Precious coral non‐destructive characterization by Raman and XRF spectroscopy

Precious corals are some of the most valuable living marine resources, growing and commercially exploited only in limited areas of the world, namely the Mediterranean Sea and the Northern Pacific Ocean. Their skeleton is formed by calcium carbonate crystallized in the form of calcite whereas their color is because of the presence of partially demethylated polyene pigments. Recently, Pacific corals have been included in the appendix II of CITES list, while Mediterranean corals are still excluded. Different Corallium species of Corallidae family (e.g. Corallium rubrum, Corallium elatius and Corallium secundum) collected from different locations of the Mediterranean Sea and the Pacific Ocean were analyzed by Raman spectroscopy for the characterization of the reddish pigment and by X‐ray fluorescence (XRF) for the determination of the chemical composition of their skeletons, in order to obtain molecular and elemental data with two relatively easy and non‐destructive techniques, which can be used quite steadily for authentication purposes. Raman analysis demonstrated the presence of specific vibrational bands useful to identify the colored pigments as a mixture involving methylated and demethylated polyenes such as carotenoids and parrodienes, characterized by the presence of ―CH₃ groups along the polyene chain. The ratio between the Raman signal and fluorescence background was found to vary as a function of the macroscopic color of the coral, but Raman analyses resulted inadequate for distinguishing between corals having similar color but different origins. On the other side, XRF data provided reliable information for an appropriate separation between Pacific and Mediterranean corals at the elemental level. The results of this study will be of great relevance for the authentication and identification of the origin of corals in trade market by means of completely non‐destructive techniques. Copyright © 2016 John Wiley & Sons, Ltd.     

Shades of green in 15th century paintings: combined microanalysis of the materials using synchrotron radiation XRD, FTIR and XRF

A representative selection of green paintings from fifteenth century Catalonia and the Crown of Aragon are analyzed by a combination of synchrotron radiation microanalytical techniques including FTIR, XRD, and XRF. The green pigments themselves are found to be a mixture of copper acetates/basic copper acetates and basic copper chlorides. Nevertheless, a broader range of green shades were obtained by mixing the green pigment with yellow, white, and blue pigments and applied forming a sequence of micrometric layers. Besides the nature of the pigments themselves, degradation and reaction products, such as carboxylates, formates and oxalates were also identified. Some of the copper based compounds, such as the basic copper chloride, may be either part of the original pigment or a weathering product. The high resolution, high brilliance, and small footprint of synchrotron radiation proved to be essential for the analysis of those submillimetric paint layers made of a large variety of compounds heterogeneous in nature and distribution and present in extremely low concentrations.     

Analysis of confiscated fireworks using Raman spectroscopy assisted with SEM‐EDS and FTIR

A forensic analysis of several samples of pyrotechnic artefacts was performed by Raman spectroscopy assisted by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy (SEM‐EDS) and Fourier transform infrared (FTIR) analysis. Among the components, several nitrates, ammonium perchlorate, nitrocellulose, metallic titanium particles and shellac were detected. The combination of Raman spectroscopy and SEM‐EDS showed very useful performance. All components were detected by Raman spectroscopy except for shellac, kaolinite and titanium particles, which were not conclusive enough and had to be determined by FTIR and EDS. In contrast, many compounds were not detected by FTIR. Copyright © 2011 John Wiley & Sons, Ltd.     

Gilding and pigments of Renaissance marble of Abatellis Palace: non‐invasive investigation by XRF spectrometry

Most of the artworks constituting the collection of Renaissance statuary of Abatellis Palace in Palermo (Sicily) show evidence of colour layers and fragments of gold foil that probably once covered the whole marble surface. The restoration of some of these statues has allowed to carry out archaeometric studies about the painting technique and to highlight the original materials and inclusion present on the precious marbles by two famous Italian sculptors of the Renaissance, Francesco Laurana and Antonello Gagini. The measurements have been performed in situ through the integrated use of two non‐invasive techniques: visible fluorescence stimulated by ultraviolet light and X‐ray fluorescence. The ultraviolet‐induced fluorescence analysis has provided additional information on the conservation status of marble surfaces by differentiating the pictorial materials and highlighting the presence of gilding and pigment traces through their characteristic fluorescence response. The observation in ultraviolet light has been used as valuable guide for the identification of the significant points to be analysed by X‐ray fluorescence to characterise the original materials. X‐ray fluorescence measurements have cast light about their chemical composition and stratigraphical structure. Pictorial layers were identified: vermilion for red layers, blue pigment based on copper for blue layers and pure gold leaf for gilding layers. Principal component analysis of the data was capable of clustering the different painting materials, discriminating through their chemical content. The results represent an important scientific support both to the hypotheses about the original look of the artworks and to the resolution of restoration and conservation questions still open. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy,transmission electron microscopy,X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High‐resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)‐ and (100)‐oriented planes which stabilizes against further oxidation of the particles. X‐ray absorption spectroscopy (XANES) and X‐ray photoelectron spectroscopy (XPS) measurements at the O 1s‐edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO₂) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub‐oxide, +1 (Si₂O), +2 (SiO) and +3 (Si₂O₃), states are present. The analysis of the change in the sub‐oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.     

