J. Chil. Chem. Soc., 60, Nº 1 (2015) 2822 IN SITU X-RAY FLUORESCENCE ANALYSIS OF ROCK ART PAINTINGS ALONG THE COAST AND VALLEYS OF THE ATACAMA DESERT, NORTHERN CHILE MARCELA SEPÚLVEDA a *, SEBASTIAN GUTIERREZ a , JOSÉ CARCAMO a , ADRIAN OYANEDER a , DANIELA VALENZUELA b , INDIRA MONTT c , AND CALOGERO M. SANTORO d,e a Laboratorio de Análisis e Investigaciones Arqueométricas, Departamento de Antropología, Universidad de Tarapacá, Camino Azapa Km 12, Arica, Chile. b Departamento de Antropología, Universidad Alberto Hurtado, Almirante Barroso 10, CP 6500620, Santiago, Chile. c Instituto de Investigaciones Arqueológicas y Museo, Universidad Católica del Norte, calle Gustavo Le Paige s/n, San Pedro de Atacama, Chile. d Instituto de Alta Investigación, Universidad de Tarapacá, Antofagasta 1520, Arica, Chile. e Centro de Investigaciones del Hombre en el Desierto (CIHDE), Av. General Velásquez 1775, Ediicio CIHDE, Arica, Chile. ABSTRACT Results of exploratory in situ analyses with a portable X-Ray Fluorescence (XRF) applied to six rock painting sites, located from Lluta to Camarones coastal valleys in the Atacama Desert, northern Chile, are presented. The results indicate the use of iron oxide as a main component in all paintings, alone or combined with aluminum silicate. Arsenic, a component highly present in water in the region, was also identiied, indicating the use of water as a possible binder or thinner. These output allow unraveling painting technology, a step forward to deine and understand the stylistic variability of rock art (engravings and paintings) in the context of the social changes and continuities of prehistoric communities. Additionally, it illustrates the effectiveness of portable XRF, a non-destructive analytical tool, applied for the irst time in the Atacama Desert. e-mail: msepulveda@uta.cl INTRODUCTION X-ray luorescence (XRF) is one of the most common techniques applied in conservation and archaeology 1-3 , specially in Europe and the United States, because of its ability to identify the presence of elements in major and minor amounts, and its non-destructive and non-invasive method of application. The improvement of portable equipment has contributed over the last 40 years to increasing its use, as, in many cases, it allows in situ analysis without sample extraction. This technique is also valued for its relatively low cost and short period of analysis 3 . The use of portable instruments, such as Raman and especially X-ray luorescence, has proven quite useful for the physical- chemical characterization of Paleolithic art and more recently for rock paintings by contributing to their preservation and preventing unnecessary sampling 4-11 . In contrast, until recently, most of the work undertaken in Chile to identify paint components has involved invasive and destructive laboratory sample analysis methods, by means of X-ray diffraction 12-14 or scanning electron microscope combined with energy dispersive X-ray spectroscopy 15-19 . Moreover, rock art paintings have been generally studied as images or iconographic representations, while the material aspects of these visual manifestations have been ignored because, among other issues, the lack of trained people in these methods and techniques, and the absence of specialized laboratories in Chile, of the kind where these samples were processed. Paintings are embedded in complex production processes, from obtaining raw materials up to applying them onto a wall, followed by its subsequent use, maintenance, recycling, discarding or abandonment 20-22 . The selection or use of speciic formulas in rock art painting can be as stylistic as the production of the images themselves. A igure is stylistic when it displays a selection of attributes of the real referent combined and arranged in a regular and speciic way 23 . The composition of the panels, the use of certain techniques, and the selection of certain platforms or spaces can also relect stylistic decisions. Thus, XRF analyses can help to ind out whether dissimilar painting components or combinations of elements were used in rock art styles. In future research, we aim to strengthen the relation between physic and chemical results and cultural changes in the prehistory of northern Chile. Along the coast and valleys of the Atacama Desert, in northern Chile, rock painting is a rare form of expression—only 8 sites have been identiied to date— which contrasts with the large number of engravings and geoglyphs recorded. These images were created during a wide temporal range, from the Formative period or “Andean Neolithic” time (ca. 2500 B.P) up to the beginning of the European colonial era (16th century) 24-25 . The deinition and understanding of the stylistic variability of rock art (engravings and paintings) in the context of the social changes and continuities in the study area has been recently addresed 26 . Thus the study of the composition of rock paintings is a different way to approach this thorny universal problem. Particularly, the stylistic and chronological framework for the Atacama Desert paintings continues to be uncertain, as most of the studies have concentrated on engravings and geoglyphs 24-26 . Besides, the motifs depicted in paintings are composed of geometric or indeterminate forms, making it dificult to compare them with iconography better chronologized, portrayed by means of other techniques and in different media (textiles, gourd pyro engraving, for example) 27 . This study demonstrates the advantages of XRF portable instruments in determining the elemental characterization of rock paintings in the Atacama Desert, without destructive sampling. Also we contribute to paintings preservation. MATERIAL AND METHODS Six sites were analyzed, which included from north to south and from the Paciic Ocean inland: La Capilla-1 situated south of the mouth of the Azapa Valley; Vitor-3a located at the mouth of the Chaca valley (known as Caleta de Vitor); Ofragía-1 and Cruz del Siglo-1 located in the middle reaches of the Codpa Valley; Camarones-19 at the mouth of the valley of Camarones and Huancarane-1 in the middle reaches of this valley (Figure 1). These sites are spread over three of the four main valleys that traverse the Atacama Desert merging into the Paciic shore 28 . All painting rock art are in color red. All igures analyzed are generally small (up to 20 cm). Only Huancarane and Ofragía 1 present two larger igures of ca. 50 cm. Figure 1. Map of rock art painting sites at northern Chile.