Influence of ns-laser wavelength in laser-induced breakdown spectroscopy for discrimination of painting techniques

Abstract

The influence of ns-laser wavelength to discriminate ancient painting techniques such as are fresco, casein, animal glue, egg yolk and oil was investigated in this work.This study was carried out with a single shot laser on samples covered by a layer made of a mixture of the cinnabar pigment and different binders. Three wavelengths based on Nd: YAG laser were investigated (1064, 532 and 266 nm). The plasma is controlled at the same electron temperature after an adjustment of pulse energy for these three wavelengths on a fresco sample without organic binder. This approach allows to eliminate the effects of laser pulse energy and the material laser absorption.Afterwards, the emission spectra were compared to separate different techniques. The organic binding media has been separated based on the relative emission intensity of the present CN or C 2 rovibrational emissions. In order to test the capability of separating or identifying, the chemometric approach (PCA) was applied to the different matrix. The different solutions in term of wavelength range to optimise the identification was investigated. We focused on the evaluation for the laser wavelength to insure a better separation. The different capacity was interpreted by differentiating 1 Corresponding author. E-mail address: vincent.detalle@culture.gouv.fr the binders by the altered interaction mechanisms between the laser photon and the binders. Also, the electron temperature in the plasma was estimated, which provided the evidences to our findings.

Analysis of heritage stones and model wall paintings by pulsed laser excitation of Raman, laser-induced fluorescence and laser-induced breakdown spectroscopy signals with a hybrid system

“…Also for binder 2, the main broad band is shifted to longer wavelengths (maximum at 455 nm), in relation with the maximum of the fresco sample, probably due to the presence of egg yolk [3,35,36]. LIB spectra of the model wall paintings were recorded on the paint and mortar sides of the substrate by irradiation at 266 nm, a wavelength which has been found optimum for LIBS analysis of this type of samples [21]. All these spectra were obtained with the diffraction grating of 1200 lines mm -1 .…”

“…LIBS has been used in a wide variety of analytical applications for the qualitative, semiquantitative and quantitative analysis of materials and offers specific features of particular relevance in the context of analysis of cultural heritage materials [1,2,[10][11][12]. A recent work has showed the effect of irradiation wavelength on the analysis by LIBS of painting samples, concluding that short wavelengths favour the characterization of this kind of substrates [21].…”

Applications of laser-induced breakdown spectroscopy in cultural heritage and archaeology: a critical review

“…Generally, these studies demonstrate that LIBS can be successfully used to identify inorganic, but also organic materials such as the protective polymer or binders [73]. Comparing the emission of CN and C 2 bands in the plasma, in fact, Bai et al [74] discriminated casein, animal glue, oil and egg yolk in mock-up samples painted with a layer of the pigment cinnabar (HgS). To advance the separation, chemometric method based on the Principal Component Analysis (PCA) was used; the 266 nm radiation allowed for a better performance.…”

The first evaluation of diagenesis rate of ancient bones by laser-induced breakdown spectroscopy in archaeological context prior to radiocarbon dating

“…LIBS especially offers an analytical ability for light elements identification and molecular band emission in the organic materials such as animal products, polymers, the products for heritage conservation like the mural painting (binder, adhesives, and consolidation products), etc. [17][18][19][20]. This work focuses on technical feasibility for the preliminary analysis before preforming radiocarbon dating for bone samples.…”