The first <i>in situ</i> Raman spectroscopic study of San rock art in South Africa: procedures and preliminary results

TLDR

Southern Africa’s rock art, created by hunter‑gatherers, herders, and farmers, has a rich heritage but has been rarely chemically analyzed because previous methods required destructive sampling. This article reports the first worldwide in‑situ Raman spectroscopic study of South African rock art, aiming to test a portable instrument’s performance, analyze paint technology, and evaluate its conservation value. Researchers used a portable Raman spectrometer on paintings from two distinct sites, carefully controlling laser power to identify pigment layers and alteration products in situ. The instrument proved highly suitable for challenging field conditions, successfully identifying known pigments and alteration products and revealing a layered pigment–alteration structure for the first time in situ. © 2010 John Wiley & Sons, Ltd.

Abstract

Abstract 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. Copyright © 2010 John Wiley &amp; Sons, Ltd.