Jacques Herbin Glow in the dark Phosphorescent Ink

even*cleveland

“Extremely fun addition to the art supply stash—you apply it with a brush or a dip pen, and it goes on invisible, but pops in the dark or under UV, making it the perfect medium for for secret messages. And Napoleon used Herbin inks, too (they've been making inks since the 1600s), possibly for his secret messages.”