Abstract: A small, potentially transportable prototype instrument capable of carrying out Raman, laser-induced breakdown (LIB), and laser-induced fluorescence (LIF) spectroscopy using a single pulsed laser source was developed for the analysis of cultural heritage objects. The purpose of this instrumentation is to perform fast and reliable analysis of surfaces with minimum damage to an object. For this purpose, a compact (51 x 203 x 76 mm) nanosecond Q-switched neodymium doped yttrium aluminum garnet laser (8 ns, 20 Hz, 0.01-115 mJ/pulse) was used as an irradiation source. The use of a nanosecond-gated detector sensitive between 180 and 900 nm allows the acquisition of elemental emissions in LIB spectroscopy and can also be employed for both LIF and time-resolved Raman spectroscopy. In this work, attention is focused on the description of the instrument and its optical components, and two examples of applications for the analysis of pigments and binding media used in works of art are presented.
Abstract: The assessment of the influence of natural and artificial ageing on the spectrofluorescence of triterpenoid varnishes dammar and mastic is the focus of this work. Both Fourier transform infrared (FTIR) microscopy using attenuated total reflectance and Raman spectroscopy have been employed for complementary molecular analysis of samples. Synchronous fluorescence spectroscopy, excitation emission spectroscopy, and statistical analysis of data have been used to monitor changes in the optical properties of varnish samples. Assessment of naturally and artificially aged samples using excitation emission spectroscopy suggests that extensive exposure to visible light does not lead to easily appreciable differences in the fluorescence of mastic and dammar; cluster analysis has been used to assess changes, which occur with artificial ageing under visible light, indicating that differences in the fluorescence spectra of aged triterpenoids may be insufficient for their discrimination. The results highlight significant differences between the initial fluorescence of films of dammar and mastic and the fluorescence, which develops with ageing and oxidation, and specific markers, which change with ageing in FTIR and Raman spectra, have been identified.
Abstract: The present study considers the use of a nanosecond pulsed laser setup capable of performing laser induced breakdown spectroscopy (LIBS) and pulsed Raman spectroscopy for the study of multilayered objects in the field of cultural heritage. Controlled etching using the 4th harmonic 266 nm emission of a Nd:YAG laser source with a 8 ns pulse duration was performed on organic films and mineral strata meant to simulate different sequence of layers usually found in art objects such as in easel and mural paintings. The process of micro ablation coupled with powerful spectroscopic techniques operating with the same laser source, constitutes an interesting alternative to mechanical sampling especially when dealing with artworks such as ceramics and metal works which are problematic due to their hardness and brittleness. Another case is that of valuable pieces where sampling is not an option and the materials to analyse lie behind the surface. The capabilities and limitations of such instrumentation were assessed through several tests in order to characterize the trend of the laser ablation on different materials. Monitored ablation was performed on commercial sheets of polyethylene terephthalate (PET), a standard material of known thickness and mechanical stability, and rabbit glue, an adhesive often used in works of art. Measurements were finally carried out on a specimen with a stratigraphy similar to those found in real mural paintings. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: Pulsed laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy were performed using a novel laboratory setup employing the same Nd:YAG laser emission at 532 nm for the analysis of five commercially available pigments collectively known as "ultramarine blue", a sodium silicate material of either mineral origin or an artificially produced glass. LIBS and Raman spectroscopy have provided information regarding the elemental and molecular composition of the samples; additionally, an analytical protocol for the differentiation between natural (lapis lazuli) and artificial ultramarine blue pigments is proposed. In particular LIBS analysis has allowed the discrimination between pigments on the basis of peaks ascribed to calcium. The presence of calcite in the natural blue pigments has been confirmed following Raman spectroscopy in specific areas of the samples, and micro-Raman and optical microscopy have further corroborated the presence of calcite inclusions in the samples of natural origin. Finally multivariate analysis of Laser induced breakdown spectra using principal component analysis (PCA) further enhanced the differentiation between natural and artificial ultramarine blue pigments.
Abstract: A nanosecond pulsed laser setup has been optimized to perform laser-induced breakdown spectroscopy (LIBS) and pulsed Raman spectroscopy measurements in the field of cultural heritage. Three different samples of artistic/architectural interest with different typologies have been analyzed. The results from the two techniques allowed the identification of the materials used in their manufacture or contaminating them, probably coming from atmospheric pollution and biological activity. No sampling and sample preparation was required before the measurements, and no visual or structural damage was observed. Depth profiling using LIBS was performed in one of the samples, providing elemental information along the different layers composing the object and covering its surface. The quality of the results and the rather short time needed for the measurements and for switching between techniques confirmed the instrument's capabilities and specificity for dealing with objects of artistic or historical interest.
