The most clear reflection of this is in some of his word choices... using "kia" for eye (in Sanskrit, the word's "khya"), "ikkha" for will (in Sanskrit, Iccha), etc. These terms are used in Tantra quite frequently... especially "khya", which is an unusual, almost fundamentally Tantric, use of the word.
Some of his workings also bring to mind Tantric works... such as having sex with 18 prostitutes in a single night which, in turn, unleashed a great burst of creativity. This is very commensurate with Tantric practice in general (using sexual energy to boost kundalini-shakti up the susumna), and in fact it's very nearly impossible to have sex 18 times in a single night if one ejaculates each, or even most, times (talk about sore, eh? :)
My suspicion, though it's never explicitly stated, is that he re-channeled the stored semen (bija or rasa in Tantra) into a "higher energy"... in this case, artistic creativity. Again, quite in keeping with Tantric practice generally.
Spare's great attraction to ugly, even deformed, women in the course of his work also reflects on Tantric involvement; in most forms of Tantra, one unites specifically with things that disgust one in order to overcome the limitations that such disgust imposes upon them. This is especially noteable amongst Tantric groups like the Ahoras and Kapilikas, who were known for mutilating themselves and for dining on such delicacies as rotting human corpses and feces. In fact, this is a major element of the practice of such groups.
Spare makes reference to Kia as "the supreme bliss" in his work... considering that he was almost completely visually oriented, the eye was, to him, exactly that. And he does equate, in fact, Kia with the eye in his famous formula of "uniting the hand (ikkha/iccha) with the eye (kia/khia)". Look, especially, at "A Creed of Despair" in Spare's "Earth Inferno":
"My ambition is DEAD,This piece could have been lifted DIRECTLY from any number of Tantric doctrines. Especially, note the peculiar way in which "kia" is spelled here... in exactly the way that translators at the time (and to this day) transliterate Sanskrit words, to indicate that the final "a" is pronounced.
Died premature and with it the love of care,
Also the Jewel in the Lotus.
The morrow holds nought
Save Sin and Death.
I am even exempt from my own created PLEASURES ---
The barrenness of this life but remains.
Yet in despair we begin to see true light. AMEN.
In weakness we can become strong.
Revere the Kiā and Your Mind will become TRANQUIL."
And "the jewel in the lotus"... again, a Tantric (albeit Buddhist tantric) formula, which means "Om". The inlcusion of "om" in every mantra is not a specifically Tantric theme; indeed, many Tantrics rebelled against it as being part of the very Brahminic tradition which Tantric was formulated against. And, also, Tantra advises withdrawal from the perceived obligations of this world and the eschewing of discursive thought revolving around pain and pleasure.
So, in reducing this formula, we get:
"I give up my drive for worldly things,All of this is quite in keeping with Tantric thought and practice!
Though young, I care no longer for obligations of this world,
And I rebuke religion and priests.
Tomorrow is nothing
And the desire for it is corruption.
I no longer have pleasures, nor pains.
My body is but a shell, empty of meaning.
By renunciation, I perceive my truth... my vision of god.
By weakening my body (Spare was certainly an ascetic!), I strengthen my spirit.
Revere sight for sight's sake, without discrimination (Kiā is not a discriminative function, and the eye is not a discriminative organ) and you will have peace."
Now, if you have Earth Inferno, take a look at the accompanying illustration entitled "The Despair"....
Note the strange position of the woman in black, her arms crossed behind her back? The woman stretched out upon the altar? The little masked man squatting next to her? And note one more thing... Spare was a master draughtsman, and yet there appears to be an error in the positioning of the figures... the woman in black's legs vanish through the floor or altar upon which the sacrifice is stretched.
The woman in black is a Tantric goddess... there is even, if you look closely, a snake crawling up her chest from between her cleavage. You can just see it's head peeking above the top of her low-cut dress, just between her breasts. That snake is Kundalini, and identifies the woman with Shakti herself. Note, too, that she stands *to the left* of the figure that (I think) is supposed to be Spare himself... that's absolutely typical Tantric iconography. Note, further, that the Woman in Black appears to need a shave!!!! And, oddly enough, so does the figure of Spare. In other words, they participate in one being... the woman is herself a part of Spare in a way... being his own kundalini-shakti. The use of three candles is significant in that one name y which this very goddess is known is Tripura... literally "three cities", the three cities being the three gunas (attributes) that, according to Tantric thought, make up all creation... tamas (darkness/matter), rajas (fire/passion) and Sattva (brilliants/divinity).
The Tantric elements in just this one illustration (drawn in 1905) indicate strongly a Tantric connection... and considering Spare's magickal tutor was an old woman (I think, perhaps, a Yogini herself, though she's left no written record), I think that the Tantric element may have been the origin of much of Spare's work, both magically and artistically.
However, remember that secrecy is considered by most Tantric practitioners to be the very essence of Tantra... he's not going to come out and tell you that he's based much of his work on Tantra. However, I think Kenneth Grant knows about this connection. There are many other instances and examples of this tie-in as well, and I've even been offered anecdotal evidence in the past that Spare, in fact, actively studied Tantra at a later point in his life. But my fingers are getting tired...