He first recorded these fantasies in his Black Books. He then revised these texts, added reflections on them, and copied them in a calligraphic script into a book entitled Liber Novus bound in red leather, accompanied by his own paintings. It has always been known as the Red Book.
This passage establishes the Red Book’s material origins within Jung’s ‘confrontation with the unconscious’ and its compositional relationship to the Black Books and to the method of active imagination.
, The Red Book: Liber Novus, 2009thesis