Abstract: The analysis of protein-based paint media used in paintings is presented using micro-Raman spectroscopy, carried out with a diode laser emitting at a wavelength of 785 nm. Following a contextualisation of the analysis and ageing of protein-based binding media, a consideration of the effects of artificial ageing using visible light on the Raman spectra of binding media is given and the interpretation of changes to the Raman spectra of selected binding media is presented. Bands associated with aromatic amino acids are most affected by ageing, but spectra retain diagnostic information for the identification of proteins. Specific changes to the spectra of dairy and collagen-based binding media are described and explained with reference to the oxidation of amino acids. A multivariate approach using Principal Component Analysis has been chosen for the assessment of the bands in C-H stretching region for which a large set of over 150 spectra were recorded from artificially and naturally aged binding media which included egg white, egg yolk, milk and casein, and collagen-based glues from rabbit skin, ox bone, parchment and sturgeon bladder. Raman spectroscopy has been used for an assessment of the effects of ageing and the detection of degradation due to exposure of light. Multivariate analysis has allowed the differentiation between a large data set of spectra of naturally and artificially aged binding media. Copyright (c) 2008 John Wiley & Sons, Ltd.
Abstract: Laser-induced breakdown spectroscopy (LIBS) provides many advantages for analysis of works of art. Both qualitative and semi-quantitative information about the elemental composition of an object can be rapidly obtained using LIBS. The time of response is on the order of a few seconds and no sample preparation is required. The possibility of performing analysis in museums and archeological sites makes LIBS particularly important; the combination of laser ablation and analysis as encountered in LIBS provides means to effectively carry out depth profiling of samples. By combining the use of a microscope, the dimension of the spot of the laser used to carry out analysis can be reduced and the spatial resolution highly improved; in this way, a very small area of the sample (on the order of 10 miccrom) can be analyzed. The aim of this work is to investigate the best working conditions in order to obtain the least amount of material removal during analysis, and, at the same time, the best quality in the spectral response for rapid and reliable identification of the elemental composition of an object. First, investigations were undertaken using metal alloys; second, the optimized LIBS conditions were used for analysis of models of painting layers prepared in the laboratory. Finally, a painting cross-section and a 19th century painted icon were analyzed using the micro-LIBS setup.
Abstract: Analysis of paint samples from a 16th C. wall painting in the church of Agios Sozomenos in Galata, Cyprus resulted in the identification of a copper-based, pigment degradation product - a hydrated copper oxalate, analogous to the naturally occurring blue-green mineral Moolooite. The identification of copper oxalate, a deterioration (alteration) product more often associated with the deterioration of bronze was possible through the integrated use of both micro-FTIR in reflectance for spot analysis of areas on the surface of an embedded cross-section, and FTIR reflectance imaging for the localisation of the presence of copper and calcium oxalates within the stratigraphy of the painting. Further, micro-Raman spectroscopy was employed for the analysis of unembedded fragments of the painting, confirming the presence of both copper oxalate and calcium oxalate. Finally, novel methods for the removal of salt interferences were employed for analysis using Gas Chromatography-Mass Spectrometry (GC-MS), which revealed the presence of both oxalate and phosphate ions and, following multivariate analysis of the amino acid profile, identified casein as the binder of the paintings. The imaging of calcium oxalates within the stratigraphy of wall painting samples is important and significant not only for the study of copper-based pigments in general, but especially for the analysis of pigments used for painting on exterior surfaces. (C) 2008 Elsevier Masson SAS. All rights reserved.
Abstract: in this work, non-destructive techniques were employed for the spectrofluorimetric and micro-Raman differentiation of solid films of egg yolk and egg white as a function of exposure to light. Using both techniques it is possible to discriminate between the samples on the basis of composition and follow some chemical changes involved during the light-ageing of egg proteins and fatty acid esters. In egg white, fluorescence emission spectra highlighted the presence of multiple fluorophores, with an effective broadening of the fluorescence emissions following light exposure, ascribed to the partial oxidation and depletion of tryptophan; in the Raman spectrum of dark-aged egg white a peak at 758 cm(-1) is ascribed to the vibrational mode of tryptophan, which is completely absent in the spectrum of samples exposed to light. Changes in the fluorescence of egg yolk following exposure to light are ascribed to the degradation of amino acids, cross-linking between amino acids and the formation of oxygenated triacylglycerides. These results are corroborated with Raman spectra of the light-exposed samples, which are associated with wavenumber shifts with respect to the dark-aged sample for the Amide I and for the characteristic carbonyl vibration at 1744 cm(-1) ascribed to the oxidation of fatty acid esters. Copyright (C) 2008 John Wiley & Sons, Ltd.
