"...we have achieved correct identification of the potion's ingredients by Scarpin's Revelaspell..."
-- Horace Slughorn (HBP18)
Used to identify the ingredients of the target potion or the enchantments on a target object.
References from the canon
Similar to Snape's "Reveal your secret" and "Show yourself" that he pronounced over the Marauder's Map (PA14). After the trouble with Tom Riddle's Diary the year before, he was just as suspicious of the Map as Hermione was about the Half-Blood Prince copy of Advanced Potion Making.