Microbial activity and studies on excavated megalithic micaceous potsherds from Peninsular India

Abstract

The abundantly available mica flakes were added in raw materials to manufacture pottery in Central Peninsular India during the early Iron Age (700-300 BCE) for storage and glittering. The micaceous potsherds from the excavated megalithic site of Nagpur were studied for their composition, manufacturing techniques, microstructural features, microbial colonization, and estimation of firing temperature. The analytical techniques used were micro-XRF, FTIR, XRD, FEG-SEM, mercury porosimetry (MIP), and thermal analysis. The XRF and SEM-EDX data revealed that the potteries were coated with aqueous iron oxide on either surface for red hue and subsequently fired at an estimated temperature of 700-750 °C in a reducing atmosphere as determined by vibrational and mineralogical analysis. The X-ray microscopy and FEG-SEM images showed a grey color sandwich layer representing the original clay composition between iron oxide-coated red surface layers. MIP showed that the fine ware had a high porosity of 21-26% with a void ratio (e) of 0.28-0.36. The loosely adhered mica flakes influenced the strength and stability of the pottery. The 16S rRNA gene sequencing identified the presence of Bacillus velezensis within the round and elongated pits within the potsherds drawing nutrients from minerals.