On-field Raman spectroscopy of Patagonian prehistoric rock art: Pigments, alteration products and substrata

Abstract

An extensive in situ Raman spectroscopic campaign was performed on archaeological sites in three different provinces in Patagonia, Argentina (Neuquén, Río Negro and Chubut). 16 open air shelters located in different environments (forests, ecotones, steppes) were investigated and interpreted in terms of pigments used and the identification of substrata. Special attention was given to the alteration products and accretions that were found on the rock art paintings of the shelters and on the surface of the rock walls, as they can affect and damage this magnificent works of art. Haematite (α-Fe 2 O 3) was the main chromophore that was found on the red paintings of the most of the shelters studied. The green earth glauconite, was identified only in one case, by using a red (785 nm) and a green laser (532 nm). Other minerals and silicates were found on the couloured areas but also on the rock support. Calcite (CaCO 3) and gypsum (CaSO 4 •2H 2 O) crystallization was identified on the paintings, crusts and rock surfaces, in combination or alone, and are associated with weathering. In some cases the shelters were so severely degraded that no Raman signal of pigments and/or other components could be retrieved. Calcium oxalates were also detected in several figures and motifs in different shelters.

A Raman micro-spectroscopy study of 77,000 to 71,000 year old ochre processing tools from Sibudu, KwaZulu-Natal, South Africa

“…Anatase and quartz frequently merge with other compounds on Raman spectra acquired on rocks, as was also, for example, the case in the study of rock art from Patagonia [47] as well as for the previous studies of Sibudu tools [14,23]. Anatase and quartz are also regularly found in sediments and they derive from rock decomposition [14,23,[48][49][50].…”

“…The band around 660 cm −1 is often attributed to magnetite (Fe 3 O 4 ) in the literature [33,55], or even to the presence of kaolinite [56], but it is clearly present on the xx polarisation configuration performed on a single haematite crystal at low laser power [57] and is then part of the haematite spectrum. This band is also considered dependent on the degree of crystallinity [47].…”

Raman spectroscopy in experimental rock art: Improving the study of ancient paintings

“…The manufacture of paintings used here is exhaustively described in Ozán et al (in prep) and follows archeological and ethnographical data from Patagonia, southern South America, which is located between latitude 38° and 55°S. [ 18,24,26,35–47 ] Therefore, all raw materials used in mixtures were collected in this region, where red (i.e., hematite, maghemite, goethite, jarosite, and magnetite), white (i.e., illite, gypsum, kaolinite, feldspar, and calcite), and black (i.e., Mn‐oxides and charcoal) colors in rock art are ubiquitous (Table 1) [ 18,20,24,42,43,45–56 ] . On the other hand, the presence of fat as binder is well‐documented by ethnographic evidence, though it was only registered in two archeological contexts.…”

Arqueología y Biogeografía humana en el lago Nahuel Huapi: evaluando el rol del ambiente boscoso-lacustre norpatagónico y su vinculación con la estepa

“…Estas diferencias en cuanto a las técnicas y paletas de colores utilizadas brindan información relevante, ya que, si bien es posible que su producción estuvo fuertemente condicionada tanto por el tipo de materias primas disponibles para la selección de los soportes y la elaboración de los pigmentos, como del conocimiento para su acceso y aprovechamiento, es factible pensar que la elección del color posiblemente estuvo mediada por aspectos sociales y/o culturales. No obstante, es necesario mencionar que en el caso del ecotono y la estepa es posible encontrar diferentes minerales cromóforos para realizar una variedad significativa de colores (Rousaki et al, 2018, Vázquez et al, 2010. Esto último, no se ha comprobado para la zona del Nahuel Huapi, ya que lo que más abunda son los óxidos de hierro (de color rojo) principalmente bajo la forma de hematita que se encuentran en los aleros y/o abrigos rocosos .…”