Laser Ablation-Inductively Coupled Plasma Mass Spectrometry for the Characterization of Pigments in Prehistoric Rock Art

Abstract

In this work, several red-colored paintings of post-Paleolithic schematic style found in 10 different shelters in the vicinity of the Vero River (Huesca) were sampled and subjected to analysis by means of scanning electron microscopy-energy-dispersive X-ray spectrometry (SEM-EDX), Raman spectroscopy, and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS). The goal of this research was to obtain meaningful information on the samples composition, in order to establish differences or similarities among them. The combined use of these techniques proved beneficial, as Raman data permitted structural information on the compounds present (hematite was identified as the main pigment, whereas calcite and gypsum are the main components of the substrate layer, as well as of the accretions that covered the pigments) to be obtained, while the quantitative values obtained by SEM were suitable for the use of Ca as internal reference during LA-ICPMS analysis. However, it was this latter technique that provided the most relevant data for fingerprinting purposes. The potential of this technique for obtaining spatially resolved information allowed the multielement quantitative analysis of the pigment layer, in spite of the presence of superficial accretions. The sensitivity of the technique permitted the determination of more than 40 elements present in a wide concentration range (from microgram per gram to 10% level) with minimum sample consumption (approximately 900 ng for each sample, corresponding to five replicates). Finally, in order to establish significant differences, only those elements showing a high correlation with Fe (As, Co, Mo, Sb, Tl, and Zr, in this case) were selected, as it is expected that these were truly present in the original pigment, while others could have migrated into the pigment layer throughout time. By using this information, it seems feasible to discriminate between various paint pots, as demonstrated for the samples under investigation.At the end of the Ice Age, the great herds that had provided sustenance for the Paleolithic hunters disappeared from France and Spain. In the large forest areas that flourished owing to the warmer climate, groups of deer and related species lived. These animals were fast and elusive and, thus, much harder to hunt. As a consequence, man had to modify his hunting techniques, as well as forage for the seeds and fruits that the forest provided or the fish that were available in rivers or on the coast. Cooperation was essential, and this change was reflected in the art of this postPaleolithic period. 1 Bands of such hunter-gatherers left a record of their activities in shelters scattered throughout the Iberian Peninsula, among other regions. The differences with Paleolithic paintings are evident, as a simpler silhouette technique emerges. Moreover, the new paintings seem to have a clear narrative meaning, featuring a higher proportion of hominine figures. 2 Investigation of these paintings can provide relevant hints about the technological level as ...

An approximation to the study of black pigments in Cova Remigia (Castellón, Spain). Technical and cultural assessments of the use of carbon-based black pigments in Spanish Levantine Rock Art

“…Iron oxides (haematite) have so far been identified as the basic raw material for red pigments in the Valltorta-Gasulla area; these findings agree with those obtained in other Levantine regions Resano et al, 2007;Alloza et al, 2009;Hernanz et al, 2010). The presence/absence of impurities or trace elements in these red pigments points to the use of different raw materials.…”

“…The structure of Levantine paintings in Cova Remigia can be described from a stratigraphic model that distinguishes three main layers whose thickness and composition play an important role in assessing the results of the EDXRF analyses: a) the limestone bedrock surface over which the pigments are applied, mainly composed by calcium carbonates, calcium sulphates and iron oxides, is considered as a material of infinite thickness from the point of view of the XRF radiation; b) a paint layer with a thickness of a few microns applied over the rock (Resano et al, 2007); and c) a surface patina that covers the motif itself, produced by the action of microorganisms or by the interaction between the wall and the environment. These patinas are mainly composed of oxalates, calcium carbonates or calcium sulphates, and their thickness reaches up to few tens of microns Resano et al, 2007;Hernanz et al, 2010).…”

“…These patinas are mainly composed of oxalates, calcium carbonates or calcium sulphates, and their thickness reaches up to few tens of microns Resano et al, 2007;Hernanz et al, 2010). The penetration depth of the XRF radiation into the surface patina, assuming a composition similar to oxalates (CaC 2 O 4 ) and a density of 2.2 g/cm 3 , irradiated with a continuum Xray spectra of 30 kV with a maximum of 20 keV giving rise to 50% of fluorescence radiation, is about 700 mm.…”

Role of laser ablation–inductively coupled plasma–mass spectrometry in cultural heritage research: A review

“…Human In the case of pigments analysis, LOD values lay in the ranges 10-100 ng g −1 for atomic masses higher than 80 amu and 100-1000 ng g −1 for the ones lower than 80 amu (Resano et al [115]). For copper-based objects, LOD values were less than 1 ng g −1 (ppb) in Dussubieux et al [104].…”

“…Rubidium was the key element able to separate the sources. LA-ICP-MS proved to be very effective also for the investigation of prehistoric paintings [115]. Samples of hematite from shelter paintings in the surroundings of Vero River (Huesca) were analyzed by SEM-EDX and Raman spectroscopy in order to verify differences among the archaeological sites, but only the results of LA-ICP-MS analyses were relevant in identifying As, Co, Mo, Sb, Tl and Zr as discriminating key elements.…”