What is "rasayana"

Rasāyana, रसायन is a Sanskrit word, with the literal meaning: Path (āyana) of essence (rasa). It is a term that in early ayurvedic medicine means the science of lengthening lifespan, and in later (post 8th-century) works sometimes refers to Indian alchemy.

The name of the science of Indian alchemy or proto-chemistry, is more generally "The Science of Mercury", or ''Rasaśāstra, रसशास्त्र '' in Sanskrit, Nepali, Marathi, Hindi, Kannada and several other languages. Early Indian alchemical texts discuss the use of prepared forms of mercury or cinnabar (see samskaras). However, there is also ample mention of the preparation of medical tinctures in the early science of Indian alchemy.