The Revealing Charm makes invisible ink become visible.
References from the canon
- Hermione tried this on Riddle's diary, but it had no apparent effect (CS13).
- "Aparecium" may have been the implied spell in Prisoner of Azkaban when Professor Snape tapped the Marauder's Map with his wand ordering the parchment to "reveal your secrets" before being insulted by the long-ago voices of the Marauders. (PA14)
"appareo" L. to appear