The alchemists say that nigredo lasts forty days. Forty days has a symbolic value. Jesus fasted for forty days in the desert. There are forty days of fasting between Easter and Ascension Day. The Israelites wandered for forty days in the desert. Saint Antonius spent forty years in the Sahara desert, being plagued by visions of extreme erotic scenes and devils.
Psychologically, nigredo is a process of directing oneself to find self-knowledge. A problem is given full attention and reduced to its core. This is not done so much in an intellectual way, but especially by feeling the emotions. By really going into to it, one causes putrefaction, the decomposition of that in which one had been stuck. The confrontation with the inner reality is often painful, and can lead to depression. But once in the depth of the darkness, with the discovery of the seed of the problem, the seed in the ‘prima materia’, the white light is born (=albedo, whiteness, the next phase). A state of rest arises. Insight into the problem has been gained, it has been worked out emotionally, and knowledge arises on how to handle it in a more positive way and to build a more pure attitude.
http://www.soul-guidance.com/houseofthesun/alchemy%202.htm
