The first in situ Raman spectroscopic study of San rock art in South Africa: procedures and preliminary results
Southern Africa has a rich heritage of hunter-gatherer, herder and farmer rock art traditions made by using both painted and engraved techniques. Until now, there have been only a handful of studies on the chemical analysis of the paint, as all previous types of analysis required the removal of pigment samples from the sites a practice which has been avoided. Raman spectroscopy is an ideal techniques to analyse the paint non-destructively and also offers the possibility of in situ work with portable instruments. This article describes the procedures and reports the preliminary results of the first in situ Raman spectroscopic study of rock art in South Africa (also a first worldwide), where we, first, evaluate the capability of a Raman portable instrument in very difficult conditions, second, analyse the paints in order to contribute to a better knowledge of the technology used and, third, evaluate the possible contribution of in situ analyses in conservation studies. The paintings from two different rock art sites were studied. The instrument proved to be highly suitable for in situ analyses in physically very challenging conditions. Most of the pigments and alteration products previously detected under laboratory conditions were identified, thereby giving information on both the pigments and conservation state of the paintings. A layered structure of alteration products and pigment was identified in situ for the first time by controlling the laser power, thereby obtaining the same results as in mapping experiments of cross sections of paint.