Archaeologists have attempted the interpretation of rock art, but have often disregarded the technical aspects of paints. Analysing paint samples for preparaWon techniques and studying the various compounds used, allows us to determine the technology of prehistoric painters. These artists used mainly two colours: red (iron oxide: natural hemaWte or heated goethite) and black (charcoal or manganese oxides). These pigments could be prepared in different ways (grinding, mixing with extender and/or binder or by heaWng) in order to enhance the properties of the paints. Analyses attempt to determine the physicochemical nature of the matter and its preparation mode, and to get an idea of its geographic provenience.
New challenges
Field investigation is complemented by laboratory work involving X-ray diffraction, scanning electron microscopy, Raman spectroscopy analyses and other archaeometric techniques of pigment characterization. Reconstructions of the recipes, based on chemical analyses, are being undertaken at different research laboratories to evaluate the chemical-mineralogical composition of the original pigments and to understand better the means of application to the rock. Data from these field and laboratory studies help us better to understand the stresses affecting the rock art paintings and their causes.
Many spectroscopic techniques are nondestructive and micro-destructive in nature, which preserves the cultural heritage objects themselves. Following a discussion of terminology related to mobile instrumental methods, results of a literature survey on their applications for cultural heritage objects is presented. Sections devoted to specific techniques are then provided: Raman spectroscopy, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, laser-induced breakdown spectroscopy, and less frequently used techniques. The future of these archaeometric approach will be focus on the combination of different instrumental techniques.
The challenge now is to evaluate and use these data to undertake real surface conditions that affecting rock-art and, hence, suggest possible protective or remedial actions. Also, with the development of the archaeometric techniques and recognition of the organic components, could be possible to apply absolute dating methodologies.
Hugo Gomes