How Do Fireworks Explode?

The fuse sets of a charge that ignites the gunpowder, that propels the firework into the sky. Once the firework is in the sky, the gunpowder in the firework ignites. This causes the explosions or "stars". They contain metal salts and iron fillings, which explode into the bright sparkles that you see in the sky. Most big fireworks have automatic timers for when they go off.