Non-Destructive Portable Analytical Techniques for Carbon In Situ Screening Before Sampling for Dating Prehistoric Rock Paintings

Abstract

Direct dating of prehistoric paintings is playing a major role in Paleolithic art studies. Very few figures can be directly dated since the necessary condition is that they contain organic carbon-based material. Thus, it is very important to check the presence of organic carbon-based material in situ before sampling in order to protect the visual integrity of the paintings or drawings. We have tested and compared 3 different portable analytical systems that can be used in cave environments for detecting carbon in prehistoric paintings: (1) a very compact X-ray fluorescence (XRF) system in Villars Cave (Dordogne, France); (2) a portable micro-Raman spectrometer in Rouffignac Cave (Dordogne, France); and (3) an infrared reflectography camera in both caves. These techniques have been chosen for their non-destructiveness: no sample has to be taken from the rock surface and no contact is made between the probes and the paintings or drawings. The analyses have shown that all the animal figures have been drawn with manganese oxides and cannot be directly dated by radiocarbon. However, carbon has been detected in several spots such as black dots and lines and torch marks. 14C results were obtained from 5 torch marks selected in Villars Cave, with ages between 17.1–18.0 ka cal BP. Three methods were used to identify carbon in black pigments or to confirm the presence of torch marks by carbon detection. Thanks to these new analytical developments, it will be now possible to select more accurately the samples to be taken for 14C dating prehistoric paintings and drawings.