waidan

thumb|Woodblock printing#China|Chinese woodblock illustration of a waidan alchemical refining furnace, 1856 (Illustrated Manual of External Medicine)

''', translated as 'external alchemy'''' or 'external elixir', is the early branch of Chinese alchemy that focuses upon compounding elixirs of immortality by heating minerals, metals, and other natural substances in a luted crucible. The later branch of esoteric neidan 'inner alchemy', which borrowed doctrines and vocabulary from exoteric , is based on allegorically producing elixirs within the endocrine or hormonal system of the practitioner's body, through Daoist meditation, diet, and physiological practices. The practice of external alchemy originated in the early Han dynasty (206 BCE–220 CE), grew in popularity until the Tang (618–907), when began and several emperors died from alchemical elixir poisoning, and gradually declined until the Ming dynasty (1368–1644).