How Do Fireworks...Work?

By Jamie Condliffe on at

Remember, remember, the fifth of November. Let’s face it, though, most of us don’t bother to remember the Gunpowder Plot these days, but focus on the fireworks instead. Lots of fireworks. Lots and lots and lots of them. But they're hardly rocket science, right? Uh, wrong.

You might be surprised by just how much science is actually stuffed into the little guys. The good news is that most fireworks -- from huge skyrockets to crappy roman candles -- work in pretty much the same way, so once you understand how one works, the rest is child's play. Not that we condone children playing with fireworks.

So, first things first: just how do they create such beautiful bursts of colour as opposed to a huge exploding mess?


Stars In Your Eyes

In the fireworks biz, those little coloured bursts that light up the sky are called stars -- and they’re not as haphazard as they look. They’re carefully-crafted lumps of explosive good: tiny pellets that produce an intense light when they burn. Each of those stars is made up of a mixture of fuel in the form of sulphur or charcoal; an accelerant that makes the fuel burn harder, and specially chosen colour-producing chemicals, all held together in tiny lumps using a binder. By tweaking the concentrations of the ingredients, the stars can be tuned to be brighter or dimmer, or burn out faster or slower.

The colour of the star depends on the chemicals that are thrown into the mix. In fact, if you cast your mind back to chemistry class, when you used to shove whatever you could lay your hands on in the Bunsen burner -- and I don’t for one minute believe you if you never melted your Helix ruler over the flame -- you might recall that different metals burn different colours. Strontium burns intense red; sodium burns yellow. Barium’s flame is green, and copper’s blue. All you have to do is choose the correct metal to colour your firework’s stars with! It’s even possible to make stars that change colour, using an outer layer that contains one metal and an inner core that contains another. The brightest stars, called Mag Stars, are fueled by aluminium, which produces a clear, brilliant white light -- magnesium, from where they get their name, is now too expensive.


Throw Some Shapes

So, that’s the colour sorted, but how the hell do you get fireworks to make such beautiful shapes? It’s down to two factors: timing, and how the stars are packed in. When a firework’s shell is launched into the air the fuse is burning and with any luck -- or, y’know, through some careful calculations, whatever -- it’s just the right length to ignite the explosive charge at the desired altitude. When the charge explodes, it ignites a stash of gunpowder, making the big bang we’re all familiar with (no, not that Big Bang, doofus). It’s that explosion which ignites the stars and throws them outwards in all directions.

But the so-clever-yet-so-simple part is how the stars then make their wonderful shapes. Basically, sheets of card or paper have the stars fixed to them in precise arrangements. Those pieces of card are then stacked on top of each other like Post-it notes and placed above the explosive part of the rocket. When the explosion goes off, the pellets are ignited, and hopefully propelled at equal speeds in all directions, so they spread out in the same pattern as they were arranged in on the piece of paper. Careful placement of the stars means you can create any design you want. Our favourite, however, is the world’s most recognisable emoticon, in firework form: the smiley face.


You Spin Me Right Round, Baby

But even geekier than emoticon fireworks is the Catherine wheel, if only because it makes it socially acceptable to discuss rotational dynamics. It’s rather blood-thirstily named after the good ol’fashioned instrument of torture on which St. Catherine was martyred. (I’ve left out the details as it’s pretty grizzly and involves big hammers; broken bones and rotting corpses, but the Wikipedia article does a very thorough job of describing the process. You know, just in case you’re interested.)

The (slightly) less lethal Catherine wheels we love today are made up of a spiral-shaped firework, with a pin at its centre. When it’s lit, the thrust of the firework causes it to rotate, producing a circle of sparks and coloured flame. As it burns, its weight drops but the force it generates stays just about constant, so it gradually gets faster and faster and faster... until it whimpers out and rattles to a disappointing stop.

Less disappointing, though, is the fact that the word’s biggest Catherine wheel was a staggering 105 ft in diameter (you can watch it in action here), which is about as tall as an eight story building, and almost as dangerous as waking up your partner using fireworks. Maybe health and safety laws aren’t so tight in Malta.

All of which is, of course, very interesting, but doesn’t get the pulse racing in quite the same way as seeing real-life explosions in the sky. Our advice is to get yourself to an organised display this weekend though, because running a good one yourself requires an awful lot of thought and equipment. Or you could try and beat the Catherine wheel word record. Go on, I dare you.

Original Image Credit: R. Gino Santa Maria / Shutterstock