In-depth analyses of paleolithic pigments in cave climatic conditions

Abstract

Painted caves are a specific environment which preservation needs multidisciplinary studies carried out within the different actors. The actions set-up must follow national and European ethics and treaties and be as less invasive as possible to preserve the integrity of the site. Studying colorants in caves should meet these expectations and take into account on-field conditions: high humidity rate, reduced access to electricity, etc. Therefore, non-invasive analyses should be preferred. However, their limits restrict the field of application and sometimes sampling and laboratory analyses must be used to answer the problematic. It is especially true when the pigment is covered by calcite. For this purpose, the Laser-Induced Breakdown Spectroscopy (LIBS) has been assessed to identify the composition with stratigraphic analyses. This study carries out in-depth profile on laboratory samples in conditions close to the ones meet in caves. Samples were prepared on a calcareous substrate using three pigments: red ochre, manganese black and carbon black and two binding media: water and saliva. All samples have been covered by calcite. Four sets of measurements have then been done using the LIBS instrument. The in-depth profiles were obtained using the Standard Normal Variate (SNV) normalization. For all the samples, the pigment layer was identified in the second or third shot, the calcite layer being quite thin. However, the results remain promising with the carbon black pigment but not really conclusive, the carbon being generally quite difficult to quantify.