jueves, 16 de enero de 2014

The chemistry of rock-art (Castilla La Mancha, Spain)

A team of researchers from the Spanish National Research Council (CSIC) analysed two examples of rock-art from shelters in Albacete in Spain – one from the Palaeolithic (10,000 years ago) and one from the Neolithic (6,500 – 3,500 years ago) in order to better understand the chemical composition of the pigments.
Different styles
The samples analysed correspond to two rock shelters of completely different painting styles; one known as Levantine and found in Abrigo Grande de Minateda, and the other as Schematic, as present in Abrigo del Barranco de la Mortaja.
Since its discovery, Abrigo Grande de Minateda has been hailed as emblematic of the origin and evolution of rock art in the Mediterranean Basin of the Iberian Peninsula and is a UNESCO World Heritage Site.
The bovid which was sampled is depicted  in Abrigo Grande de Minateda and was created by hunters-gatherers who inhabited the Iberian Peninsula around 10,000 years ago. The other sample comes from the more abstract depiction of a quadruped painted on the wall of  Abrigo del Barranco de la Mortaja. This style was developed by the first farmers who lived in the area between 6,500 and 3,500 years ago.
Four techniques
The team used four complementary techniques to identify and characterise the physicochemical properties of the paint and of the surface –Microphotography, Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDX), Raman Spectroscopy and Gas Chromatography–Mass Spectroscopy (GC–MS).
They found that the artists in both caves used iron oxides and earth materials as pigments all of which are easily found in the environment of the shelters.
Alberto Jorge, CSIC researcher at the National Museum of Natural Sciences, states: “The compositions of the pigments used in both styles, separated by several millennium in time are identical, which means that the artists did not turn to intentioned recipes as was previously thought. The truth is that it is an abundant and good-quality pigmenting material that was easy to find nearby”.
New interpretations
Another more important conclusion of the work has implications for research methodology.
The presence of calcium oxalate proves that the paint merged with the outer layer of the cave wall over the centuries. Jorge explains: “This result would question the studies conducted so far, based on distinguishing three stratigraphic layers – surface, pigment and patina, as these are continuously merged and altered, which introduces a clear random factor in the dating”. Researchers have also detected the presence of certain fatty acids, which would suggest that when pigments were processed, applied or stored, they could have come into contact with animal skins (perhaps used for storage.)
CSIC researcher adds: “From now on, we need to be very cautious when we talk about rituals in the preparation of pigments, as these interpretations came up when substances such as calcium phosphates, explained previously as charred and crushed bones, were found in the pigments. These extrapolations are not correct since we have also found these same substances in the rocky substrate itself”.

Source: Past Horizons: http://www.pasthorizonspr.com/index.php/archives/01/2014/the-chemistry-of-rock-art

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