Iron Age beta (23% tin) bronze: Peninsular Indian bowls of Adichanallur,Nilgiris, and Boregaon

ABSTRACT

As-cast binary copper–tin alloys with over 15% were generally not much in use in antiquity as they get embrittled at higher tin contents due to the increasing presence of the intermetallic delta phase compound. Even so, the unusual and skilled use of a higher tin binary bronze alloy, known as wrought and quenched high-tin beta bronze, is found, especially from some Iron Age or megalithic sites in southern and peninsular India, around the early first millennium BCE. They are closely approximating to the composition of the pure beta phase of 22.9% tin, which is an intermetallic compound. This article presents some of the micro-structural evidence of heavily hot-forged, carinated, and perforated bowls from the site of Adichanallur, Tamil Nadu. They rank amongst the most finely wrought examples of beta bronze known in the world, with continuing traditions into the medieval Chola Tamil region and contemporary period. A process of experimentation with thermomechanical processes in the Peninsular Indian Iron Age is also suggested, since it slightly differed from an example of a vessel with 21% tin that was only cast and quenched, found in Boregaon from the Vidarbha megaliths of Maharashtra in the Central Deccan.