Slughorn's Hourglass was a clock made of two glass vessels connected with a narrow passage through which sand and a green fluid flowed, and green serpentine features adorning the outside. The serpent imagery in its design symbolised Slytherin house, of which Slughorn was the Head. It was kept in Slughorn's Potions Classroom on his desk, though it was presumed to also reside in his office.
The sand ran accordingly with the quality of the conversation: if stimulating, the sand ran slowly.
Horace Slughorn had this hourglass in his possession during the 1996-1997 school year, during which when he explained the properties of the hourglass to Harry Potter the sand ran quickly (as it isn't a very deep conversation) but later as they discussed Lord Voldemort, and what he was like at school, the sand moved so slowly that it seemed to freeze.
Behind the scenes
- This hourglass is never mentioned in the books.
- The sand inside the hourglass seen in the films is white, however the replica hourglass offered by the Noble Collection contains green sand.
- Harry Potter and the Half-Blood Prince (film) (First appearance)
- The Making of Harry Potter (First identified as Slughorn's Hourglass)