How do they make fireworks explode in specific shapes?

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I was at an event with a giant, choreographed firework show. Like they literally brought in Japanese masters of pyrotechnics for it. It was beautiful and all kinds of shapes like flowers and hearts and stuff.

And afaik they do different colours by burning different elements but how do they do specific shapes and like timings? Like one piece of firework having several different layers and colours and stuff. How does it not all explode at the same time in all kinds of directions?

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