Non-destructive analysis of pigments in a triptych by Marten de Vos

The Fine Arts Museum in Seville conserves an especially wide group of paintings from the 16th century Spanish art, among which one of the highest importance is a triptych attributed to Marten de Vos. One of the panels was recently restored, which opened a possibility for its material and technical analysis. For this research, only non-destructive techniques have been used: ultraviolet light, infrared reflectography, and X-ray fluorescence. The ultraviolet exam showed wide areas of later interventions, which were confirmed by X-ray fluorescence results. By infrared reflectography it was possible to observe under-drawings and some pentimenti. The X-ray fluorescence results identified inorganic pigments, common for that period of time: lead white, yellow, and red ochres, lead–tin yellow, vermilion, a green copper based pigment, azurite, smalt as De Vos’s basic blue pigment, umber, and an organic black pigment, probably bone black.     

Analysis of ferroelectric switching in sodium nitrite:poly(vinyl alcohol) nanocomposite films

The Fourier transform infrared (FTIR) spectra and switching current response in sodium nitrite:poly(vinyl alcohol) nanocomposite films have been studied as a function of composition of NaNO₂. The switching current data fitted well to infinite-grain model (IGM) in the region t<t _s and to finite-grain model (FGM) in the region t≥t _s . The microscopic parameters like the dimensionality, the domain wall velocity, and the nucleation rate have been evaluated which provide more physical insight of the switching phenomena in the composite films. The polarization current and nucleation rate are optimum in 50 wt.% composite film and have been discussed in terms of grain size and strain variations with the composition. The effect of applied field and pulse width variation on the switching behavior of 50 wt.% composition has also been studied. The exponential field dependence of the domain wall velocity and the nucleation rate indicate that nucleation mechanism is responsible for switching phenomena in the composite films. The writing pulse width affects significantly on the switching behavior of the composite films.     

A study on red lead degradation in a medieval manuscript Lorvão Apocalypse (1189)

The mechanisms of red lead degradation were studied in a medieval Portuguese codex, Lorvão Apocalypse (1189), by Raman microscopy (µ‐Raman) and micro‐X‐ray diffraction (µ‐XRD). The range of pigments found for the illuminations is mainly limited to vermilion, orpiment and red lead. Micro‐Fourier transform infrared spectroscopy (µ‐FTIR) determined that the pigments were applied in a proteinaceous binding medium. In the red and orange colours, arsenic (As) was determined, by micro‐energy dispersive X‐ray fluorescence (µ‐EDXRF), to be ranging 1–4% (wt %). For those colours, lead white and calcium carbonate were found as fillers whereas orpiment was applied as a pure pigment. Raman microscopy identified, unequivocally, the degradation product of red lead as galena [lead (II) sulphide, PbS]. To determine the main factors affecting red lead degradation, a set of accelerating ageing experiments was designed to assess the influence of extenders and of the two other pigments, vermilion and orpiment. The experiments were followed by µ‐Raman, µ‐EDXRF and XRD. Raman microscopy results for the simulation of degradation of red lead, in the presence of orpiment, are in agreement to what was found in the Lorvão Apocalypse, galena being the main degradation product; also in common is a Raman band at ca. 810 cm⁻¹, which was attributed to a lead arsenate compound. It was concluded that in Lorvão Apocalypse, the degradation of red lead was a result of its reaction with orpiment. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman diagnostics of heterogeneous chemical processes

The suitability of cw Raman spectroscopy for characterization of mass transport phenomena in connection with heterogeneous chemical processes is demonstrated for the example of the catalytic hydrogenation of acetylene. Temperature and concentration profiles in a model reactor were derived simultaneously from H₂ pure rotational lines and from the most intenseQ branches of C₂H₂ and of C₂H₄. The temperature dependence of the band contours has been considered; by careful calibration the systematic error of the derived concentration values is limited to less than 2%. The measurements allow the separation of the effects of thermal diffusion and of the reaction.     

Assessment of Raman microscopy coupled with principal component analysis to examine egg yolk–pigment interaction based on the protein C?H stretching region (3100–2800 cm−1)

This work seeks to identify the slight changes in the characteristic C H stretching region (3100–2800 cm⁻¹) of a protein‐based binder and fatty acid esters from egg yolk, which may occur in complex paint samples due to the presence of particular pigments. To date, this protein region—where historic pigments do not show characteristic Raman bands—has not been used to identify possible interactions between painting materials, in spite of its potential due to the mentioned feature. This study is based on the investigation of pure egg yolk model samples and tempera model samples prepared by mixing this binder with some historic pigments (cinnabar, raw Sienna, lead white, gypsum, calcite, azurite, lapis lazuli and smalt) as binary samples. All samples were analyzed in this region by Raman microscopy (RM) coupled with principal component analysis (PCA) for three color groups (red, white and blue) separately. The results show relevant spectral changes in the C H stretching region of amino acids and polyunsaturated fatty acids esters of the egg yolk binder, particularly in the azurite, lead white and gypsum‐based tempera samples. Lesser interactions were discerned in the tempera samples made with smalt, as well as shift in the region of polyunsaturated fatty acid esters of the egg yolk binder in the cinnabar and raw Sienna‐based tempera paintings. No interactions were recognized between the egg yolk and the pigments calcite and lapis lazuli. The effectiveness of applying RM combined with PCA for identifying interaction processes between binders and pigments is demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure and photocatalytic properties of copper-doped rutile TiO2 prepared by a low-temperature process