Quantitative non‐destructive determination of trace elements in archaeological pottery using a portable beam stability‐controlled XRF spectrometer

A portable beam stability‐controlled XRF spectrometer developed at the LNS/INFN laboratories at Catania (Italy) was used for the non‐destructive determination of some trace elements (Rb, Sr, Y, Zr and Nb) in fine pottery artefacts. The XRF system and the method developed to control the energy and intensity stability of the excitation beam are briefly discussed. Concentrations of Rb, Sr, Y, Zr and Nb were determined in 50 fine potsherds from the votive deposit of San Francesco in Catania by using a multi‐linear regression method. Additionally, in order to test the homogeneity of the material composing the fine pottery samples, a small portion of a few potsherds was powdered and analysed using the XRF system and the multilinear regression method. A comparison between non‐destructive and destructive approaches is presented and discussed. Finally, quantitative XRF data were compared with those obtained by chemical analysis of the powdered samples. The results allowed the testing of a non‐destructive methodology to be used for the identification and grouping of the different typological classes of fine pottery mainly represented in the San Francesco sanctuary. Copyright © 2005 John Wiley & Sons, Ltd.     

Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected pastels

Five French pastels and a sanguine drawing dating from the 17th to the 20th century were studied by Raman spectroscopy. Different operative conditions were used: the pastels were investigated through their protective glass, and the results obtained were compared with those obtained after removing the glass and after sampling a micrometric particle of pigment. Different parameters (wavelengths, powers of excitation and objectives) were tested in order to assess the optimal procedure of analysis for this fragile work of art. The results obtained for black (carbons), yellow (chrome/cobalt yellow), red (lead oxide, vermillion, orpiment), brown (red lead and chrome yellow), blue (Prussian blue, lapis lazuli/ultramarine), green (mixture of above blue and yellow pigments) and white (calcite, lead white, anatase) pigments are presented and the consistency of the pigments' period of use with the dating proposed for each pastel is evaluated. In one of the pastels, the blackening of the carnation colour made of an unstable mixture of lead white, red lead and vermilion was studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Non‐invasive probing of pharmaceutical capsules using transmission Raman spectroscopy

We demonstrate how transmission Raman geometry can be effectively used for non‐invasive probing of the content of pharmaceutical capsules. This approach is particularly beneficial in situations where the conventional Raman backscattering method is hampered or fails because of excessive surface Raman or fluorescence signals emanating from the capsule shell material, which pollute the much weaker subsurface Raman signals with undesired noise. It is demonstrated that such interfering signals can be effectively suppressed by the transmission geometry. The ability to avoid surface fluorescence and Raman signals in conjunction with the superior, bulk‐probing properties of the transmission Raman geometry provides an analytical technique ideally suited for fast on‐line process control monitoring applications in pharmaceutical industry where rapid, chemically specific bulk analysis is required. Copyright © 2007 John Wiley & Sons, Ltd.     

Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected miniature portraits

Six French miniature portraits on ivory and paper dating back to the 18th to 19th centuries have been studied by Raman spectroscopy. The miniatures have been investigated through their protective glass cover using different operating conditions: various laser wavelengths (1064, 785 and 532 nm), spectrometers (fixed and mobile) and objectives (10× to 200×). The results obtained for black (carbon), grey (carbon + chalk), red (lead oxide, vermillion), blue (Prussian or phthalocyanine blue), green (emerald or Paris green) and white (lead white) pigments are presented. The consistency of the period of use of the pigments with the proposed dating for each artwork is evaluated. Attention is paid to the analysis of the ivory substrates (assigned to Asian elephant ivory) and to the protective glass. Copyright © 2011 John Wiley & Sons, Ltd.     

