Determining the origins of particulates on Arkaroo Rock art

Arkaroo Rock, an important Aboriginal art site located in the Flinders Ranges National Park, South Australia, features a range of artworks created using red and yellow ochre along with white minerals (such as kaolinite, and gypsum) and charcoal. The site is widely promoted to tourists and, during peak season, attracts more than fifty visitors each day. In mid 2007, the local indigenous community noted that the art was covered with a dust-like substance, the nature of which was unknown. It was hypothesised that the substance was the result of local soil adhering to the surface of the artwork with the morning dew. In order to preserve the site, cleaning and conservation work began in early 2008. This study presents an investigation into the source of the particulate matter covering the artworks. Prior to the conservation work commencing, samples were collected from various locations on the rock, within the protective fence surrounding the artwork, and the surrounding soil. Plant samples were also collected proximal to the artwork. A number of techniques were used to characterise and identify the origin of the particulate material from the rock surface. These techniques included optical microscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), colour analysis based on the ES-1000 EFI spectrophotometer (UV-Vis), and subsequent multivariate statistical analysis. Results of this study are presented here, including detailed results obtained from an emerging colour-based ES-1000 EFI spectrophotometer method along with TGA, optical microscopy and XRD. Results confirm the presence of morning dew in surface samples, and eliminate local sources as the origin of the particulate matter.