Abstract: The feasibility of the shift-excitation Raman difference spectroscopy-difference deconvolution (SERDS-DDM) method for fluorescence suppression from Raman spectra of solid samples is discussed. For SERDS measurements a tunable diode laser source with an emission band centered at 684 nm is coupled to a conventional micro-Raman apparatus and a monochromator device is used for checking the excitation frequency stability. The shifted Raman spectra are then mathematically treated and a deconvolution procedure is used to reconstruct the Raman spectrum devoid of fluorescence. Two different cases are presented. In the first one, fluorescence is intrinsic to the sample and the Raman spectrum of cinnabar pigment is finally reconstructed. In the second, the presence of an external luminescence background in the spectrum of a pure sulfur crystal is considered. The SERDS-DDM reconstructed spectra are compared with spectra obtained via multi-point baseline subtraction and a significant improvement in the detection of weak bands is demonstrated. Practical insights for the application of this method are presented as well.
Abstract: This work presents Raman spectra obtained from thin films of protein materials which are commonly used as binding media in painted works of art. Spectra were recorded over the spectral range of 3250-250 cm(-1), using an excitation wavelength of 785 nm, and several bands have been identified in the fingerprint region that correspond to the various proteins examined. Differences in the C-H vibrations located between 3200 and 2700 cm(-1) can be accounted for with reference to the amino acid composition of the protein-based binding media as well as the presence of fatty acid esters, in the case of egg yolk. In addition, the discrimination of different proteins on the basis of variations in spectra between 3200 and 2700 cm(-1) can be achieved following multivariate analysis of a large data set of spectra, providing a novel and nondestructive alternative based on Raman spectroscopy to other methods commonly used for the analysis of proteins.
Abstract: A novel setup, combining two spectroscopic techniques, laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy in a hybrid unit, is described. The work presented herein is part of a broader project that aims to demonstrate the applicability of the hybrid LIBS-Raman unit as an analytical tool for the investigation of samples and objects of cultural heritage. The system utilizes a nanosecond pulsed Nd:YAG laser (532 nm) for both LIBS and Raman analysis. In the Raman mode, a low intensity beam from the laser probes the sample surface and the scattering signal is collected into a grating spectrograph coupled to an intensified charge-coupled device (ICCD) detector, which records the Raman spectrum. In the LIBS mode a single high intensity pulse from the laser irradiates the sample surface and the time- and spectrally-resolved emission from the resulting laser ablation plume yields the LIBS spectrum. The use of a non-gated CCD detector was found to produce similar quality data (in terms of S/N ratio and fluorescence background) in the Raman mode, while in the LIBS mode spectral features were clearly broader but did not prevent identification of prominent atomic emission lines. Several model pigment samples were examined and the data obtained show the ability of the hybrid unit to record both Raman and LIBS spectra from the same point on the sample, a clear advantage over the use of different analytical setups.
Notes: cited By (since 1996) 0; Conference of International Conference on Heritage, Weathering and Conservation, HWC 2006; Conference Date: 21 June 2006 through 24 June 2006; Conference Code: 75464
Abstract: SERDS (shift excitation difference spectroscopy) and SSRS (subtracted shifted Raman spectroscopy) methods were applied for fluorescence-background rejection in the Raman spectra of colored materials. These techniques are based on the assumption that the fluorescence contribution can be completely eliminated by subtracting two Raman spectra acquired at two shifted laser excitation frequencies. For the SERDS method a micro-Raman experimental apparatus coupled with a tunable diode laser (central emission at 684 nm) was set up. SSRS measurements were made on a commercial micro-Raman instrument; in this case the shifted spectrum was obtained by moving the spectrometer grating. Raman spectra were then reconstructed by applying the difference deconvolution method that automatically converts the difference signals in Raman peaks through a deconvolution operation. These techniques were tested on two reference colors (ultramarine and 6,6'-dibromoindigotine) and two colored samples of unknown composition (a Pompeian pink powder and a blue paint from a XVII century painting). Fluorescence-background subtraction and the following operation of spectra reconstruction took place successfully with no errors in Raman peaks, width and wavenumber position. In addition, even weak spectral details were revealed favoring the comparison with reference data for a molecular identification. Copyright (C) 2006 John Wiley & Sons, Ltd.
