Diagrams accompanied by letters and a few words are credited with magical powers, but still tantric spells are things to be recited rather than written.
"Hinduism and Buddhism, Vol I. (of 3) An Historical Sketch"
Charles Eliot
But many of the works mentioned sound like late tantric texts rather than compositions of the early heretics to whom they are attributed.
"Hinduism and Buddhism, Vol I. (of 3) An Historical Sketch"
Charles Eliot
It may also place itself en rapport with a spiritual or elemental existence by evoking it, and concentrating its attention and regard upon it for purposes of black magic and tantric worship.
"The Best Psychic Stories"
Various