These color terms describe: (1) stages of the work; (2) conditions of the material worked on; and (3) states in the psyche of the artifex or worker-alchemist. Each color term combines three distinct categories which our modern consciousness keeps separate: the method of working, the stuff worked on, and the condition of the worker. For our epistemology, there is no inherent or necessary relation among method, problem, and subjectivity. For example, for any alchemical substance to enter the nigredo phase and blacken, the operations must be dark and are called, in alchemical language, mortificatio, putrefactio, calcinatio. and iteratio. That is, the modus operandi is slow, repetitive, difficult, desiccating, severe, astringent, effortful, coagulating, and/or pulverizing. All the while, the worker enters a nigredo state: depressed, confused, constricted, anguished, and subject to pessimistic, even paranoid, thoughts of sickness, failure, and death. The alchemical mode of science maintained the law of similitudes among all participants in any activity: the work, the way of working and the worker. All must conform; whereas in science the subjectivity of the experimenter may be radically separated from the experimental design and from the materials of the experiment. Alchemical method, by contrast, treats each problem according both to its and the alchemist's nature. That is why no comprehensive system can be drawn from alchemical texts; why measurement plays an indifferent role; why the inventions of each alchemist are stridently opposed by other alchemists; and why even the materials worked on are so radically differentiated - so many kinds of salt, so many names for mercury, so many styles and shapes of instruments. The radical idiosyncrasy of, and yet deep concordance among, method, problem, and subjectivity also account for why depth psychology finds alchemy so useful a background for the work in its laboratories: the consulting rooms where nigredo conditions are all too familiar.
— James Hillman
Modern epistemology is built on the clean separation Hillman is pointing at here: the scientist's inner weather is noise, to be filtered out so the method can proceed uncontaminated. Alchemy refused this. It insisted that the blackening of the material and the blackening of the worker are the same event — not causally linked, not metaphorically parallel, but structurally identical under the law of similitudes. When the substance enters nigredo, the alchemist enters it too. There is no position outside the work from which to observe it neutrally.
What this means for the consulting room — or for anyone sitting with genuine psychic darkness — is that the depression, the confusion, the paranoid drift toward thoughts of failure and death are not interruptions of the work. They are the work. The mortificatio is not happening to the soul despite the process; it is the process, operating simultaneously at every level. This is what modern frameworks consistently get wrong when they treat the therapist's countertransference as interference, or when a person in depression treats their own anguish as a malfunction to be corrected rather than as the specific logic of what they are in the middle of. Hillman's point is structural: you cannot have nigredo in the material and keep the worker in some other, brighter phase. The concordance is not optional.
James Hillman·Alchemical Psychology·2010