Correction for the effect of soil moisture on in situ XRF analysis using low‐energy background

X‐ray fluorescence (XRF) analyses are affected by many matrix and geometrical factors that, generally, are possible to handle in laboratory conditions. However, when in situ analyses are considered, constraints in the measurement conditions make more difficult to handle some factors, such as moisture, affecting the measurement accuracy. Efforts have been made to correct some of the effects by inserting some steps in the sample preparation process. The problem is that each step added in this process, aiming a better precision and accuracy, makes the in situ measurement harder and longer to accomplish, influencing negatively the intrinsic advantages of the in situ measurement. In this work, we propose a method to correct the effect of soil moisture on in situ XRF analysis using low‐energy background. The method demands a simple calibration, after which a long drying procedure is not necessary before measuring the samples. Copyright © 2012 John Wiley & Sons, Ltd.     

A rapid,non‐destructive method of detecting diagenetic alteration in fossil bone using Raman spectroscopy

Biogenic isotopes of analytical interest may be stripped from bone during burial, reducing the utility of fossil specimens for paleobiological and paleoenvironmental reconstruction. Denudation of the bone lattice coupled with the addition of exotic ions can influence the Raman spectra of fossil bone. Modern bone samples (n = 43) were used to establish an unaltered bone standard, and a suite of synthetic apatite samples were produced to simulate the addition of various ions into the bone mineral lattice. Diagenetic alteration produces distinct spectral characters, providing qualifications for major ionic substitution, ionic heterogeneity, the abundance of structural carbonate, the presence of calcium carbonate and the presence of luminescent ions. Spectral indicators (proxies) provide the means of rapidly and nondestructively evaluating the degree of alteration and thus the analytical utility of fossil bones, potentially avoiding exhaustive and destructive analysis on finite material. Copyright © 2007 John Wiley & Sons, Ltd.     

Phthalocyanine identification in paintings by reflectance spectroscopy. A laboratory and in situ study

The importance of identifying pigments using non invasive (n.i.) analyses has gained increasing importance in the field of spectroscopy applied to art conservation and art studies. Among the large set of pigments synthesized and marketed during 20th century, surely phthalocyanine blue and green pigments occupy an important role in the field of painting (including restoration) and printing, thanks to their characteristics like brightness and fastness. This research focused on the most used phthalocyanine blue (PB15:1 and PB15:3) and green pigments (PG7), and on the possibility to identify these organic compounds using a methodology like reflectance spectroscopy in the UV, visible and near IR range (UV-vis-NIR RS), performed easily through portable instruments. Laboratory tests and three examples carried out on real paintings are discussed.     

Principal component analysis‐assisted energy dispersive X‐ray fluorescence spectroscopy for non‐invasive quality assurance characterization of complex matrix materials

The analytical challenges in direct quality assurance analysis of complex matrices (extreme matrix effects, spectral overlap, poor signal‐to‐noise ratio (SNR) for trace analytes, ‘dark matrix’, imprecise geometry, need for sample integrity) by energy dispersive X‐ray fluorescence (EDXRF) spectrometry necessitate development of novel techniques for material characterization. We demonstrate the utility of principal component analysis (PCA) in isotope‐excited EDXRF spectrometry of a complex matrix (in this case lubricating oil) in the context of a newly developed EDXRF and scattering (EDXRFS) technique. Lubricating oil quality may be interpreted in terms of its viscosity, anti‐wear, anti‐oxidation, and anti‐rust properties, which are detectable via B, Ca, Mg, Zn, Fe, Na additives (quality markers). Our method involves simultaneous non‐invasive acquisition of both fluorescence and scatter spectra from samples held in a propylene dish, and their modeling in a reduced multidimensional space for an interpretable overview that is analytically more useful than, and complementary to, fluorescence peak‐based quantitation of the additives; by this method, only Fe and Zn are directly detectable, but with SNR of the fluorescence peak 15–20 times poorer compared with analysis after sample digestion. Although Fe and Zn cannot distinguish the various lubricating oil brands, it can differentiate authentic from adulterated. The method was however found to be analytically useful when combined with PCA: various brands of lubricating oil were discriminated in addition to the detection of adulteration. PCA processing of the spectra showed that the most important quality assurance spectral signature information responsible for the success is contained in the scatter region (low‐Z elements). Evaluation of the performance of the method with respect to SNR (i.e. analysis time and therefore speed) showed that there was no significant difference in method performance of analysis live time in the range 100–1000 s, showing proof of concept for rapid characterization of complex matrix materials by PCA‐assisted EDXRFS. Copyright © 2012 John Wiley & Sons, Ltd.     

