Burning metals on a Bunsen burner to see what colour they glow has long been the highlight of secondary school science classes. Years later, we all relish that nostalgia (perhaps unknowingly) when watching fireworks create colourful, pretty patterns in the sky.
But have you ever wondered, as you’ve sat crunching down on your bonfire toffee or trying to write your name with a sparkler, what kind of wizardry makes this all possible? Well, fireworks are the love child of science and engineering, requiring a perfect combination of chemistry (to get the pretty colours) and engineering (to get them high enough in the sky and at the right time so they’re not exploding in your face).
All fireworks, no matter how bright or loud, are created from 5 core components: a fuel, an oxidiser, a chlorine donor, a binder and a colour producer.
Though Guy Fawkes’ plot to blow up the houses of Parliament in 1605 was an enormous fail, gunpowder is still used today as one of the main components in fireworks. Gunpowder (composed of sulfur, potassium nitrate and charcoal) acts as a fuel, which triggers the firework to burn. Very fine gunpowder is used along the fuse, allowing it to burn at a controlled rate so that whoever is lighting the firework has enough time to run as fast as they can in the opposite direction. The fuse then lights larger granules of gunpowder that line the bottom of the firework, exploding and propelling the firework into the sky. The large pellets of gunpowder that are packed into the body of the firework then eventually explode and force the firework to burst apart.
In order for the fuel to combust, oxygen is required. Chlorates, nitrates and perchlorates are used to supply the fuel with oxygen and cause it to combust. This is the part where the firework goes bang and your dog starts barking incessantly. Chlorates produce high amounts of oxygen as they become completely reduced and so cause a spectacular reaction. To make the fireworks brighter than the moon, moon, moon (yes, we often pop on a Katy Perry banger – big fans), chlorine donors are used to intensify the colours, with chlorate and perchlorate acting as both a chlorine donor and an oxidiser (we love a good multitasking metal).
The metaphorical glue (known as a binder) that holds all these components together is usually a starch called dextrin, which is dampened with water to generate a paste that keeps everything held tightly.
To jog your memory back to that secondary school science lesson, different metals emit different colours when burned. When you heat a metal ion (like those found in fireworks), electrons are promoted from their normal state, into a higher and more excited state. As these electrons fall back down to their normal energy levels, the excess energy is released in the form of a photon (light); these falls involve a specific amount of energy, which correspond to a particular wavelength, and so is emitted as a particular colour of light. For example, strontium burns red, while calcium glows orange. If you wanted a green firework, you’d use barium, but for yellow, you’d choose sodium. The metal ion determines the colour of the firework, and so, they’re called colour producers.
The explosion of a firework is a beautifully curated sequence of events, leading to a spectacular, colourful display. It starts with a fuse being lit and ends with the packets of metal salts blowing apart, forming glowing colours through a culmination of chemical principles – definitely worthy of a few ‘ooos’ and ‘aaahs’.
The fact that you can buy these bad boys, packed full of science and technology, for just a tenner at ALDI is pretty incredible. Now, when you watch your Catherine wheels spin round on your fencepost, hopefully you’ll see it with a new enthusiasm for the science behind the magic.
- The Chemistry of Fireworks. Available at: https://www.compoundchem.com/2013/12/30/the-chemistry-of-fireworks/. Accessed November 2020.
- The Chemistry behind a Firework Explosion. Available at: https://www.theverge.com/2015/7/3/8886697/the-chemistry-behind-a-firework-explosion. Accessed November 2020.
- The Composition of Fireworks. Available at: https://www.ch.ic.ac.uk/local/projects/gondhia/composition.html. Accessed November 2020.
- The Chemistry of Firework Colours. Available at: https://www.thoughtco.com/chemistry-of-firework-colors-607341. Accessed November 2020.