Iacopo Osticioli

Spectroscopic analysis of works of art using a single LIBS and pulsed Raman setup

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.

Shift-excitation Raman difference spectroscopy-difference deconvolution method for the luminescence background rejection from Raman spectra of solid samples.

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.

An Optimization of Parameters for Application of a Laser-Induced Breakdown Spectroscopy Microprobe for the Analysis of Works of Art

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 μm) 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.

Assessment of the ageing of triterpenoid paint varnishes using fluorescence, Raman and FTIR spectroscopy

AbstractThe 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. FigureExcitation emission spectra of films triterpenoid varnishes mastic and dammar have been recorded as a function of ageing. Using multivariate statistical analysis, dedrograms of contours of fluorescene excitation emission spectra are used to assess the differences in spectra of dammar and mastic

A remote scanning Raman spectrometer for in situ measurements of works of art

In conservation science, one of the main concerns is to extract information from an artistic surface without damaging it. Raman spectroscopy has emerged in recent years as a reliable tool for the non-destructive analysis of a wide range of inorganic and organic materials in works of art and archaeological objects. Nevertheless, the technique is still mainly limited to the analysis of micro-samples taken from artistic surfaces. The development of an instrument able to perform non-contact analysis of an area of a few square centimeters aims to further increase the employment of this technique. This paper describes the development of a prototype Raman scanning spectrometer based on a diode laser, a 2D scanning mirror stage and a custom optical system, which can map a surface of 6 cm in diameter at a working distance of 20 cm. The device exhibits collecting optics with a depth of field close to 6 cm, which makes the Raman system suitable for the analysis of non-flat surfaces and three-dimensional objects. In addition, the overall dimensions and weight of the instrument have been limited in order to make the device transportable and, in principle, usable for in situ measurements. Details on the design of the device, with particular emphasis on the collecting optical system, and on results of the characterization tests carried out to assess its performances are reported. Finally, an example of an application involving the identification of pigments from a model painting is presented.

A new compact instrument for Raman, laser-induced breakdown, and laser-induced fluorescence spectroscopy of works of art and their constituent materials.

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.

Potential role of LIPS elemental depth profiling in authentication studies of unglazed earthenware artifacts

We focused on the behaviour of elemental distributions in unglazed earthenware artifacts. The potential role of the elemental depth profiles, as measured using a portable laser induced plasma spectroscopy (LIPS) device, in discriminating between genuine unearthed archaeological findings and modern counterfeits was investigated. Measurements were carried out on a set of ancient unglazed earthenware samples from archaeological excavation and on some corresponding modern artifacts. The analyses pointed out that the elements exhibiting the most significant and repeatable modulations were iron and calcium. A systematic depletion of the former was observed in all the samples analysed, without any possibility of discrimination, whereas calcium had different behaviours. A recurrent presence of high-amplitude, broad, and structured calcium content peaks in proximity of the surface of genuine unearthed samples was measured, a feature that was not observed for modern artifacts. This result provides the first evidence of the possible use of calcium depth distribution measured using LIPS analysis as a marker in authentication studies of unglazed earthenware artifacts.

Combined neutron and laser techniques for technological and compositional investigations of hollow bronze figurines

Here, an innovative non-invasive multi-analytical approach for the archaeometallurgical characterisation of ancient bronze artefacts using high resolution neutron tomography, time of flight neutron diffraction, and laser induced plasma spectroscopy has been investigated. We show its effectiveness through an example application aimed at describing the crafting processes, characterising the alloy compositions and deterioration phenomenologies of three small bronze figurines from the antiquarian collection of the Egyptian Museum of Florence. The present methodology has allowed unprecedented overall archaeometallurgical descriptions of these artefacts based on the detection of fine morphological details, degree of mineralisation, elemental and phase composition of the metal walls, and mineral contents of the core materials. Such an approach can be extended to other hollow copper alloy artefacts in order to identify their raw materials and interpret their technological processes.

Non-destructive characterisation of fourteenth century painting by means of molecular spectroscopy and unilateral NMR

Abstract The present work was aimed at characterising the materials and assessing the state of conservation of the ‘Adorazione dei Magi’, a wooden panel painted by Bartolo di Fredi in the second half of fourteenth century. To this goal, innovative non-destructive investigation techniques such as portable Raman spectroscopy, visible reflectance spectroscopy and unilateral nuclear magnetic resonance, were used in situ in order to achieve surface and bulk compositional data. The former allowed the identification of the artist’s palette including cinnabar, red ochre, minium, carbon black, lead white, ultramarine blue, malachite and phthalocyanine green, while the latter provided information on the stratigraphic structure and state of conservation of the wooden panel.

Preliminary investigation of combined laser and microwave treatment for stone biodeterioration

Abstract In this work, the potential applications of surface laser removal of biological crusts from Carrara marble artefacts and in-depth microwave selective heating for treatment of possible endolithic growths have been evaluated. The investigations were carried out on seriously deteriorated marble fragments from the monumental tombs of the English Cemetery in Florence, Italy. The second harmonic (532 nm) of a Q-switched Nd:YAG laser was used for cleaning while a microwave system emitting at 2.45 GHz was tested for in-depth sterilization. As is well known, microwaves are strongly absorbed by water via dipolar energy dissipation, which permits selective heating of endolithic organisms. The effects of laser and microwave treatments were characterized using scanning electron microscopy (SEM) along with chlorophyll fluorescence with pulsed amplitude modulated imaging. The latter has allowed the quantification of the impairment effects to photosystem II of epilithic phototrophic organism residues by mapping the maximum quantum yield, while the damage to endolithic growths was evaluated by means of SEM following osmium tetroxide staining of cytoplasmic lipids. The results provide an early picture of the development and application perspectives of the combined laser and microwave treatments in the conservation of biodeteriorated stone artefacts.