How Do Fireworks Work, Really?

Written by Sarah Dobbs

Every year, as the Fourth of July nears, the familiar sound of explosions fills the air. Fireworks have been around for over a thousand years in various forms and show no sign of disappearing anytime soon. But have you ever wondered how they actually work? Most people know to light the fuse and step back. Let’s dive deeper...

ROCKETS

Rocket-style fireworks can create a variety of effects when they explode, but the basic components of an aerial firework are fairly consistent. Each rocket contains several key parts: a mortar, fuses, propellant powder, a shell, a bursting charge, and a collection of 'stars.' The mortar serves as the outer casing, and the fuse is the part you light. As the fuse burns, the propellant ignites, sending the firework soaring into the sky.

Once it’s in the air, a time delay fuse inside the shell ignites a second explosion. This triggers the bursting charge, which detonates the stars—tiny explosive pellets made of fuel and metallic compounds that produce the colorful effects in the display. Different metals produce different hues when ignited: barium creates green, calcium salts turn orange, magnesium burns white, copper makes blue, lithium results in red, and sodium gives off a golden glow. The arrangement of the stars determines the shape of the explosion—so, for instance, if they’re arranged in a heart shape, the explosion will reflect that shape in the sky.

Additional effects can be incorporated by mixing in various ingredients; certain fuels can create sound effects, like the whistling or screaming noises some rockets emit as they ascend. Stars can also be layered with different metallic compounds to create multicolored explosions. Some fireworks even feature multiple stages of explosions, with multiple fuses inside the shell. As each fuse burns, a new explosive goes off, creating a more complex display.

FOUNTAINS

Not all fireworks are designed to shoot into the sky and explode. Fountains, for instance, remain on the ground and typically don't go off with a bang. Instead, they stay in place, releasing a beautiful cascade of sparks—similar to a fountain, but with pyrotechnic effects rather than water.

Fountains are typically cone-shaped and are made from a paper or plastic tube with clay plugs sealing both ends. Inside the tube, various types of fuel and metal compounds are stored to create the sparkling effects. When the fuse is lit, the fuel ignites, and the sparks are expelled through an opening at the top of the fountain.

Like other fireworks, different metals produce distinct colors and effects. Multi-stage displays can be created by grouping several tubes together, so as one completes its sequence, the next begins, introducing different colors or sounds to the show.

CATHERINE WHEELS

Catherine wheels are another popular type of firework, created using similar ingredients but resulting in a distinct effect. Named after the unfortunate Saint Catherine, these fireworks are typically attached to a pole or mount, allowing them to spin as they burn and produce a spiral of sparks.

Larger Catherine wheels often feature a plastic disk at their center, surrounded by 'gerbs' attached along the edge. The gerbs are akin to fountains, containing tubes filled with a mixture of ingredients that generate the desired effects. When ignited, the explosive thrust causes the wheel to spin while it burns. As with other fireworks, the display can be made more intricate by adding multi-stage effects and varying colors, with each gerb igniting sequentially to alter the wheel’s appearance.

Smaller Catherine wheels, on the other hand, might consist of a single long, thin tube coiled around a smaller central disk. The ignition thrust still causes the wheel to spin as it burns.

SPARKLERS

The only firework that’s safe to hold in your hand once lit is a sparkler—an essential part of any Fourth of July celebration. Unlike other fireworks that go off with a bang, sparklers burn slowly, producing a steady stream of sparks for about a minute, trailing down a metal wire. They’re pretty straightforward: the metal wire is coated in a pyrotechnic compound made up of a metallic fuel, an oxidizer, and a binder.

The metallic fuel is responsible for creating the sparks; it’s typically aluminum or magnesium, which give off white sparks, though some sparklers may use iron or ferrotitanium to create gold sparks instead. The oxidizer, usually potassium nitrate, supplies the oxygen to keep the spark burning. A flammable starch serves as the binding agent, holding everything together and burning away once the sparkler is lit.

Hopefully, none of this has ruined the wonder of a fireworks display for you. If anything, next time you see a green firework, you’ll impress your friends by casually saying, 'oooh, barium.'