Maybe it would be good to mention some of the concepts more important Jungians to be able to capture their interpretation better "psychological" of the Alchemy. In this sense it would be necessary to begin with their wide conception of the human psyche because Jung stops the psyche it is not limited to the Me conscious but to the group formed by the conscience (the conscious being whose axis rector is that Me), the personal unconscious (that lived but submerged in the bottom of the individual psyche) and the collective unconscious that surrounds both for all the sides and that it is constituted by a series of nodules psicoideos to those that called archetypes, which are the relating ones unconscious that modulate the production of symbolic images and even of the behaviors and "behavior rules" more elementary of the human being.
The character that he denominated psicoide of the collective unconscious is one of the keys "iniciatics" of the language críptico of Jung. This great one Swiss hermeneuta understood, with the course of the years that the physical thing and the psychic thing are the two faces of oneself currency that the external thing and the internal thing are deeply tied that "like it is up, it is below" that the spirit and the matter are mated in an unit that the one called psicoidea and that it is not but the "Unus Mundus" of alchemists like Dorneus. And this environment psicoideo that characterizes the collective unconscious, is captured in the human world in a physical and psychic way, in a correlation sincronística with the hermetic maxim that he says "like it is inside it is out."
"Gerardus Dorneus – Jung explains – you see the purpose of the Opus alchemist on one hand in the knowledge of oneself that is at the same time knowledge of God, and on the other hand in the union of the physical body with the one denominated "it united mentalis", which is formed by soul and spirit and he takes place through the knowledge of oneself. Starting from this third level of the Opus he takes place, as him he explains, the "Unus Mundus", the "Ünico World", a preworld or world platonic primordial that it is at the same time the world of the future, or the eternal world" (Carl A. Meier: Wolfgan Pauli and Carl G. Jung. An epistolary exchange. 1932-1958, Editorial alliance).
This perception psicoidea is evidenced in its last works, especially in Mysterium Coniunctionis whose writing took him one decade and that, fortunately, he is translating to Spanish for its publication in book. There it is where Jung highlights that the "Unit of the reality" it is that common background "that is so much physical as psychic and, therefore, none of the two things, but rather a third element, a neuter nature that at most can be captured allusively, because in its nucleus it is momentous", that is to say, metaphysician to use a religious term. As one of their biographers, Gerhard it has pointed out Wehr, it is evidenced in the late work of Jung the great importance that he acquires "all that is not psychic or, more exactly, what is located beyond the psyche and of the matter, what embraces the being’s two environments, and in that way it gathers them" (Carl Gustav Jung. Their life, their work, their influence).
The psicoideo of the archetypes, the "Unus Mundus" and their reflective sincronístic explains, in terms Jungians, the "sympathy" in the answer of the nature to the alchemist’s longing search. But we go for parts to understand it.
The Alchemy, for Jung, era above all a spiritual search in the one that the alchemist, trying to find the mercurial spirit, the "Antrophos", in the elements of the nature (in the matter), it ended up finding it inside itself, and where wanting to redeem to the nature was redeemed itself. According to Jung, "as much in East as in West, the central nucleus of the Alchemy is represented by the doctrine Gnostic of the Anthropos and it is, completely, with arrangement to its essence, one peculiar redemption doctrine" (Symbolism of the Spirit). Not all they achieved it, by no means, because it was easy to be fastened – I eat now – in the great one "the Mayan goddess’s net", that is to say, in the overlaps caused by the psychic projections through which one goes in the other ones, and even in the lively or inanimate, characteristic objects that in fact are not of them but of the personal unconscious of oneself.
The Process of Individuation, name given by Jung to the innate tendency of the human psyche to find their center, their Yes-same one, is a progressive road of self-knowledge, of reveal  of the projections that our personal unconscious emanates in a natural way, what supposes a recovery aware of such projections and, consequently, a gradual bigger knowledge of oneself. And that Process of Individuation bears equally to be aware of the action of the archetypes psicoideos in our life, (the identification, for example, with the Old Sage’s archetype he would make us believe that we are prophets, messiah, an important sabiondillo or something for the style).
This Process of Individuation, in opinion of Jung, is the one that is reflected in the intricate terms alchemists and all its imaginary one symbolic, although it estimated that most of the alchemists ignored the game of projections in which inmersos were and some few ones were only aware of it and they overcame the "net of Mayan."
The archaic psyche, according to Jung, it is fused and identified fully with the nature in a "participation mystique" (as Lévy-Bruhl he called it) due to the entangled net of projections – unconscious, therefore – that link to the external world with the archaic man (the man non rationalist that lasts until the Rebirth, and the man of the primitive tribes). Merced to the Process of Individuation, and after an uninterrupted series of "solve et coagulates" – he disintegrates and it gathers -, the projections go disappearing, one assumes their shades and lights and he submerges, consciously now and endowed with "personality", in the "Unus Mundus", circumstance that he explains why Jung, in its retirement of the tower of Bollingen, spoke to the pans and other objects. It had recovered the "lost unit" and its "I center."

