise to precipitation of new crystalline compounds closer to the surfaces and interfaces.     

Rates of strong uniform convergence of the k T -occupation time density estimator

In this paper, we study an extension of the k _n nearest neighbor density estimators in continuous time. We obtain the optimal and the superoptimal uniform convergence rates up to a logarithm term on a compact set, in the context of strongly mixing processes.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Extended-ion approximation and pressure shifts inF-band energies

Pressure variation of maximumF-band absorption energies in the halides of lithium, sodium and potassium has been investigated employing the extended-ion approximation for the calculation of theF-electron energy eigenvalues and using values of local compressibility in the neighbourhood of theF-centres which include the effect of vacancy and pressure. The results obtained agree with the experimental results.     

SR-XRD and SR-FTIR study of the alteration of silver foils in medieval paintings

Altarpieces and polychrome carved wood from the fifteenth century AD usually exhibit golden and silvery areas by the application of a very thin foil of metal. The metal foils were normally protected from the atmosphere by a varnish or resin which maybe either preserved or absent. Moreover, they were glued to the background surface by adhesive substances (egg yolk, drying oil or animal glue). The high proportion of the glueing substances often renders the development of reaction compounds. With time, silver alters blacken or simply disappear completely. In this paper, we study the alterations to metal foils from a selection of fifteenth century artworks showing different glueing agents, organic coatings and several degrees of conservation of the organic coatings and metal leafs. The submillimetric layered structure and the high variability and low amount of most of the compounds present in the different layers, as well as their differing nature (organic and inorganic) make the use of micron-sensitive high-resolution techniques essential for their study. In particular, the high resolution, high brilliance and small footprint renders synchrotron radiation most adequate for their study. SR-XRD was performed to identify the reaction compounds formed in the different layers; μFTIR was used at to identify the silver protecting organic coatings, the metal foil glueing layers and the corresponding reaction compounds. The results obtained suggest that atmospheric corrosion is the dominant mechanism, and therefore that the degree of corrosion of the metal foils is mainly related to the conservation state of the protecting coatings.