The first in situ micro-Raman spectroscopic study of prehistoric drawings found in the cave of Rouffignac-Saint-Cernin (Dordogne, France) was carried out. Rouffignac cave art, assigned to the upper Magdalenian Paleolithic period (13500-12000 BP), is constituted of more than 250 drawings and engraving including 158 mammoths. There are about a hundred drawings, all made of black pigments. Until now, destructive chemical analyses performed on one sample, as well as recent micro X-ray fluorescence (m-XRF) in situ analyses have shown that the drawings contain manganese oxides. Because no carbon has yet been found, no direct dating of the drawings could be performed. This new study of the Rouffignac cave using non-destructive in situ micro-analyses aims at confirming or not the absence of carbon-based drawings and at understanding the apparent homogeneity of the parietal representations by the identification of the crystalline phases constituting the black pigments. The adaptability of portable equipment as well as the feasibility of in situ micro-Raman analyses in a cave environment was tested. The results obtained are compared with in situ XRF, and X-ray diffraction microanalysis is performed at the same time in the cave. We demonstrate that a portable Raman instrument is very useful to analyze non-destructively drawings in the following difficult conditions: high humidity, various wall geometries, and small amounts of material studied. These results show that the black manganese oxides romanechite and pyrolusite were used as pigments by prehistorical artists. Carbon and carotenoids have been found locally. Differences between the various figures are highlighted and hypotheses about the drawings production are proposed.
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.
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