The tradition of alchemy dates back at least to the middle of the first millennium B.C., and probably reaches as far back as prehistoric times. It was, and is, a psychospiritual method whose ultimate aim was the "Great Work," the refining of the base into the noble.
The evolution of the esoteric craft of alchemy appears to be very similar to that of esoteric masonry. In ancient times, skilled groups of artisans were a valuable and elite group of people. Thus the skills involved in working with metals or crafting buildings from stone were essentially "secrets," jealously guarded by their own respective guild. Until the eighteenth century science, craftsmanship and religion were not separated. As these craftsman saw analogies between their craft and the human soul and/or cosmos, initiation into these guilds imparted knowledge and wisdom of both the mundane and the divine. A similar concept is expressed in Oriental philosophy as a Tao (do in Japanese), or a Way of Living. There is the Way of Tea (chaido), the Way of the Sword (kendo), etc. The idea is that every vocation, every Way, is also a way of initiation into the mystery of life.
Like many other esoteric mouth-to-ear teachings, alchemy was generally protected from the profane by secrecy. When it was committed to writing, it was generally done out of fear of the information being lost. Even when this was done, the manuscripts were usually incomplete or had intentional "blinds" to fool the dabbler. This has led many historians to regard alchemists as nothing more than primitive chemists who tried to change lead into gold. Why then, would alchemy persist as a tradition for thousands of years in such widely separated civilizations as those of the Near East and Far East? At a time when many early chemical discoveries were being made, and advanced techniques for the preparation of metals and glass were being implemented, men continued to follow an apparently irrational yet consistent tradition of alchemical processes. It would be foolish, as well as a great insult to the nature of humanity, to state that this tradition had only persisted because men repeatedly fell to the temptation to get rich quickly by creating silver and gold from common metals.
"If alchemy were nothing but a sham, its form of expression would betray arbitrariness and folly at every turn; but in fact it can be seen to possess all the signs of a genuine 'tradition,' that is to say, an organic and consistent... doctrine, and a clear-cut corpus of rules." 
The transmutation of lead into silver or gold does not appear to be possible by ordinary metallurgical processes. In theory, such a change could be possible by manipulation on a molecular or sub-molecular level, possibly through such magickal techniques as vibratory formulae or mantra. However, despite what is theoretically possible, and what a few alchemists such as Nicolas Flamel (1330-1417) seem to claim to have successfully performed, the vast body of alchemical wisdom points to a refining process of the human soul.
At the heart of this wisdom is the analogy to metal-working. The craftsman is identified with the metal to be worked upon. It is said in alchemy that it is the ultimate goal of every metal to be gold. Gold is a manifestation of the essence of the Sun. Lead, the manifestation of the essence of the planet Saturn, is considered to be the starting point of the Work for most men. In order to transmute lead, or any other base metal, into the noble metals of silver and gold, the alchemist must use the formula of "solve et coagula", dissolution and coagulation.
In alchemical symbolism, all metals are considered to be composed of three basic elements; sulphur, salt and quicksilver (mercury). These three elements are often related to the three fundamental tendencies (gunas) in the Hindu system (tamas, sattva, and rajas). Sulphur (spirit) is the active or male principle, Quicksilver (soul) is the receptive or female principle, and Salt (body) is the neutral, static element.
The metal is dissolved into these basic elements (solve) in an oven called an Athanor, from the Arabic at-tannr ("oven"). Sulphur and Quicksilver are, in a certain sense, opposed to one another, but they also long for union. Because of their opposition, they are often depicted in alchemical works as various beasts, often serpents, in combat with one another. It is through this combat and mutual destruction that they recombine in the "chemical marriage" (coagula), and having fought or burned off impurities, a "nobler" metal is created. This process must be repeated several times in order to transmute "lead" into "gold."
When one meditates upon the "chemical marriage," it should be no surprise that Indian alchemists consider it to be a Tantric art. The method of increasing tension and attraction between male and female (Sulphur and Quicksilver) before union, and spiritual revaluation, as described in the foregoing paragraph is a common Tantric practice. In the practice of laya-yoga, meant to arouse the Kundalini, Sulphur and Quicksilver are the Pingal and Id currents which wind themselves around the Merudanda, creating the familiar shape of the caduceus of Hermes.
In recent years, with the revival of magick and breakthroughs in the field of psychology, alchemy has gained much renewed interest. Dr. Carl G. Jung, the prominent psychologist and pioneer in the realm of the subconscious mind, viewed alchemy as an archaic form of psychotherapy, which assisted the craftsman in what he called the "individuation" process, the uniting of conscious and subconscious mind. It should be understood, however, that alchemy, like all forms of occult science, are not "merely" psychological. They deal with not only the conscious and subconscious, but the superconscious or Divine as well.
 Titus Burckhardt, "Alchemy". Penguin Books, Maryland, 1971.