Non‐equilibrium polaritonics ‐ non‐linear effects and optical switching

This erratum refers to the article above, first published online on 31 December 2012 and later in print in Annalen der Physik, 525(1–2), 66–73 (2013).     

Raman scattering features of lead pyroantimonate compounds: implication for the non‐invasive identification of yellow pigments on ancient ceramics. Part II. In situ characterisation of Renaissance plates by portable micro‐Raman and XRF studies

The effectiveness of Raman spectroscopy (using a bench‐top system on standard pigments) for the characterisation of modified lead antimonate yellows was demonstrated in the already published Part I. The knowledge gained is employed here for the study of yellow glazes on genuine Renaissance plates with the aim of identifying non‐invasively lead pyroantimonate compounds by portable micro‐Raman equipment. The investigation was carried out directly on site, at the Victoria and Albert Museum (London, UK) and at the Museo Statale d'Arte Medievale di Arezzo (Arezzo, Italy), combining Raman and X‐ray fluorescence analyses. In addition to the spectral features of both unmodified Naples yellow and Sn‐ and Zn‐modified lead antimonate compounds, the Raman patterns related to partially modified pyrochlore structures were observed. For this reason, the possible Sn‐induced modification of Naples yellow by cassiterite (SnO₂), present within the glaze as opacifier was explored on lead antimonate yellow glaze mock‐ups fired at different temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

Subdiffraction‐limited chemical imaging of patterned phthalocyanine films using tip‐enhanced near‐field optical microscopy

A tip‐enhanced near‐field optical microscope, based on a shear‐force atomic force microscope with plasmonic tip coupled to an inverted, confocal optical microscope, has been constructed for nanoscale chemical (Raman) imaging of surfaces. The design and validation of the instrument, along with its application to near‐field Raman mapping of patterned organic thin films (coumarin‐6 and Cu(II) phthalocyanine), are described. Lateral resolution of the instrument is estimated at 50 nm (better than λ/10), which is roughly dictated by the size of the plasmonic tip apex. Additional observations, such as the distance scaling of Raman enhancement and the inelastic scattering background generated by the plasmonic tip, are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

In situ monitoring of solid‐state transition of p‐aminobenzoic acid polymorphs using Raman spectroscopy

The purpose of this study is to investigate the mechanism of solid‐state polymorphic transition of p‐aminobenzoic acid (PABA) using in situ Raman spectroscopy measurement. The polymorphic transition experiments were conducted on a micro quartz vessel mounted on a microscope, hot and cold stage, under isothermal conditions. The temperature was precisely controlled by a standalone temperature controller equipped with liquid nitrogen cooling system. The Raman spectroscopy probe was positioned on the surface of the solid sample in the micro vessel. The polymorphic transition progression was in situ monitored and recorded by Raman spectroscopy. Based on the polymorphic transition rate resulted from the quantitative analysis of Raman spectra, the mechanism of solid‐state polymorphic transition of PABA was examined by various empirical kinetic models. An Arrhenius analysis was also performed to calculate activation energies from 134.7 kJ mol⁻¹ to 137.7 kJ mol⁻¹ for the transition. The results demonstrated that in situ Raman spectroscopy is a valuable and accurate technique to probe polymorphic transition process. Copyright © 2009 John Wiley & Sons, Ltd.     

Reflection-scanning near-field optical microscopy and spectroscopy of opaque samples

Opaque samples are imaged by Scanning Nearfield Optical Microscopy (SNOM) in reflection mode: A quartz glass fiber tip is used both to illuminate the sample and to collect light locally reflected from or emitted by the surface. The collected light is coupled out by a 2×2 fiber coupler and fed into a grating spectrometer for spectral analysis at each sampled point. The tip-sample distance is controlled by a shear-force feedback system. The simultaneous measurement of topography and optical signals allows an assessment of imaging artifacts, notably topography-induced intensity changes. It is demonstrated that an optical reflectance contrast not induced by topographic interference can be found on suitable samples. Local spectral analysis is shown in images of a photoluminescent layer.