The Nigredo

The first of the stages of the "Opus" alchemist, "Nigredo" or Rot, is the phase of Saturn-Osiris, that of the lead, the immersion in the raw material that, by means of a series of operations, he will transform in "I Pray Filosofal" and in "Philium" or "Lapis Philosophorum" in the last stage, the "Rubedo", after the corresponding combinations among the "it Sulfurates", the "Mercury" and the "Salt."
For Jung this first phase corresponds to the integration of the aspect "dark" of the human psyche, this is, of all those emotions, intuitions, perceptions and thoughts that have been rejected along the life to consider them inappropriate or undesirable defects in living day by day off the with their daily activities (the pragmatic world that the I have been mounted around yes). This supposes a to dive in the personal unconscious and to be aware of the multitude of projections that you/they are spread in people of our surroundings and in objects of our environment, which belong together with that that the I have excluded or rejected for not convenient believe it for him.
On the other hand this phase supposes a to look, face to face, to the somber aspect of the Creation, of included same God…, that is to say, the Wrong, with uppercase. Luz and Darkness are part of the existence in all their environments, and also – to the human eyes – of God. The Alchemy was like a current "underground" and complementary to the medieval and Renaissance dogmatic Christianity, and it opposed to the God of the Good another God "duplex", as the Abraxas Gnostic, in the one that Well and Wrong converged..

The Albedo

The following step is the conscious integration and responsible for the archetype of "that opposed", that is to say, of the "Eternal Feminine" in the case of the man (archetype of the "it Encourages") and of the "Eternal Masculine" in the case of the woman (archetype of the "Animus"). In the literature, for example, the Beatriz of Dante in The Divine Comedy, would be a classic example of this archetypal figure that is the "you/he Encourages."
The human being, so much physical as psychically, it is a conglomerate of opposed. In our genes there are masculine and feminine elements, and another point happens in the psyche. For the man the "it Encourages" it is initially submerged in the personal, confused unconscious and intermingled with the "Shade", but once this has been integrated, the transforms "it Encourages" in a "bridge" that connects us with the psicoideo, with the collective unconscious and their archetypes. It is the element mediator. Now then, like M.L points out. von Franz, "naturally, during this period it also continues the laundry, the calcination, etc, of the "nigredo", because the "Shade" he resembles each other to the hydro of Lerma, with which Hercules fought and to the one that constantly new heads were born instead of the cut ones" ("C.J.Jung… ").
In the psychological plane during the "Albedo" he leaves of the work of moving away the projections that the archetype of the "it Encourages" (I am speaking for men, in this case) it emanates toward the women of our life, from the mother to the sister, to the fiancés, to the wife, to the "star system"…, etc. AND once achieved this initial phase the moment arrives of being faced with the "it Encourages" and to integrate it consciously inside our being, previous overcoming of the problem of the transfer for that which he will be necessary to have very present that the "Dear" where he is it is really inside; he fears that Jung approached mainly in "Psychology of the Transfer" where speaks equally of the paper that carried out the "Soror Mystique" of the alchemist.
In a loving or erotic relationship between man and woman the interpersonal relationships are multiple since besides the relationship among the conscious ego a communication exists at unconscious level in which you/they participate between crossly the Soul and the Animus of both. With the result that, in the Process of Individuation and in the Opus of the Alchemy, one of the serious existent dangers is that of the transfer or, what is worse, the loving passion.
The image of this encounter and dialogue with the Soul are the "conjunction", the hierogamy between the alchemist and its "Soror Mystique", between the King and the Queen of the engravings alchemists, the "chemical wedding of the elements", etc. AND what arises of it is it the Rebis, the "it sews double", the Androgynous one. "Of her the divine son of the philosophers, the terrestrial sun, will arise the luminous and dark center at the same time, the radiant star that reconciles in yes to the Sky and the Earth, the yes and the not, and that it spreads to their surroundings a peace and an extraneous come harmony", it poeticizes the Jungian Etienne Perrot in The on the way to the transformation starting from C.G. Jung and the Alchemy (Edicomunicación), I liberate in the one that Perrot tries to reconcile the thesis Jungians alchemist with that of the occult Tradition. This symbolism is comparable to the one that presents the tantrism, in the one that the two opposed energy currents intersect in the central channel, Sushuma, opening the chakras ("conscientious centers" the called Jung in Miguel’s book Serrano The Hermetic Circle. Letters of two friendships, Jung and Hermann Hesse, Kier), while the man’s semen doesn’t flow toward out, but toward inside, generating a "son of the spirit", as well as it is described in "The Secret of The Corn marigold."
Let us see that that M.L.von Franz says, in "C.G.Jung… ", in this respect: "The participants in the "wedding alchemy" they are almost always described like brother and it mates, mother and son or father and daughter. Their union constitutes an incest then. This incestuous aspect of such a loving constellation has as end the us to make conscious the projection, that is to say: he forces us to realize that, in last term, it is an intimate union of the components of our own personality, of a "spiritual marriage", so that it is not an internal experience projected. To what one mentions it is to an internal unification of the contrary ones in the Yes-same one."

