An example of the complementarity of laser‐induced breakdown spectroscopy and Raman microscopy for wall painting pigments analysis

Abstract

Laser-induced breakdown spectroscopy (LIBS) and Raman microscopy were used for the identification of pigments in wall painting. Raman spectroscopy, which provides the molecular 'fingerprint' of the compound, is nowadays widely used by the archaeometry community, especially for pigment analysis. LIBS, which provides the elementary composition of samples, is a rapid noncontact method, enabling layer-by-layer analysis through a precise laser ablation of the sample. This work deals with the behavior of pigments after a LIBS analysis, by trying to identify the compounds before and after the laser shot. Six commercial pigments prepared with the fresco technique were investigated: ultramarine blue, red lead, charcoal, a yellow and a red ochre, and a green earth. Raman spectra, acquired on the sample surface and in the crater induced by LIBS analysis, were compared. The results show that these pigments are well recognized after a LIBS measurement. The analysis of green earth illustrates that the combination of these two techniques gives complete information from a sample.

A multi-technique approach, based on mobile/portable laser instruments, for the in situ pigment characterization of stone sculptures on the island of Crete dating from Venetian and Ottoman period

“…Complementary analysis is performed by LIBS, which typically affords strong emission signals that enable one to draw information on the elemental composition of the paint, mainly the inorganic component of it, based on the characteristic atomic emission lines recorded in the spectra [25,26]. A single pulse is adequate for obtaining a spectrum with high signal-to-noise ratio (S/N).…”

“…Such an approach can lead to improved Raman data if, for example, superficial dust and/or fluorescent impurities have been removed during laser ablation. Additionally this approach may provide extra information by permitting Raman analysis to probe underlying paint layers [25]. This procedure was followed, in several cases throughout the studies reported herein, particularly when strong fluorescence was detected interfering with Raman analysis.…”

“…Particularly, in the context of wall painting analysis, research studies by Bruder et al [25] illustrate the complementarity of LIBS and Raman microscopy for the in situ analysis of fresco replicas while Westlake et al [26] have demonstrated the combined use of the techniques in the analysis of mural painting fragments, still performing analyses on small plaster fragments in the analytical laboratory. At this stage it is noted that hybrid LIBS-Raman systems, in which the two spectroscopic techniques utilize the same pulsed laser source, spectrometer and detector, have been proposed that perform combined measurements on heritage samples.…”

Analysis of natural and artificial ultramarine blue pigments using laser induced breakdown and pulsed Raman spectroscopy, statistical analysis and light microscopy

“…Ultramarine was originally used to distinguish the blue pigment lapis lazuli (extracted from the mineral lazurite (approximate formula (Na, Ca) 8 (AlSiO 4 ) 6 (SO 4 , S, Cl) 2 ) and imported from Asia) from other less expensive blue pigments, in particular the blue copper mineral pigment azurite (Cu 3 (CO 3 ) 2 (OH) 2 ) [1]. In the past the principal source of the mineral and pigment was in ancient quarries of Badakshan (now Afghanistan).…”

“…Raman spectroscopy has often been used for the molecular analysis and the characterization of inorganic pigments from works of art [8,9], with a variety of databases available for ancient and modern pigments [10][11][12]. A wide range of artistic and historical materials have been studied by using this non-destructive, and in some cases non-invasive [13,14], spectroscopic technique.…”