Mud Plaster Wall Paintings of Bhaja Caves: Composition and Performance Characteristics

The historic mud plaster of Bhaja caves dated back to 1 st century BC to 3 rd century AD were investigated for their mineralogical, micro -structural and chemical characterisation. The analytical studies were performed using petrological microscope, thin section analysis, XRF, Laser particle size analyser, FTIR, XRD and scanning electron microscope. The traditional mud plaster is applied in two layers and thickness of inner layer depends on the topography of the basaltic stone surfaces. From the analytical examinations, it appears that in high rain fed regions of India's Western Deccan, fine clayey soil (clay>65%, sand 20-28% and silt 7-15%) has been sourced for the preparation of earliest mud plaster of Bhaja caves and its properties modified by deliberate mixing of slaked lime, sand and proteinaceous adhesive to enhance cementing properties. SEM photomicrographs reveal presence of elongated kaolinitic 'verm' and inter wired filamentous clay ribbons of illite-sepiolite in the plaster. The shrinkage property of the plaster has also been modified by addition of rice husk as vegetal additives. The present study favours methodological approach for preparing compatible mud plaster needed for the restoration of Bhaja caves.