A multianalytical investigation of the physicochemical properties of white rock art pigments at the Nali and Tene Koro sites, Lembata, East Nusa Tenggara, Indonesia

Abstract

Nali and Tene Koro are Austronesian rock art sites located in Lembata, East Nusa Tenggara, Indonesia. At both sites, rock art images are painted on the surfaces of outcrop boulders. The rock art depicted at the Nali site is characterized by an anthropomorphic grayish-white image, while rock art at the Tene Koro site depicts a white boat equipped with an up-raked stern, a single mast, and a steering paddle. Since it was reported in 2018, information regarding the physicochemical properties of white pigments used at both sites remains unknown. Herein, a combined analytical strategy was employed to understand the physicochemical properties of the pigment used at the Nali and Tene Koro sites. Several characterization methods, including X-ray fluorescence (XRF), optical microscopy, secondary electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), vibrational spectroscopy (Raman and FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric-differential thermal analysis (TG-DTA), were applied. The results demonstrated that the white pigment at the Nali site consists of gypsum as a major component and other clay minerals incorporated as minor phases as part of the geological formation of gypsum. On the other hand, the white pigment from the Tene Koro site comprises calcite as the main constituent and minor amounts of sulfur-bearing minerals (gypsum) as calcite weathering products. To the best of our knowledge, this is the first report of a physicochemical study of white pigments used in rock art in Indonesia.