Copper-doped titania with variable Cu/Ti ratios have been prepared via a simple aqueous-phase method at 85 °C. The obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectra analysis. The photocatalytic properties of the products were tested by photocatalytic degradation of aqueous brilliant red X-3B solution. The results showed that the sample with 2% copper doping has the best photocatalytic activity, which is 3 times that of undoped rutile titania. The effect of the doped copper on the structure and property of TiO₂ has also been discussed.     

High-resolution laser spectroscopy on H2 at 97–98 nm

A narrowband tunable eXtreme UltraViolet (XUV) laser source is used for a high resolution study of the Lyman (B ¹ _u ⁺ X ¹ _g ⁺ ) band system of molecular hydrogen. Seven rotational transitions of two vibrational bands, (10,0) and (11,0), in the wavelength range from 97.2–98.3 nm have been investigated for the first time under sub-Doppler molecular beam conditions. A calibration procedure using the I₂ standard in the visible yielded an absolute frequency accuracy of 0.02 cm^–1. The obtained H₂ transition frequencies provide a calibration standard in the extreme ultraviolet wavelength region.     

Solvent solute interactions probed by picosecond transient Raman spectroscopy:S 1 1,4-diphenyl-1,3-butadiene in the linear alkanes

We present theS ₁ Raman spectra of 1,4-DiPhenyl-1,3-Butadiene (DPB) in a series of linear alkanes (pentane, hexane, heptane, octane, decane, and dodecane). Bands assignable to both the 1¹ B _u and 2¹ A _g states are present, suggesting that the state we are observing in solution is a mixed state with both 1¹ B _u and 2¹ A _g character. The relative intensities of several bands associated with C_oC_o stretching motions in the 2¹ A _g and 1¹ B _u states change systematically through the solvent series. The relative intensity changes reflect a changing distribution ofs-trans conformers inS ₁ DPB as the solvent is varied. We suggest that the distribution ofs-trans conformers inS ₁ DPB controls the nature of the mixing between the 2¹ A _g and 1¹ B _u states and that the distribution of conformers is controlled by the solvent viscosity. Changes in the peak position and bandwidth of the phenyl C=C stretch with delay reflect vibrational relaxation processes inS ¹ DPB. We observe anomolous behavior in pentane that we attribute to the effect of the solvent structure on the ability of DPB to exchange energy with pentane.     

Sublevel spectroscopy of alkali atoms in superfluid helium

We report the results of optical pumping and optical detection of magnetic resonance of alkali atoms (Cs and Rb) in superfluid helium. The magnetic resonances between the ground-state Zeeman sublevels and hyperfine levels are observed through monitoring theD ₁ fluorescence by means of the optical-rf double resonance technique. Although the ground stateg values in superfluid helium are the same as in vacuum within the experimental error, the hyperfine constant of the ground state of the Cs atom in superfluid helium is found to be slightly larger than in vacuum. Coherent transient spectroscopy is also performed.     

Facile synthesis and phase control of copper chalcogenides with different morphologies

A series of stoichiometric and nonstoichiometric copper–chalcogenide nanocrystallines with different morphologies, e.g., extremely high aspect ratio nanofibers (Cu₉S₈), tubular structure (Cu _x S (x=∼1.86–1.96), nanorods (CuS, Cu₃₁S₁₆), platelets (β-CuSe, Cu₃Se₂), rope-like Cu₃Se₂, as well as spherical nanoparticles (Cu₇Se₄, Cu_2−x Se), have been successfully synthesized in 20 vol% water and 80 vol% organic solvents mixture under mild conditions. The products were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The studies of the optical properties revealed that the copper chalcogenides have a wide absorption in the range of about 400–700 nm, with accessional IR band. Systematic studies showed that the mixture of 20 vol% water and 80 vol% organic solvents played a key role in controlling the copper chalcogenides with different morphologies and phases.     

Polarization spectroscopy applied to C2 detection in a flame

The detection of C₂ radicals in a premixed acetylene-oxygen flame by using polarization spectroscopy is reported. The signal was recorded in the Swan system,d ³ II _g–a ₃ II _u (0, 0), using a pulsed dye laser. The spectrum shows a very good signal-to-noise ratio with clearly resolved rotational structures of theP andR triplets. The dependence of the signal on the pump-beam polarization was also studied. The spatial distribution of the signal from C₂ radicals in the flame was measured as a demonstration of the use of polarization spectroscopy in combustion diagnostics.     

