In Harry Potter What spell causes fireworks?

Answer 1

Incendio causes regular fire, while Fiendfyre causes a cursed fire to occur (Crabbe uses this in HP 7 in the Room of Requirement as Harry is trying to find Ravenclaw's diadem)
i think there are multiple fire spells. the only ones mentioned in the books are Incendio and Confringo.

*Flagrate and the fiendfyre curse are also fire spells. Dumbledore also uses an unknown spell in HBP to summon a firestorm. Gubraithian fire and the bluebell flames could also be counted. All of these are in the book canon.
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Answer 2

There isn't a specific spell for this, it just happens with bursts of emotion or when they concentrate their magic.

But if you are talking about the film Harry Potter and the Goblet of Fire when he shoots a flare into the sky the spell is 'periculum'.

Answer 3

If you are referring to the fireworks that Fred and George did in Harry Potter and the Order of the Phoenix then it isn't a spell. It is one of their many items that you can buy from their shop, Weasley's Wizard Wheezes. It is called the Basic Blaze Box which which costs 5 gallons and is part of their basic selection called Weasley's wild-fire whiz-bang.

Answer 4

Well, theres Incendio which makes a fire, or there Lumos, that make a light at the end of the wand :)

Answer 5

That's what you call a speciel effect. The attached link might be interesting.