TRANSFORMATION OF HEMATITE STRUCTURES AND COLORS: REVEAL PIGMENT PREPARATION TECHNIQUE OF PREHISTORIC ROCK ART IN INDONESIA

• Main Author: Nurdini, Nadya
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/72962
• Institution: Institut Teknologi Bandung

Prehistoric rock arts are a form of artwork made on rock surfaces and contain information about past life, including prehistoric human daily life, rituals/beliefs, inter-epoch communication, and social status in a community. Currently, the oldest rock art in the world is found in Leang Bulu Sipong, South Sulawesi, with an estimated age of 43,900. This finding encourages multidiscipline studies, especially regarding Indonesian rock arts. Several researchers have conducted multi-analysis studies of rock art to obtain archaeological information on pigment sources, composition, and preparation processes before being applied as rock art pigments. Hematite is a natural pigment used at almost all rock art sites worldwide. Hematite pigments, composed of iron(III) oxide compounds, have the characteristics of soft, reddish rock and high weather resistance. Apart from red, hematite is a purple pigment in various rock art sites. Previous studies have exhibited that the purple pigment is formed due to thermal treatment in the form of combustion. The treatment can affect the hematite's structure, morphology, and composition, causing a color transformation of the hematite. In this study, an analysis was carried out to analyze the effect of combustion temperature (between 600 ? - 1,100 ?) on the color change of hematite to obtain a detailed understanding of the process of transforming the color and structure of red hematite into purple and determine the dominant factors affecting the color change of hematite. So, the results of this study can see the trend (tendency) of color changes that occur in hematite due to combustion treatment at certain temperatures. Based on the observations, the synthesized hematite shows a color discrepancy from red to black- purple when calcinated at 1.100 ?. The particle size is increased and then forms a hexagonal shape characteristic of hematite. In addition, the crystal size and the crystallinity of the synthesized hematite also increased inlined with calcination temperature. Meanwhile, the ratio of the peak intensity of t2g/eg orbitals in the samples decreased and showed distorted octahedral symmetry distortion was intensified, resulting in a wavelength shift of light that was absorbed by hematite followed by hematite with darker (purplish) color. In excavated hematite obtained from Jarie Cave, Maros, South Sulawesi, the calcination temperature up to 1.100 ? does not produce a purplish color due to the presence of other minerals such as quartz and alumina (from clay). Thus, the presence of other minerals can affect the thermal transformation in hematite, especially if the composition of other minerals is sufficiently massive. Moreover, the analysis of color shift carried out using the CIE L*ab color space between the two types of hematite shows the same shift direction, from the red-yellow color to the blue-green color space. The same result of color shift from both hematites indicates that high temperatures thermal treatment can transform the color of natural hematite to a darker hue (purplish material) when the hematite has high purity. Based on the analysis of both types of hematite samples, it can be concluded that heating is one of the factors that cause changes in the crystal properties, morphology, and particle size of hematite, which then causes changes in the color of hematite to purplish. An understanding of the influence of these factors on hematite color transformation is expected to provide comprehensive information so that it can be concluded that the preparation technique occurs when the pigments are used as a medium for depicting prehistoric rock arts.