In 1928, Carl Jung painted a mandala with a golden castle at its center. Shortly afterward the sinologist Richard Wilhelm sent him the text of a Chinese alchemical treatise, The Secret of the Golden Flower, and the painting stopped looking like a private oddity.
Jung, then in his fifties and famous, spent roughly the next three decades reading the most ridiculed literature in European history. The result was three enormous books, a theory that reshaped how the public imagines alchemy, and an argument with historians that is still going.
The text that ended the Red Book
For more than a decade before Wilhelm's package arrived, Jung had been recording and illustrating his own visions in the private volume now known as the Red Book. He never finished it. In an afterword written in 1959 he explained why: "The beginning of the end came in 1928," he wrote, naming Wilhelm's text as the cause.
What the Chinese treatise gave him was company. Here was a centuries-old tradition describing an inner process, in images of light, circulation and a golden center, that resembled what he and his patients had been producing spontaneously. He described it as the first event that broke through his isolation. The Philemon Foundation, which edits Jung's unpublished papers, treats the 1929 collaboration with Wilhelm as the hinge of his career: the end of the private experiment and the start of a comparative project carried out through other people's texts.
From China he turned to Europe. If Taoist alchemy described psychic transformation, perhaps the Latin alchemists, with their kings, dragons, sealed vessels and chemical weddings, had been doing the same.
Building the case
It was slow work. Jung collected rare alchemical books and manuscripts, and lectured on the subject at the Eranos conferences in 1935 and 1936. The Philemon Foundation notes that he also drafted a major monograph on alchemy and individuation around 1937, then shelved it, explaining in 1941 that the subject had turned out to be much vaster than his limited knowledge.
Psychology and Alchemy finally appeared in 1944, built on the reworked Eranos lectures. The Princeton edition carries 270 illustrations, many drawn from Jung's own collection. Its second part analyzes a long series of dreams from a modern scientist with no knowledge of alchemy, whose imagery kept arriving at alchemical motifs on its own. Jung kept the dreamer anonymous. He was the physicist Wolfgang Pauli, who recorded more than 400 dreams while working with one of Jung's assistants.
The capstone came a decade later. Mysterium Coniunctionis, on the union of opposites in alchemy and psychology, was published in 1955 and 1956 and completed, his publisher notes, in his 81st year. It was his last major work.
The projection thesis
Jung's argument can be stated in a sentence. The alchemists, working before chemistry had sorted out what matter was, did not clearly separate what was happening in the flask from what was happening in themselves, and so they saw their own unconscious processes in the vessel. Of the alchemist he wrote that "he projected the unconscious into the darkness of matter in order to illuminate it."
On this reading the famous stages of the work, the blackening, the whitening, the reddening, are a map of psychological development that Jung called individuation. The philosopher's stone is a symbol of the integrated self. Alchemical texts seem deranged as chemistry, on this view, because they are not at bottom about chemistry.
He was not the first to suggest it. Ethan Allen Hitchcock and Herbert Silberer had each read alchemy as inner work before him. But Jung had the fame and the pictures. Historians of science noticed early (the journal Isis ran an assessment by Walter Pagel titled "Jung's Views on Alchemy" in 1948), and for decades his interpretation was the default one for educated readers.
What the historians found in the flask
Beginning in the 1990s, two historians of science, William R. Newman and Lawrence M. Principe, went after that default. In papers published in 1998 and 2001, the second titled "Some Problems with the Historiography of Alchemy," they made three linked claims.
First, in the seventeenth century there was no real distinction between alchemy and chemistry. Newman and Principe proposed the period term "chymistry" to cover the whole undivided enterprise.
Second, the strange language was a code, not a dream. Alchemists used cover names, or Decknamen, to protect trade secrets, and those names can often be translated back into specific substances and operations. Newman devoted a 1996 article to exactly this point, testing Jung against the writings of the alchemist known as Eirenaeus Philalethes. Principe then did what Jung never tried: he went into the lab. A 2014 review in Medical History of his book The Secrets of Alchemy describes him decoding symbolic descriptions and replicating the experiments with his own hands, showing that seemingly nonsensical texts record what really happened at the furnace.
Third, the notion of a purely spiritual alchemy is recent. Newman and Principe trace it to nineteenth-century occultists such as Mary Anne Atwood, Hitchcock and A. E. Waite, and argue that Jung inherited a Victorian fashion and mistook it for the Middle Ages.
Not quite settled. The critique landed hard and has reshaped the field. A dragon devouring its tail may well be a distillation.
But the rebuttals have substance too. In a 2010 survey of the controversy, the scholar George-Florin Calian pointed out that the division of alchemy into a practical and a speculative branch is not a Victorian invention. Roger Bacon drew it in 1267. Calian also argued that figures such as Michael Maier and Jakob Böhme cannot plausibly be reduced to bench chemists, and that Jung never actually denied alchemy's laboratory side. The historian Hereward Tilton has charged Newman and Principe with factual and methodological errors of their own.
As history, Jung's thesis overreaches: the alchemists knew a great deal about what was in the flask, and wrote in riddles on purpose. As psychology, his use of their imagery stands or falls on separate grounds.
The real legacy
A leading psychiatrist staked the last third of his working life on the hunch that a discarded science still had something to say. He was right about that, even where he was wrong about what it said.
Alchemy is studied seriously today partly because Jung made it interesting and partly because Newman and Principe made it legible. The psychologist rescued the symbols. The historians rescued the chemistry. The alchemists, who never saw a contradiction between the two, would probably be amused that it took so long.