In occultism, Pact ink is the specially prepared ink that a contract with the devil must be written in, otherwise the contract is invalid. Various recipes exist. Detailed instructions are rare. The basic recipe is the same as that for Iron gall ink.
Pact Ink for Devils and Spirits (14th century)
- Gall nuts - 10 ounces (280 g)
- Roman Vitriol or Green Copperas (ferrous sulphate) - 3 ounces (85 g)
- Rock alum - 3 ounces (85 g)
- Gum arabic - 3 ounces (85 g) 
- Spelker, Rich (1999-11-19). "Iron Gall Ink & Permanence". Retrieved 2008-09-19.
- Waite, Arthur Edward (1972). The Book of Black Magic: Including the Rites and Mysteries of Goëtic Theurgy, Sorcery, and Infernal Necromancy. Red Wheel. p. 161. ISBN 0-87728-207-2.