Archaeometric Study of Pigment Materials on Megalithic Rock Art in Stone Chambers of the Pasemah Plateau, South Sumatra, Indonesia

Moh Mualliful Ilmi1*, Rr Triwurjani2, S. E. Prasetyo1, E. Maryanti3, N. Nurdini4, R. Y. Bahtiar1, and E. Chalmin5

The Pasemah Plateau in South Sumatra is a major Indonesian megalithic landscape, notable for its polychromatic rock art painted on slabstone surfaces within stone chambers. These rock art panels depict anthropomorphic and zoomorphic figures, plant motifs, ceremonial objects, and geometric patterns. The Pasemah tradition is thought to relate to the broader Dong Son cultural sphere, supported by Dong Son-style drum iconography in sculptures and rock art. This study investigates the physicochemical characteristics of Pasemah megalithic rock art pigments through stereo microscopy, Micro-XRF, SEM-EDS, Raman spectroscopy, and synchrotron HR-XRPD. Microscopy reveals variably thick pigment layers applied on weathered tuffaceous volcanic slabstone. Micro-XRF shows Fe-rich compositions in red and yellow pigments and Al-Si dominated composition in white and black pigments, suggesting clay-rich matrices and possibly related to the substrate influence. SEM-EDS corroborates these results by demonstrating Fe-rich clay matrices with diverse morphologies and ubiquitous small fine-grained iron oxides. Raman spectroscopy then confirms the result of former characterizations with hematite, goethite, sanidine (K,AlSi3O8), and charcoal as main component of red, yellow, white, and black pigments, respectively. HR-XRPD refines the results with information regarding mineral assemblages consistent with volcanic tuff substrates and clay-rich pigment matrices, including plagioclase, feldspar, pyroxene, and silica polymorphs. The diverse physicochemical properties of the pigments highlight the uniqueness of Pasemah megalithic rock art. This study significantly contributed for understanding the properties of pigment materials of megalithic rock art depicted on the volcanic tuffaceous slab stone context.