The Half-Blood Prince's Potions Book

• Type: Annotated Textbook
• Owners: Severus Snape (original owner as the Half-Blood Prince), Harry Potter (temporary user)
• Maker: Libatius Borage (author of the original text); Severus Snape (author of the annotations)

The object is a heavily used, tattered, and old copy of the standard Hogwarts sixth-year Potions Textbook, Advanced Potion-Making by Libatius Borage. The cover is peeling, and the pages are stained and filled with dense, spidery, handwritten notes in the margins. These annotations correct the printed instructions, suggest alternative ingredients, and offer more efficient methods for brewing the potions within. Scrawled inside the front cover in the same handwriting is the declaration: “This Book is the Property of the Half-Blood Prince”. Beyond potion-making advice, the book also contains a number of spells seemingly invented by the Prince himself.

The book's value lies not in any inherent enchantment upon the object itself, but in the advanced and often dangerous knowledge inscribed within its pages by its previous owner, the Half-Blood Prince. Its contents can be divided into two main categories:

• Improved Potion-Making Instructions: The Prince's notes offer significant improvements over the official instructions in Advanced Potion-Making. These shortcuts allowed a user to brew potions of a far higher quality than their peers. Notable examples include:
  • Draught of Living Death: The Prince instructs the brewer to crush the Sopophorous bean with the flat side of a silver dagger to release its juice more effectively, rather than cutting it. He also adds a note to stir anticlockwise once for every seven clockwise stirs. This advice allowed Harry Potter to brew a perfect batch and win a bottle of Felix Felicis.
  • Elixir to Induce Euphoria: The Prince's notes suggest adding a sprig of peppermint to counteract the side-effects of occasional singing and nose-tweaking.
• Invented Spells: The book contains several unique and powerful spells created by the Prince, which were not part of the standard Hogwarts curriculum. The spells Harry Potter discovered and used include:
  • Muffliato: A Charm that fills the ears of anyone nearby with an unidentifiable buzzing sound, enabling private conversations.
  • Levicorpus: A nonverbal Jinx that hoists a person into the air by their ankle.
  • Liberacorpus: The nonverbal counter-jinx to `Levicorpus`.
  • Sectumsempra: A powerful and violent Dark Curse that slashes an opponent as if with an invisible sword, causing deep, bleeding gashes. The Prince had noted it was “For Enemies.”

The book was originally owned by Severus Snape during his time as a student at Hogwarts. A gifted Potions student with a Muggle father and a witch mother named Eileen Prince, Snape adopted the moniker of the “Half-Blood Prince” and used this copy of Advanced Potion-Making as a personal diary and experimental workbook. After Snape graduated, the book was left behind in a cupboard in Professor Slughorn's Potions classroom. Years later, when Horace Slughorn returned to teach, Harry Potter arrived at his first N.E.W.T.-level Potions class without a textbook. Slughorn lent him the old, battered copy from the cupboard. Harry used the book's advice throughout his sixth year, excelling in Potions for the first time and becoming a favorite of Slughorn's. This success was instrumental in his winning the Felix Felicis, which he later used to persuade Slughorn to give up a crucial memory concerning Lord Voldemort's Horcruxes. Hermione Granger remained deeply distrustful of the book and its unknown author. After Harry used the `Sectumsempra` curse on Draco Malfoy in a duel, he was horrified by its effects. Under pressure from a furious Snape, Harry hid the book in the Room of Requirement (specifically, its “Room of Hidden Things” configuration), placing it inside a cupboard and marking the location with an old bust wearing a wig and a tarnished Diadem. The identity of the Half-Blood Prince was revealed to be Severus Snape at the end of the year, during the confrontation following the death of Albus Dumbledore. The book was presumably destroyed the following year when Vincent Crabbe unleashed Fiendfyre within the Room of Requirement during the Battle of Hogwarts.

The Half-Blood Prince's book is the central mystery and a primary plot device in Harry Potter and the Half-Blood Prince. It serves as a source of both great success and great conflict for Harry. The knowledge within allows him to obtain the Felix Felicis, a key step in uncovering the secret to defeating Lord Voldemort. Simultaneously, the book drives a wedge between Harry, who comes to idolize the brilliant and creative Prince, and Hermione, who views the unverified, dangerous magic with suspicion. The book's dark spells, particularly `Sectumsempra`, force Harry to confront the darker side of magic and the potential for cruelty in his anonymous mentor. Ultimately, the revelation of the Prince's true identity as Severus Snape provides a stunning twist that deepens the complexity of Snape's character and his long, tortured history.

• In the film adaptation of Harry Potter and the Half-Blood Prince, the handwritten annotations are depicted with a distinct, almost frantic style, visually emphasizing the Prince's obsessive genius (film).
• The discovery of the book in the film happens similarly to the novel, highlighting Harry's choice of the older, more interesting-looking book over a pristine new one (film).