Methodological Approach (In Situ and Laboratory) for the Characterisation of Late Prehistoric Rock Paintings—Penedo Gordo (NW Spain)

Beatriz Comendador Rey,Jose Santiago Pozo-Antonio,Pablo Barreiro,Lara Alves Bacelar

doi:10.3390/min11060551

Beatriz Comendador Rey, Jose Santiago Pozo-Antonio + Show 2 more

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https://doi.org/10.3390/min11060551

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Journal: Minerals	Publication Date: May 22, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: Universidade de Vigo, University of Coimbra

Abstract

This paper draws on the study of the prehistoric art site of Penedo Gordo (NW Spain) resulting from a collaborative interdisciplinary research. One of its primary goals was to design and put into practice a multi-analytical protocol for characterising prehistoric rock paintings, combining in situ and laboratory analytical techniques. Thus, following the archaeological assessment of the site, the panels exhibiting red paintings were analysed by colour spectrophotometry and portable Raman spectroscopy. Analytical techniques were applied to a collection of samples exhumed from the excavation that simultaneously took place on site. These included three red accretions on different substrates (compact soil, white quartzite and grey quartzite) and stone fragments representative of the outcrop’s petrographic variability, aiming to determine their mineralogical composition, texture and study the stone-paint boundaries. Moreover, colouring materials exhumed from the excavation and collected in the immediate surroundings of the rock outcrop were analysed in order to scrutinise the provenience rock art’s raw materials. Laboratory analysis consisted of stereomicroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. One of the major outcomes was the discovery of a drop of red pigment preserved in an archaeological layer associated with Late Neolithic/Copper Age material remains.

Highlights

Penedo Gordo is a Late Prehistoric rock art site that was recently discovered in southeastern Galicia (Spain)
The panel shows, on the lefthand side, dots and bars typical of the Schematic Art tradition and on the right, remains of paintings forming a group of lines barely visible to the naked eye and that were only able to be recorded by enhanced digital photography
This paper details the physical, chemical and mineralogical characterisation of the motifs at Penedo Gordo (NW Spain); two panels in the northern area and three panels in the western area were documented in situ with different techniques of digital photographic enhancement, colour spectrophotometry and Raman spectroscopy

Summary

Introduction

Penedo Gordo is a Late Prehistoric rock art site that was recently discovered in southeastern Galicia (Spain). The recipes of prehistoric paintings most frequently include inorganic substances, mainly red-orange and black pigments that might have been mixed with organic binders of vegetable or animal origin [3,4,5,6]. In Iberia, black pigments were mainly produced from charcoal or soot and red pigments were composed of hematite (Fe2O3) or red ochre [6]. The latter is a natural earth in which iron oxides and hydroxides are mixed with clay and with minerals such as quartz (SiO2), dolomite (CaMg(CO3)2), hydromagnesite (Mg5(CO3)4(OH)2·4H2O), calcite (CaCO3), aragonite (CaCO3), gypsum (CaSO4·2H2O), muscovite (KAl2(AlSi3O10)(OH)2), feldspar ((K, Na, Ca, Ba, NH4)(Si, Al)4O8), etc. The Fe content is lower than the clay content even at concentrations below 1%, the colour obtained is red [8,9]

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