The colour stages of the Great Work

The Great Work is conventionally divided into colour stages: nigredo (the blackening), albedo (the whitening), citrinitas (the yellowing) and rubedo (the reddening), though the yellow stage is often omitted in later accounts, leaving a three-fold black-white-red sequence. The stages describe the changing appearance of the matter in the alchemist's vessel as the work proceeds toward the Philosophers' Stone.

Nigredo is the initial breakdown and putrefaction, a dissolution into blackness; albedo the purification and washing that follows; citrinitas the dawning of a golden light; rubedo the final reddening in which the Stone is achieved.