How do fireworks work?
(Lansing State Journal, July 17, 1996)
Fireworks can be thought of as two-stage rockets. The first stage is made of gun powder, another Chinese invention. Burning the gun powder produces a stream of hot gases that escape from the bottom, through a small hole.
These hot gases push against the ground to send the fireworks high into the sky. Once the first stage is done burning then the second stage begins to burn.
The second stage is a sealed compartment so that the hot gases have nowhere to escape. In addition to gun powder, the second stage contains an oxidizing agent.
These chemicals produce oxygen to speed up the burning. Pressure builds up until the fireworks blows up causing the loud bang that you hear.
The second stage also contains various metals which cause different colored sparks to shoot out when the firework explodes.
This doesn’t explain how all of the neat shapes are created; but that is part of the secret art of fireworks.
It is worth noting that the extreme heat and explosive power of an exploding firework make fireworks very dangerous for untrained personnel.