Effects of nanocracks on the magnetic and electrical properties of single crystals

An investigation of the physical properties of La_0.8Sr_0.2MnO₃ single crystals grown by the molten zone technique is realized close to the metal-to-insulator transition temperature (T_MI). In this paper, we review the effect of the structural defects through magnetotransport and local magnetic microstructures. From electron microscopy observations, some ‘nanocrack’ defects (i.e. defects at a nanometer scale) were found, essentially in the center part of the single crystals. At room temperature, magnetic force microscopy measurements have shown that the absence of defects allowed a magnetic ordering of the domains at the crystal edge, which is the best-crystallized region. In addition, the magnetization loops have permitted us to verify that the crystal was ferromagnetically weaker in the center. On analyzing the electrical resistivity data, we observed in the linear current regime a sensitive variation of the resistivity due to defects, by comparing the center and the edge of the material at T_MI. Additionally, at strong current, non-linearity phenomena have been supposed to be related to local heating. Finally, we discuss the structural disorder effect on the relaxation of the ferromagnetic domains.     

A theoretical spectroscopic study of single ammonia molecules adsorbed on the surface of fcc-type argon clusters. Surface effects on the ν 2 vibration-inversion mode

Ammonia monomers have been adsorbed on argon clusters at low temperature K by Rohmund and Huisken [#!frfh97!#] using the pick-up technique. They measured the spectrum of the NH₃ molecules in the region of the umbrella mode. Two broad bands centered around 970 and 1000 cm^-1 with finer details were observed. The authors attempted to interpret the obtained spectrum on the basis of the free rotation motions of the molecules. In this paper semi-empirical atom-atom potential energy calculations are performed for the ammonia monomer adsorbed on a rigid face-centered-cubic (fcc)-type surface of the argon cluster. In the equilibrium position of the rigid molecule on the cluster surface the orientational potential energy surface exhibits two quasi-equivalent minima separated by a potential barrier of about 100 cm^-1. The symmetry of the molecular vibration-inversion double-well potential is destroyed; the inversion motion is then forbidden in the ground state. On the basis of the two adsorption orientations, the vibrational frequency shifts are calculated and the obtained infrared bar-spectrum agrees with the experimental one. Received 6 April 1999 and Received in final form 19 July 1999     

Microanalytical investigation of degradation issues in Byzantine wall paintings

The St. Euthymius wall paintings, in the Cathedral of Thessaloniki, dated 1303 AD., are stylistically attributed to the School of Panselinos, one of the most important painters of Palaeologean Art. An in situ non-invasive study has been carried out as part of a MOLAB project (a mobile laboratory accessible through the Eu-ARTECH project, funded by the EC 6th FP) combining different analytical techniques such as XRF, mid-FTIR and UV-vis diffuse reflectance spectroscopy. It was during this comprehensive in situ study that certain scientific queries were raised about sensitive areas, where indications of the phenomena of decay requested further attention. A subsequent laboratory study of selected cross-sections using microscopic analysis with μFTIR, SEM-EDS and μRaman, further confirmed the identification of only the atypical in situ observations. The comparative interpretation of all respective results on the specific regions of interest permitted the identification of several degradation phenomena which justify certain aesthetic or stylistic incoherences in the representations. Namely, (i) thermal dehydration of the yellow ochre explaining the reddish appearance of the flesh tones and halos as an accidental effect of the fire; (ii) thermal degradation of azurite converted to tenorite explaining the atypical instance of dark lightings on the purple garments; (iii) degradation of red lead employed in the lightings of the red garments; (iv) widespread presence of oxalates in the paint surface. PACS  87.64.Je; 87.64.Rr; 87.64.Ee     

High-accuracy frequency atlas of 13C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to Doppler-free transitions of the ν₁ + ν₃ and ν₁ + ν₂ + ν₄ + ν₅ combination bands of ¹³C₂H₂. The Allan deviation σ/f for a laser locked to line P(10) of the former band follows a slope of 1.6 × 10⁻¹²τ^−1/2, reaching a minimum of 5.7 × 10⁻¹⁴ at τ = 4000 s. The absolute frequencies of 61 lines of the ν₁ + ν₃ band and 43 lines of the ν₁ + ν₂ + ν₄ + ν₅ band, covering the spectral region 1520 nm to 1552 nm, have been measured by use of a combined frequency chain and femtosecond comb, together with a passive optical frequency comb generator. The mean uncertainties for the line frequencies within each band are 1.4 kHz for the ν₁ + ν₃ band and 1.9 kHz for the ν₁ + ν₂ + ν₄ + ν₅ band, representing improvements on the precision of previously published data by factors of 100 and 10⁴, respectively. Improved values of the rotational constant B″ and centrifugal distortion coefficients D″, H″ and L″ of the vibrational ground state are presented.This article is published with the permission of the Controller of HMSO and the Queen’s Printer of Scotland     

