Today (August 23rd) is the date of the festival of Vulcanalia, held in honor of the Roman god of fire and furnace in the ancient Roman world. Centuries later, during the Renaissance, Vulcan became both a popular subject for painters and synonymous with the art of alchemy, but before discussing the Roman god's symbolism in art and alchemy, its useful to remind ourselves of the original myth of Vulcan in the pantheon of Greek-Roman gods..
Vulcan was the son of Jupiter and Juno. As the son of the king and queen of the gods, he should have been handsome, but was ugly as a baby. His mother, Juno was horrified by him. She hurled the tiny baby off the top of Mount Olympus. Vulcan fell down from the sky for a whole day and night, eventually landing in the sea. One of his legs broke when he hit the water and never developed properly. He sank to the depths of the ocean, where the sea-nymph Thetis found him and took him to her underwater grotto, raising him as her own son.
Vulcan had a happy childhood playing with dolphins. When his adopted mother Thetis attended a dinner party held on Mount Olympus wearing a beautiful necklace of silver and sapphires which Vulcan had made for her, Juno asked where she could get such a necklace. Thetis became flustered, which caused Juno to become suspicious; and, at last, she discovered the truth, the baby she had rejected had now grown into a talented blacksmith.
Juno was furious and demanded that Vulcan return home, a demand that he refused. However, he sent her a beautifully constructed chair made of silver and gold. Juno was delighted with this gift but as soon as she sat in it her weight triggered hidden metal bands which sprung forth to hold her fast. The more she struggled the more firmly the mechanical throne gripped her. Juno sat fuming, trapped in Vulcan's chair for three days, unable to sleep or eat. Jupiter finally promised Vulcan that if he released Juno he would give him a wife, Venus the goddess of love and beauty. Vulcan agreed, married Venus and later built a smithy under Mount Etna on the island of Sicily. It was said that whenever Venus was unfaithful, Vulcan grew angry and beat the red-hot metal with such a force that sparks and smoke rose up from the top of the mountain, creating a volcanic eruption. 
During the Renaissance, the subject of Vulcan working at his forge, delivering Achilles armour to Thetis or ensnaring the lovers Venus and Mars, were all popular subjects for artists including Velasquez, Tintoretto, Piero di Cosimo and Rubens, among others, indeed, the Northern Mannerist artist Joachim Wtewael (1566 –1638) painted the dramatic moment of Venus and Mars surprised by Vulcan in no less than three differing versions.(below)
Artists interest in the myth of the lovers Venus and Mars surprised by Vulcan can be interpreted on at least two levels. Firstly, as a commentary upon taboos topics such as sexuality, temptation and adultery in the growing urban population of Europe and secondly, as symbolic of the 'fixing' and union of opposites in the 'Great Work' of alchemy.
It was also during the Renaissance that the physician Paracelsus (1491-1540) introduced the mythological figure of Vulcan as the patron deity of alchemy. To the alchemist/physician Vulcan was synonymous with both the manipulation of fire, heating and distilling of nature's properties for medicine, and the transforming power and creative potential locked within the greater, invisible Man slumbering within; Paracelsus declared-
Alchemy is an art and Vulcan (the governor of fire) is the artist in it. He who is Vulcan has the power of the art ... All things have been created in an unfinished state, nothing is finished, but Vulcan must bring all things to their completion. Everything is at first created in its prima materia, its original stuff; whereupon Vulcan comes, and develops it into its final substance ... God created iron but not that which is to be made of it. He enjoined fire, and Vulcan, who is the lord of fire, to do the rest ... From this it follows that iron must be cleansed of its dross before it can be forged. This process is alchemy; its founder is the smith Vulcan. What is accomplished by fire is alchemy - whether in the furnace or in the kitchen stove. And he who governs fire is Vulcan, even if he be a cook or a man who tends the stove.
Elsewhere Paracelsus writes,
Alchemy is a necessary, indispensable art ... It is an art, and Vulcan is its artist. He who is a Vulcan has mastered this art; he who is not a Vulcan can make no headway in it. 
The British natural philosopher Francis Bacon however, was skeptical of the claims made by Paracelsian alchemists, indignantly exclaiming in his The Advancement of Learning (1605) -
Abandoning Minerva and wisdom they play court to the sooty smith Vulcan and his pots and pans.
