Soot

• Type: Byproduct of Magical Transportation and Communication
• Owners: N/A (Byproduct)
• Maker: N/A (Residue from combustion, particularly from the use of Floo Powder)

Soot is a fine, black or dark-coloured powder consisting of amorphous carbon, produced by the incomplete burning of organic matter. In the wizarding world, it is most notably the messy residue left behind after using the Floo Network. Travellers using Floo Powder are often covered in a layer of soot upon arriving at their destination, which can dirty their clothes, face, and hands. It is a common inconvenience of this form of magical transportation, often requiring the witch or wizard to clean themselves up after a journey.

Soot itself possesses no inherent magical properties. Its significance comes from its direct association with the use of Floo Powder and travel or communication via the Floo Network.

• Byproduct of Travel: It is an unavoidable side effect of travelling through the network of magical fireplaces. The amount of soot may vary, but some level of residue is typical.
• Physical Discomfort: When travelling for the first time, a user might inhale hot ash and soot, leading to coughing and spluttering, as experienced by Harry Potter on his first attempt.
• Indication of Use: The presence of soot in a fireplace or on a person can be a clear indicator that the Floo Network has been recently used.

The presence of soot is a recurring detail associated with nearly every significant use of the Floo Network in the series.

• In Harry Potter and the Chamber of Secrets, Harry Potter uses Floo Powder for the first time to travel from The Burrow to Diagon Alley. He mispronounces his destination and ends up in the fireplace of Borgin and Burkes in Knockturn Alley. He emerges “choking and spluttering, covered in soot,” which forces him to clean himself and his glasses. This dishevelled state allows him to hide and covertly witness Lucius Malfoy and Draco Malfoy in the sinister shop.
• In Harry Potter and the Goblet of Fire, Sirius Black communicates with Harry through the Gryffindor common room fireplace. After Sirius's head disappears from the flames, Harry notes a “faint smell of soot” lingering in the air.
• In Harry Potter and the Deathly Hallows, after escaping from the Ministry of Magic with Salazar Slytherin's Locket, Harry Potter, Ron Weasley, and Hermione Granger use the Floo Network to travel to Grimmauld Place. They tumble out of the drawing-room fireplace “coughing and spluttering, covered in dust and soot.”

Soot primarily serves as a world-building element that adds a layer of realism and consequence to magical transportation. It demonstrates that even in the magical world, powerful methods of travel are not always clean or convenient. Its most crucial plot role is during Harry's first journey to Knockturn Alley. Being covered in soot makes him look out of place and helps him remain inconspicuous while he observes the dark dealings within Borgin and Burkes. This experience provides Harry with his first unfiltered glimpse into the darker side of the wizarding world and the questionable activities of figures like Lucius Malfoy. The physical messiness of the soot reflects the morally messy and dangerous situation Harry has inadvertently stumbled into.