Rock Art Painting Taphonomy: the Role of Environmental and Technological Factors

Abstract

This work aims discussing the contribution of environmental and technological factors in rock art painting preservation, based on a 3-year experimental program and two archaeological cases from Patagonia (South America). Concerning technological factors, microscopic information of experimental and archaeological contexts indicate that fine-grained pigments have a better preservation potential than coarse-grained ones, likely related to the high binder adsorption capacity of silty and clay size particles, resulting in a strong pigment agglutination and substrate adherence. Mechanical entrapment/translocation of such small particles into the substrate further contributes to preservation. The experiment also evidences that blood-bearing paints present preservation advantages over fat/water-based ones, probably due to clotting and drying processes which agglutinate pigments and seal rock voids, avoiding binder migration. In contrast, experimental gypsum- and, to a lesser extent, charcoal-based paints show a rapid and significant deterioration, particularly in the temperate and humid context. The low archaeological expectancy derived from these results is supported by the scarce and/or ambiguous regional representation of these black pigments in ancient Patagonian paintings. Among natural factors, water-related processes (i.e., rainfall, snow, freezing and water infiltration) play a decisive role in the physicochemical paint degradation, also favoring bioactivity. Raman spectroscopy of neoformed white crystals in experimental paints may evidence, in a short term, a first stage of the profuse biomineralizations archaeologically observed, associated with lichens, fungus, and endolithic organisms. Finally, sheep rubbing and wind abrasion are proposed as the main agents affecting vertical frequencies and integrity of archaeological motifs at the cave and open-air contexts, respectively, whereas differences related to cardinal insolation likely impact in frequencies, motif color and weathering stages at the open-air site too.