Nevertheless, Paracelsian alchemists including the foremost promoter of Paracelsian alchemy Gerard Dorn, the early Belgian scientist Jan Baptist van Helmont, and Arthur Dee, the eldest son of the magus John Dee, all acknowledged the Roman god of forge and furnace as symbolic of their art. Arthur Dee in his Arca Arcarnum mysteriously stated -
'Though I am constrained to die and be buried nevertheless Vulcan carefully gives me birth'.
The Paracelsian ‘deity’ associated with alchemy features no less than three times in Sir Thomas Browne’s hermetic discourse The Garden of Cyrus (1658). Firstly, in the very opening sentence of the discourse -
That Vulcan gave arrows unto Apollo and Diana according to gentile theology in the work of the fourth day may pass for no blind apprehension of the creation of the Sun and Moon.
Secondly, within the context of Classical myth in which Vulcan constructs and casts an invisible network ensnaring the lovers Venus and Mars caught in bed inflagrante delicato -
As for that famous network of Vulcan, which enclosed Mars and Venus, and caused that inextinguishable laugh in heaven; since the gods themselves could not discern it, we shall not pry into it. Although why Vulcan bound them, Neptune loosed them, and Apollo should first discover them, might afford no vulgar mythology.
Lastly, at the apotheosis of his literary-alchemical opus, Browne specifies the three factors necessary for determining truth, namely authority, reason and experience; Vulcan here representing the "higher man" who, not unlike the Gnostic, "Man of Light," uses his craftsmanship and skills to aid, enlighten and liberate the Spiritual Man within.
Flat and Flexible truths are beat out by every hammer, but Vulcan and his whole forge sweat to work out Achilles his armour.
In his late work Christian Morals which was written as a parental 'advisio' for his grown-up children, Sir Thomas Browne alludes a further three times to Vulcan, and just as the Belgian scientist Van Helmont (1580-1644) before him defined alchemy as Vulcan's art. In a passage which perceptively describes the human psyche as 'the theatre of ourselves', Browne somewhat critically stated-
'Vulcan's Art doth nothing doth nothing in this internal militia; wherein not the armour of Achilles, but the armature of St. Paul, gives the glorious day,
In modern times the Swiss psychologist Carl Jung interpreted Vulcan as one who:
kindles the fiery wheel of the essence in the soul when it 'breaks off' from God; whence come desire and sin, which are the "wrath of God." 
The alchemists adoption of the mythical figure of Vulcan may be interpreted on several levels. At the lowest scale of interpretation Vulcan represents the cunning amoral demi-urge who blindly gains power over Nature without integrity; this mundane level anticipates the nascent Industrial Revolution of the 18th and 19th centuries. The activities of extracting coal from mines to fuel colossal furnaces to manufacture steel and iron on a gigantic scale, and the subsequent development of the railroad and train throughout Europe and North America are distinctly Vulcan-like activities; as is the general "busyness" of the Protestant work-ethic of industrialised Western society also strongly reflected in this archetypal figure.
The transformative power of Vulcan the "higher man" and anthropos figure of the alchemists has today devolved into the negative aspects of a demi-urge figure; none other than modern technological man, who, divorced from God, forges his own destiny, independent of Religion, Divine Love or theological considerations, towards a brave new world or utopia. This is reflected in the fact that today the name of Vulcan is best known as either the name of a bomber plane or as the extra-terrestrial semi-human species as represented by Mr. Spock in the American science-fiction TV and film series 'Star-Trek'.
At a higher level of interpretation however, Vulcan is transformed to become an inspired visionary who is capable of releasing Mankind from the bonds of unknowingness and darkness; which is how alchemists such as Paracelsus and followers such as Van Helmont, Arthur Dee and Sir Thomas Browne interpreted the symbolism of Vulcan.
This article was originally written for Wikipedia in 2003 and subsequently duplicated in various places elsewhere on-line before its eventual deletion.
I assert the right to be identified as the original author of this short essay.
Other on-line writings encountered on thus subject of Vulcan and his relationship to alchemy are mirror duplication from the Wikipedia original, and the product of copy and paste scholarship.
As Sir Thomas Browne once stated -
'Men are still content to plume themselves in other’s feathers’.
Art-work (top) Vulcan at forge by Chris Appel
Next - One of three canvases painted by the Northern Mannerist artist, Joachim Wtewael of Venus and Mars surprised by Vulcan
Last- Tintoretto - Venus and Mars surprised by Vulcan
 Abridged from Wikipedia
 Paracelsus Selected writings ed. Jolandi Jacobi Princeton 1951
 CW 12 215
 Christian Morals Part II Section 9 pub. post. 1716