Deterioration of San Rock Art: New Findings, New Challenges
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Research in Action South African Journal of Science 103, September/October 2007 361 ground—see below) and thus may work Deterioration of San rock art: synergistically with the thermal stresses. A further new observation,7 applicable New findings, new challenges to some paintings (but not all) found in the Drakensberg area, is that the surface on which a painting (or paintings) was a,b* b c Kevin Hall , Ian Meiklejohn , Joselito Arocena , created had been both smoothed, probably Linda Prinslood, Paul Sumnerb and Lyndl Halle with a water-polished stone (such stones were observed on the floor at all the sites investigated), and covered with a (white) he heritage of San rock art in southern whewellite, quartz and alumino-silicate clay-based ground (Fig. 1). Application of Africa is globally acknowledged, and minerals, with haematite providing red a mineral-based ground (huntite) for Twas one of the primary reasons for the colouration in the ochre pigment and paintings has also been reported from successful nomination of the uKhahlamba/ gypsum (and perhaps gum from aloes3,7) Australia, where such ground was found Drakensberg Park in South Africa as a World Heritage Site.1 Deterioration of rock paintings the source of the white attribute of the to be predisposed to advanced deteriora- in the reserve could adversely affect the inter- white pigment. Both pigments may have tion, especially under damp or humid national status of the region, particularly as plant sap as the origin of the whewellite, conditions.11 Both the smoothing and the little has been achieved with regard to pre- where that has been used as a binder clay-based ground significantly modify serving the art for future generations. A study and/or whitener.3,7 These findings appear the physical and chemical characteristics is currently under way in the Injisuthi and to be consistent with those for other rock of the surface. Smoothing of the rock Giant’s Castle areas of the park, to investigate art sites in the world10–12 and with previous changes surface porosity and increases the deterioration of San art; this article serves studies from southern Africa.17–20 Pigment strength,8 and also serves to remove any to introduce the project and to highlight some initial findings. Previous research on the mineralogy not only affects chemical weakened, weathered surface that would 9 weathering of San paintings has focused responses but also has a significant influ- otherwise be beneath the painting. It is largely on either monitoring rock shelters2 or ence on thermal properties,3 which can the application of a clay-based ground, investigating rock surfaces that are adjacent lead to pigment-to-pigment as well as however, that is perhaps more significant to the paintings. None of the methods applied pigment-to-rock stresses. Thermal infra- to longevity of the paintings. The clay- in earlier investigations has considered the red data have shown that the rock and based ground acts as an impermeable interface between rock and pigments, mainly both the white and ochre pigments have barrier for moisture flow, both into the because of the potential damage that may result quite different responses to solar heating, rock and from the rock to the air; it also from the use of tactile monitoring equipment. 3 Recent advances in weathering research, using which can be explained by the differ- greatly changes thermal properties. 3 improved techniques to measure conditions ent thermal properties of the materials. Furthermore, observations suggest that at the rock surface where the San art is painted,3 Where exposed to solar radiation, there- in many instances what was interpreted provide new insights into surficial processes fore, the materials comprising the paint- as weathering of rock is, in fact, loss of the and suggest new lines of investigation. ings and painting–rock associations may clay attachment to the rock (Fig. 1), and well experience shearing forces that cause this has ramifications for remediation or New findings cracking10 and, ultimately, failure. Changes preservation. New data, primarily from the Main in humidity can produce the same physi- The pigments, at least where there is a Caves at Giant’s Castle and at Battle Cave cal outcome (cracking of the clay-based clay base, do not penetrate the rock, but at Injisuthi, in the uKhahlamba/Drakens- berg Park, South Africa, show that the rock surface onto which San art is painted, the preparation of this surface, and the nature of the paints themselves influence pigment response to the ambient environ- ment. A key attribute of the application of pigments to rock, or indeed to any surface, is that they comprise a surface modifier.3,4 The pigments alter the surface’s albedo, porosity, chemistry, and thermal proper- ties, and this becomes even more complex5 if there are multi-layer paintings (such as