Vampiric Ink
Despite its ominous name, vampiric ink shares only one trait with the foul undead – it too cannot stand the light of the sun, vampiric ink appears to be normal and unremarkable black ink.
Ultimate Equipment Guide II
Author Greg Lynch, J. C. Alvarez
Publisher Mongoose Publishing
Publish date 2005
Vampiric ink is based on burning ink. Unlike burning ink, however, vampiric ink is invisible until triggered. It does not require an alchemical powder or a mirror to trigger it, however. Simple exposure to direct sunlight is all that is required to make vampiric ink appear. Immediately upon exposure to direct sunlight, the hidden words spring into visibility, glowing brightly.
However, they do not last long, as two rounds after the ink is exposed, it bursts into flame, destroying the message. The fire of vampiric ink burns hotter than normal burning ink, and will either destroy or badly char any flammable substance the words happen to be written on. For example, a sheet of paper will be destroyed, while a wooden plank would be badly charred. In the case of the latter, the charring is too extensive to retain any sign of the message. Anyone holding an item written in vampiric ink when the ink ignites will take 1d4 points of damage from the sudden fire.
Vampiric ink is only triggered by direct exposure to sunlight. A piece of paper bearing a message written in vampiric ink could be folded in half to protect the message from the sun.
Ink, Vampiric (1 oz. phial): 40 gp