The Great Work (Latin: Magnum opus) is an alchemical term for the process of working with the prima materia to create the philosopher's stone. It has been used to describe personal and spiritual transmutation in the Hermetic tradition, attached to laboratory processes and chemical color changes, used as a model for the individuation process, and as a device in art and literature. The magnum opus has been carried forward in new age and neo-hermetic movements which sometimes attached new symbolism and significance to the processes. It originally had four stages:

• nigredo, a blackening or melanosis
• albedo, a whitening or leucosis
• citrinitas, a yellowing or xanthosis
• rubedo, a reddening, purpling, or iosis