Nigredo. An alchemical term, corresponding psychologically to the mental disorientation that typically arises in the process of assimilating unconscious contents, particularly aspects of the shadow.
Self-knowledge is an adventure that carries us unexpectedly far and deep. Even a moderately comprehensive knowledge of the shadow can cause a good deal of confusion and mental darkness, since it gives rise to personality problems which one had never remotely imagined before. For this reason alone we can understand why the alchemists called their nigredo melancholia, “a black blacker than black,” night, an affliction of the soul, confusion, etc., or, more pointedly, the “black raven.” For us the raven seems only a funny allegory, but for the medieval adept it was . . . a well-known allegory of the devil.[The Conjunction,”CW14, par. 741.]