Scientific insights in the preparation and characterisation of a lead-based naga bhasma

Naga bhasma is one of the herbo-metallic preparations used in Ayurveda, a traditional Indian System of Medicine. The preparation of Naga bhasma involves thermal treatment of ′Naga′ (metallic lead) in a series of quenching liquids, followed by reaction with realgar and herbal constituents, before calcination to prepare a fine product. We have analysed the intermediates obtained during different stages of preparation to understand the relevance and importance of different steps involved in the preparation. Our results show that ′Sodhana′ (purification process) removes heavy metals other than lead, apart from making it soft and amenable for trituration. The use of powders of tamarind bark and peepal bark maintains the oxidation state of lead in Jarita Naga (lead oxide) as Pb 2+ . The repeated calcination steps result in the formation of nano-crystalline lead sulphide, the main chemical species present in Naga bhasma.