Surface preparation and the effects on rock art deterioration

The Drakensberg is the highest part of a 1000-km long escarpment that also forms a natural border between South Africa and eastern Lesotho. The uKhahlamba-Drakensberg Park was declared a World Heritage site in 2000 and is globally significant, in particular due to the rock art painted by San hunter-gatherers who inhabited the area from about 8 000 years ago until the late 19 Century. Approximately 30 000 painted images can be found in nearly 600 rock shelters in the area. Rock art heritage in the Drakensberg is unfortunately being lost through a variety of processes, some natural and others resulting from human impacts. Previous research on the weathering of San paintings has focused largely on either monitoring processes causing weathering in rock shelters or investigating rock surfaces that are adjacent to the rock paintings. Recent findings indicate that some of the San art has been painted onto surfaces that were prepared by smoothing the rock surface with a “grinding stone” and coated with a clay (“ground”) layer prior to the application of pigments. This new information may have important implications for rock art conservation as smoothing of a rock surface could significantly modify the physical and chemical characteristics of the surface, thereby influencing the deterioration of the art. In this study two classification systems are developed from data collected in four rock shelters situated in the Park. The first, a Type of Surface Classification System, is developed for the purpose of identifying different types of rock surfaces within rock shelters. The second, a State of Deterioration Classification System, is developed with the purpose of establishing, through visual inspection, how deteriorated the rock art on different types of rock surfaces is. Linkages between the type of surface and the state of deterioration are also explored. Findings show that it is not only possible to determine which surface type a painting has been painted on, but that different rock surface types can deteriorate through different weathering mechanisms and to a iv different degree. One type of rock surface, acknowledged but not yet recorded, was found amongst the rock art paintings selected for the purpose of this study. More importantly, the alteration of rock surfaces through human action in the past is found to cause rock surfaces to deteriorate either at an accelerated or a retarded rate as opposed to rock paintings that were made on surfaces that have only been altered by natural weathering mechanisms. For example, if a rock surface has only been smoothed with a grinding stone, results show that weathering mechanisms did not deteriorate the surface as quickly as in the case where a clay ground layer has been applied to the rock surface. Different types of rock surfaces deteriorating through different weathering mechanisms (as a result of surface preparation) might have significant implications in terms of rock art conservation as the strategies implemented to conserve rock art should be adapted to consider surface type. In terms of rock art studies aiming to conserve this precious heritage, the two classification systems presented could, therefore, be useful non-destructive tools in assessing rock art deterioration.