The Rubedo

The last stage of the Alchemy is the "Rubedo" or "Citrinitas", the Work in Red or Golden, where the is reached "diamond body."
In the hermeneutics Jungians the "Rubedo" it is the achievement of the "Entirety", that is to say, the encounter and placement mutual among the Me of our conscious being (that has looked for such "coniunctio"), with the Yes-same one or ME of our total BEING, of which was part (although without knowing it) the Me. It is a new one "conjunction", in which all the opposed ones join and they supplement harmoniously and they are connected directly with the "Unus Mundus", and as such a state it is ineffable, indescribable, it constitutes a Mystery, with the result that the work more important alchemist of Jung is titled Mysterium Coniunctionis. This Yes-same one is the "divine spark" of the one that Eckhart, the Antrophos of the Gnosis, spoke the "interior god" of the mystic, the "Mercury Filosofal" that gathers I get the seemingly more irreconcilable ones opposed, with the result that the alchemists designated him with multiple contrary qualities, and in some texts they designated him, without more rodeos, with same God, but a god "duplex." Another of the names alchemists that had was "Lapis Philosophorum"
"I have called to the Being’s center with the name of Yes-same. Intellectually the Yes-same one is not more than a psychological concept, a term that is good to express the incognizable essence that we can capture as such, since it exceeds, by definition, to our abilities of understanding. "God in us", you he could also call", Jung affirmed in Him me and the unconscious.

Before reaching the plane of the Yes-same one, Jung locates in the one on the way to the Process of Individuation the integration of the archetypes of the "Eternal Boy" and of the "Old Sage", expressed equally in numerous figures alchemists.
"The second step is reached when combining the "it united mentalis", this is, the unit of the spirit and soul, with the body. But an execution of the can only be expected "mysterium coniunctionis" if he has combined the unit of the spirit, soul and body with the "Unus Mundus" of the beginning", Jung would manifest in the second volume of its book Myterium Coniunctionis.
Later, in a letter written to their 82 years, in 1957, he would write: "The transcription of the "conjunction" in human words it is a task that can drive to the doubt, because one is under obligation to find expressions and formulas for a process that takes place "in Mercury" and not in the level of the thought and of the language humans, this is, not in the sphere of the differentiating conscience… The road doesn’t drive on-line straight line forward, for example, from the Earth toward the Sky, or of the matter to the spirit; it is a rather "circumambulatio" and of an approach to the center. We don’t advance leaving a part behind, but fulfilling our task like "mixed composita", this is, as human beings among the opposed ones." This road, if we had to represent it graphically, it would be a hairspring.
To conclude, good it will be to remember these words of Jung in Mysterium Coniunctionis: "I advise to the readers that criticize me to that you/they leave to a side the prejudices that prove the road that I have described, or if not that they suspend their sanity, reason and admit that they don’t understand anything. For thirty years that I study these psychic processes, I have acquired the certainty that the alchemists, as well as the big philosophers of East, refer to such experiences and that, essentially, it is our ignorance of the psyche the one that makes us attribute them the epithet of mystics." Let us remember in this respect that the psyche, for Jung, includes the psicoideo.
On the other hand, Etienne Perrot, notices us the following: "Any psychological description, scientific in the current sense of the word, it will never be able to drain the wealth of the treasure alchemic. Their mission is only to drive to the man toward itself, to allow him to adhere to the universe of symbols in the silence where the being’s weddings processing take place and of these mysterious, terrible and beneficent energy at the same time that Jung designated with the name of archetypes."

Tags: alchemy, archetypes, Jungians