the wingless bird, the red sulphur, is an underlying factor of the inner psychic life and is always what one has first to unearth, for it is the prima materia.
Von Franz identifies red sulphur as the irreducible prima materia of psychic work — the instinctive, drive-laden understructure that must be encountered before any transformation is possible.
, Alchemy: An Introduction to the Symbolism and the Psychology, 1980thesis