Aging,rejuvenation, and memory phenomena in a lead-based relaxor ferroelectric

Isothermal aging and temperature cycle experiments were done on the relaxor ferroelectric lead magnesium niobate mixed with 10% lead titanate (PMN-10PT) around and below the diffuse maximum of the dielectric loss. With increasing aging time t_w the isothermal evolution of the linear susceptibility follows a power law and does not show frequency scaling. The non-linear susceptibility, however, obeys nearly perfect ωt _w-scaling. After aging the sample at a single temperature we observed both rejuvenation and memory effects in temperature cycle experiments. This observation indicates symmetric behavior in the sense that it shows up irrespective of whether cooling with subsequent re-heating or heating with subsequent re-cooling was performed. The memory effect is absent if subsequent to aging the temperature is increased significantly above that corresponding to the maximum in the dielectric loss. The symmetric behavior within negative and positive temperature cycles under these conditions can be rationalized by the notion of movable domain walls. These become fixed in their configuration on a large spatial scale while more flexible wall segments still show re-conformation processes when cooling or heating the sample after aging. Received 18 December 2001 and Received in final form 28 January 2002     

Effects of inert gases on the degenerate four-wave-mixing spectrum of NO2

We describe the effects of He, Ar and N₂ on the resonant degenerate four-wave-mixing spectrum of NO₂. We report results obtained using the phase-conjugate and forward-geometry experimental configurations for various laser intensities and bandwidths. We find that the effect of buffer-gas pressure on the reflectivity of the laser-induced grating depends critically on the relative value of the laser intensityI to the saturation parameterI _sat. WhenI I _sat the four-wave-mixing signal initially decreases with increasing buffer-gas pressure. However, at pressures above ca. 100 Torr the signal increases. WhenI I _sat the signal is found to increase with buffer-gas pressure even at the lowest pressures studied. These observations do not agree with the standard model of degenerate four-wave mixing in the gas phase. We have investigated the source of these effects by employing different polarisation geometries of the pump and probe laser fields, and conclude that thermal gratings are responsible for the increase in signal observed at high buffer-gas pressure. This conclusion is supported by a simple gas kinetic model.     

An authentication case study: Antonio Palomino versus Vicente Guillo paintings in the vaulted ceiling of the Sant Joan del Mercat church (Valencia,Spain)

In 1695, the Valencian artist Vicente Guillo was engaged in painting the vault of the Sant Joan del Mercat church in Valencia, Spain. After preliminary work was carried out, his contract was cancelled. In 1697, Antonio Palomino, renowned for the publication of his technical treatise entitled El Museo Pictorio y Escala Optica, was finally selected as the painter in charge of decorating the vaulted ceiling of Sant Joan del Mercat. This paper reports an analytical study focused on the characterisation and discrimination of the palette and painting procedures used by Palomino and Guillo in the frescoes of Sant Joan del Mercat. For this purpose, Raman spectroscopy combined with light microscopy, scanning electron microscopy–X‐ray microanalysis, voltammetry of microparticles, X‐ray diffraction, Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry has been employed. The use of gypsum as stucco material for the ground layers contrasts with the recommendations made by Palomino in his treatise about the convenience of using slaked lime‐sand mortars according to traditional fresco recipes. Although lead‐based pigments were not traditionally recommended for frescoes because of their empirically known alterations when subjected to strong alkaline fresco medium, both Guillo and Palomino used them. Palomino, probably supported by his personal experience as a painter, recommended and used Naples yellow, which has been found in a good state of preservation. In contrast, white lead areas found on Guillo's paintings have transformed into lead oxides. Other pigments found in the vaulted ceiling such as smalt, goethite, haematite, azurite and malachite have also undergone substantial changes because of the extreme temperature conditions to which they were subjected in the church. Copyright © 2012 John Wiley & Sons, Ltd.     

The application of CARS for temperature measurements in high pressure combustion systems

The determination of accurate temperatures from CARS N₂ Q-branch spectra in premixed flames is discussed for pressures up to 40 bar. The influence of collisional line narrowing in the CARS spectra is modelled by a MEG fitting law. It takes into account collisions of N₂ with CO₂ and H₂O. The analysis of the CARS data showed that the non-resonant background has an increasing influence on temperature with increasing pressure. Little influence on the quality of the fit between theory and experiment was found. Since there is a danger of residual systematic temperature deviations, which cannot be identified from the quality of the fit, spontaneous rotational Raman scattering is employed as an independent measuring technique.