Rock, pigments, and weathering. A preliminary assessment of the challenges and potential of physical and biochemical studies on rock art from southern Ethiopia

Over the past decade, physical and chemical analyses have been widely applied to the study of rock art contexts, particularly to examine the composition of rock art paintings and for direct radiometric dating. Different sampling and analytical methods have been applied to rock art from different parts of the world. However, in Africa these analyses are still at an embryonic stage. The results are often problematic in terms of reliability, mainly as concerns the chronology. This is due to a wide range of fossil and active biodegradation processes affecting rock surfaces and pigments; such processes are still widely underestimated. This paper aims to discuss the state of the art of the physical and chemical analyses undertaken on African rock art contexts, and the urgent need to establish protocols and best practices for sampling and analysis. The preliminary results of a new project in southern Ethiopia are presented here as an example of an integrated study of a rock art context, combining Archaeology and Earth Sciences. Preliminary field observations and SEM-EDS analyses, run on samples from two rock shelters in the Borana area, reveal the presence of a complex set of physical, chemical, and biological weathering processes with manifold effects on the rock art evidence.