Medieval literature
The albedo is the second stage of alchemy. In this process, the subject is divided into two opposing principles to be later coagulated to form a unity of opposites or "coincidentia oppositorum" during rubedo. Alchemists also applied it to an individual's soul after the first phase is completed, which entailed the decay of matter. In Medieval literature, which developed an intricate system of images and symbols for alchemy, the dove often represented this stage while the raven symbolized nigredo.