Multi-analytical characterizations of prehistoric rock art pigments from Karim Cave, Sangkulirang-Mangkalihat site, East Kalimantan, Indonesia

This study introduced various characterization methods to determine the physicochemical properties of rock art pigments. The pigments were obtained from the Karim Cave, East Kalimantan. The pigments have purple, dark red, and red colors. The results of the characterization by using SR-XRD (Synchrotron Radiation-X-ray Diffraction) show that these pigments have the main content of calcite (CaCO3), gypsum (CaSO4.2H(2)O), whewellite (CaC2O4.H2O) and hematite (Fe2O3). Chemical analysis by using XRF showed that purple pigment has a higher hematite content than other pigments. The identification of functional groups by using FTIR on each pigment sample showed an absorption at the wavenumber of 475-447 cm(-1) originating from the vibrations of the Fe3+-O bond. Furthermore, the electronic transition properties of the pigment material analyzed using Fe K-edge XANES show that the edge energy (E-0) of each pigment sample is located at 7126.6 eV which indicates the Fe3+ iron species. The results of the deconvolution of pre-edge spectra show that the absorption ratio of t(2g)/ e(g) in purple sample is lower compared to other pigments. The difference was caused by the distortion of octahedral coordination in hematite crystals that results in electronic structure changes. The distortion was also confirmed in the analysis of the centroid peak in the pre-edge spectra, where the integration value of the absorption intensity of the purple pigment sample was higher, compared to other samples. The results of this study indicate that the three pigments are derived from hematite minerals with different physicochemical properties.