Looking for Painting Mixtures to Glimpse Pictorial Techniques: A Micro-Stratigraphic Physicochemical Approach to the Rock Art From the Oyola’s Caves (Argentina)

Abstract

Could not be possible that rock paintings with similar hues and morphologies were the results of different painting events inside a cave but distanced in time? Is there any archaeometric approach that allows us to evidence these subtle differences? Aiming to address these inquires, in this work are presented the potentials of new physicochemical lines of evidence for characterization and differentiation of painting mixtures. This will improve the understanding of the technical heterogeneity and temporal complexity of painting sets executed in a particular archaeological site. In order to explore these points, the results obtained in the micro-stratigraphic studies of samples taken from the painted walls of Oyola, an archaeological site situated in the northwest of Argentina, are presented. These samples have been analyzed by micro-Raman spectroscopy (mRS) and scanning electron microscopy with energy dispersive X-ray (SEM-EDS). The differences found by cross-section chemical studies could be explained as a consequence of two situations: 1- differences in the painting’s chemical components, either in the pigments involved or additives used; and, 2- differences in the physical properties of the mixtures such as stratum thickness and/or particle size. Also, in this article is explained each of the hypothesis, presenting the limits of these interpretations and pointing out future research challenges. As we discussed, it could be possible that the chemical and physical differences found between painting mixtures were the material expression of varied types of pictorial techniques.

Making visible the invisible. A microarchaeology approach and an Archaeology of Color perspective for rock art paintings from the southern cone of South America

“…They evaluate, for example, the consequences of the use of one technique over others and discussed the implication of the results obtained following the research questions raised. They also compared the advantages of elemental over crystallographic techniques, the use of scanning electron microscopy over other analytical techniques, the preparation of samples in resin for stratigraphic analysis, and its consequence for specific archaeological questions (Tomasini et al, 2012a andSepúlveda, 2009 andSepúlveda and Laval, 2010b;Sepúlveda and Wright, 2018;Gheco et al, 2017Gheco et al, , 2019Gheco et al, and 2020.…”

“…Despite these advances, very few studies have considered and reflected upon the nature and particularities of rock art paintings. Materially speaking, these paintings are a mixture of different components mixed and applied over a fragile rock surface and submitted to constant environmental agents (Boschin et al, 2011;Sepúlveda and Wright, 2018;Gheco et al, 2020). The human occupational history of the site contributes to forming complex microstratigraphies on rock art panels (Nazar et al, 2010;Tomasini et al, 2016;Gheco et al, 2017 and.…”

“…Some pigments could be heated to modify their properties (Pomiès et al, 1999;De La Fuente and Nazar 2016). The identification and characterization of the painting components can be obtained through elemental, molecular and crystallographic analysis, used single or combined according to the component to be analyzed and the research question (Chalmin et al, 2003;Vásquez et al 2008;Yacobaccio et al, 2008;Boschín et al, 2011;Huntley et al, 2011;Bonneau et al 2012;Chalmin and Huntley, 2017;Sepúlveda and Wright, 2018;Gheco et al, 2020). Then, before choosing a protocol for analysis it is inevitable to first understand the nature of the rock art paintings, i.e.…”

“…Once prepared according to the equipment's requirements, these samples can be analyzed through a combination of different techniques for the identification and characterization of their components, which have well-established and developed procedures in the study of rock art paintings abroad (Chalmin et al, 2003;Bonneau et al, 2012 and2016, for example). Surprisingly, in Argentina and Chile, very few studies have considered the microstratigraphic analysis of their samples to at least differentiate the composition of the rock surface, pigment layer(s) and superimposed patinas (Boschín et al, 2002(Boschín et al, y 2011Sepúlveda, 2009, Sepúlveda and Laval, 2010, Sepúlveda et al, 2012, 2013a, 2013b, Tomasini, 2012ay 2016Tascon et al, 2016;Gheco et al, 2017Gheco et al, , 2019Gheco et al, and 2020. On the contrary, many studies have used crushed samples for their analyses, so their results refer to the group of components present in all the sample's strata.…”

“…The limitation observed in most of the studies where stratigraphic analysis of samples has been considered is that in general, they have only regarded the observation of layers and their chemical composition. These studies omit in general the description and morphological characterization of the layer contents, as well as the quantification, measurement, and distribution of its components or grains present in each one (Marte et al 2011 and; to illustrate our purpose see Chalmin et al, 2003;Vignaud et al, 2006;Gheco et al 2020, as they describe precisely what we want to sustain here). As a consequence, chemical characterization of the different layers, the eventual quantification of their composition, and the mixtures identified are interpreted as the result of different mixtures, or different paint pots, in other words, the elemental and molecular differences correspond to different recipes (Chalmin et al, 2003;Vignaud et al, 2006;Bonneau et al, 2016).…”