PHYSICOCHEMICAL CHARACTERIZATION OF ROCK ART PIGMENT FROM KARIM CAVE, SANGKULIRANG- MANGKALIHAT, EAST KALIMANTAN, INDONESIA

• Main Author: Mu`alliful Ilmi, Moh.
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/45572
• Institution: Institut Teknologi Bandung

Rock art are carvings or paintings made in the prehistoric era on the surface of a rock or wall using certain pigment colours. Rock art research in Indonesia still focuses on the archaeological and anthropological aspects of rock art. While research on the physicochemical properties of the pigments has not been done much. In this study physicochemical characteristics of pigments were analysed using various characterization methods. This research is important to be carried out to determine the composition, preparation techniques and the importance of rock art preservation. Characterizations of pigment samples were done by combining characterization using X-rays-based synchrotrons (XRD and XANES), microscopy (SEM and ?-XRF), and spectroscopy (FTIR). Rock art pigment were collected from the Karim Cave site, Sangkulirang-Mangkalihat, East Kalimantan. These pigments have purple, dark red, and red colours. Purple and red pigments were taken from beehives-like and tapir images in Panel 1 of the Karim Cave site, while red pigment was taken from the hand stencil image in Panel 4 of Karim Cave site. The results of the identification of phase components using SR-XRD (Synchrotron Radiation-X-ray Diffraction) showed that these pigments containing calcite minerals (CaCO3), gypsum (CaSO4.2H2O), whewellite (CaC2O4.H2O) and hematite (Fe2O3). Further analysis of hematite peaks in plane (104) showed that the purple sample has the smallest FWHM due to a larger crystallite size and higher crystallinity than other pigments. This differences in each of them where purple pigments are prepared with pre-treatment by heating at higher temperatures compared to other pigments. Chemical composition analysis using XRF, showed that purple pigment has a higher hematite content than other pigment. In addition, the XRF characterization result found the content of calcium and sulfur oxides which correlated with gypsum and calcite minerals, which are minerals forming substrate rock images. The high iron content in the purple sample was measured by the results of the mapping. Identification of functional groups using FTIR on each pigment material showed an absorption at the wavenumber of 475-447 cm-1 obtained from the vibrations of Fe3+-O bonds. The intensity of absorbance in the absorption band of Fe3+-O bond in the purple sample was higher than other samples which indicated the higher content hematite as found in XRF method. Furthermore, the analysis of chemical species of the pigment material were carried out using Fe K-edge XANES, where the Fe K-edge XANES spectra showed the edge energy (E0) of each pigment sample located at 7126.6 eV which showed the character of Fe3+ species of iron. The pre-edge spectra deconvolution results show that the absorption ratio of t2g/eg in purple samples is lower compared to other pigments. The increase of eg peak intensity was probably due to the distortion of octahedral Fe coordination in hematite crystals which results in changes in electronic structure. These changes presumably affected by heating treatment of the pigmen materials. The alteration of the hematite structure from the octahedral to tetrahedral was also supported by the analysis of the location of the centroid peak in the pre-edge Fe K-edge XANES spectra, where the integration value of the pigment absorption sample will be used to determine the symmetry of the coordination of iron atom inside the hematite structure. The result showed that the iron atom was five-coordinated with C4v symmetry. While the dark red and red samples lie in the octahedral centroid position (Oh). The results of this study indicate the fact that pigments are derived from hematite minerals with different physicochemical properties. This difference is due to differences in pigment pre- preparation as the heating technique.