those at Tandjesberg6 in the Free State). Recent studies,3 as with some earlier in- vestigations,20 have shown that both white and ochre pigments contain aGeography Programme, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada, V2N 4Z9. bDepartment of Geography, Geoinformatics and Meteo- rology,University of Pretoria, Pretoria 0002, South Africa. cSoil and Environmental Science, University of Northern British Columbia. dDepartment of Physics, University of Pretoria. Fig. 1. A typical example, from the Giant’s Castle area, of an ochre painting on a clay-based ground that exhibits eHexagram/XS Labs, University of Concordia, Montreal, disassociation of the ground from the underlying rock as a result of weathering. Also illustrated are examples QB, Canada, H3G 1MB. of striae (scratches) associated with the surface cleaning and preparation of the painting surface prior to *Author for correspondence. E-mail: [email protected] application of the thin ground layer. 362 South African Journal of Science 103, September/October 2007 Research in Action occur as discrete layers on the rock (see This can lead to shearing forces that may Ancillary studies, notably analyses of the Fig. 4 of Hall et al.3). In terms of weathering induce cracking13 and deterioration at the pigment composition, field-based Raman and conservation, therefore, consideration painting–rock interface, and also facilitate spectroscopic analyses of paintings, and must be given to maintaining the clay– the admission of endolithic organisms,15 the application of a new approach for rock bond or, otherwise as in Fig. 1, the leading to further deterioration. classifying painting panels in terms of painting deteriorates; not through weath- weathering attributes, are also being ering of the rock but as a result of separa- New challenges undertaken at other sites within the tion of the clay from the rock. Changes in On the basis of the above observations uKhahlamba/Drakensberg area. environmental conditions, notably of and findings,4,8,10,16 researchers at the uni- moisture and temperature, are suggested 1. UNESCO (2000). Report of the 24th session of the versities of Pretoria, South Africa, and of World Heritage Committee, 27 November 2000 – to affect the stability of the pigment– Northern British Columbia in Canada are 2 December 2000, Cairns, Australia. 3,13 3,7,15 clay–rock bonds. It is argued that undertaking a detailed in situ study of the 2. Hoerlé S. and Salmon A. (2004). Microclimatic both climatic change and local, human- key parameters associated with the data and rock art conservation at Game Pass Shel- ter in the Kamberg Nature Reserve, KwaZulu- induced environmental changes may weathering of San rock art exposed, at Natal. S. Afr. J. Sci. 100, 340–341. cause loss of stability of the rock–clay least in part, to solar radiation (at Giant’s 3. Hall K., Meiklejohn I. and Arocena J. (2007). The and clay–pigment bonds and, through Castle Main Caves). Field investigation is thermal responses of rock art pigments: Implica- other mechanisms,14 also affect San paint- tions for rock art weathering in southern Africa. complemented by laboratory work in- Geomorphology 91, 132–145. ings that are not on a clay base. It is also volving X-ray diffraction, scanning elec- 4. Bullet T.R. and Prosser J.L. (1983). Paint: A surface suggested, in respect of human-induced tron microscopy and Raman spectroscopy modifier. Phys. Technol. 14, 491–500. changes,3 that the removal (or loss) of analyses of pigments and pigment–rock 5. Mecklenburg M.F.,McCormick-Goodhart M. and Tumosa C. (1994). Investigations into deteriora- trees, largely for visitor purposes, at sites associations. Reconstructions of the pig- tion of paintings and photographs using comput- such as Giant’s Castle Main Caves, has ments, based on chemical analyses, are erized modeling of stress development. J. Am. influenced ambient thermal and humidity being undertaken at a fine arts research Inst. Cons. 3, 153–170. conditions, thereby affecting the paint- 6. Loubser J.H.N. (1993). A guide to the rock paint- laboratory at the University of Concordia ings of Tandjesberg. Nav. Nas. Mus. (Bloem- ings and possibly resulting in accelerated (Montreal, Canada) to evaluate the hues fontein) 9, 345–384. deterioration. Global climatic changes, and tones of the original pigments and to 7. Arocena J.M., Hall K. and Meiklejohn I. (in press). particularly those leading to increased understand better the means of applica- Minerals in pigments and their relevance to the origin and implications to conservation of San precipitation and humidity, would serve tion to the rock—the outcomes of this rock art (South Africa). Geoarchaeology. to exacerbate the situation. investigation will be used in laboratory 8. Katz O., Reches Z. and Roegiers J.C. (2000). Evalu- In instances where the paints cover the simulations (see below). At the field site, ation of mechanical properties using a Schmidt 37 clay ground (as observed in Fig.