Science of the Spark - Anastasija Šlapina

by Anastasija Šļapina.

You cannot look me in the eye and say that you don’t have a single photo of fireworks on your phone. Or that you have never felt the itch to capture those illuminating moments in the sky. We usually discuss the price of the fireworks, the colours and the shapes of them - we say “that was pretty” and move on. But how did we even come about making something so beautiful, and loud, and dangerous? Have you ever wondered how fireworks work? Well, I am going to break it down for you!

It is not clear how and when fireworks were first invented. Though, it is known that firecrackers are precursors of fireworks, which were created two thousand years ago in China. Firecrackers consist of gunpowder or flash powder in a tight paper tube with a fuse. History is filled with legends about firecrackers being discovered by chance. One of these stories is about Chinese alchemists who combined honey, sulfur and saltpetre, and, when heated up, this mixture set ablaze. Another popular legend involves a Chinese cook making the same combination, which exploded when put in an enclosed space. The early gunpowder was used to scare off evil spirits, as the firecrackers created loud bangs. The gunpowder would be inserted into a bamboo stick and thrown into the fire, which made the stick explode. Later, honey was replaced by charcoal, and bamboo was replaced with small containers for the gunpowder.

If you are trying to explode something, you need a mix of fuel and an oxidizer. The fuel is a source of energy - electrons, which are small, negatively charged particles. The electrons from the fuel are transferred to the oxidizer in a combustion reaction, and because of this, energy is released. The sulfur and charcoal in the gunpowder act as fuel, while potassium nitrate acts as the oxidizer. Modern fireworks also have a binder. G-YOU MAGAZINE// FESTIVAL // NOV 2021 // 8

Usually, the backbone of a firework is an aerial shell consisting of four parts - container, stars, bursting charge and a fuse. The shell is launched from a mortar with a lifting charge (gunpowder in the container) which ignites the fuse. The fuse burns while the shell rises up to 300 meters into the sky, and at the correct point, lights the bursting charge in the shell so it explodes. With the explosion, the stars that are responsible for the colour of the fireworks start burning.

Some shells are more complicated and can explode in a sequence and have different effects in the sky. These are called multibreak shells. More common ones are round shells that produce a sphere and ring shells that make a ring in the sky. When exploding, palm shells take the shape of a palm tree by curving downwards. Since willow fireworks are long-burning, when they drop to earth they leave a path resembling willow branches.

As I mentioned before, stars generate the colour of the fireworks. The colours in the stars are achieved by the use of metal salts. In chemistry, salts mean any compounds with metal and non-metal atoms bonded together. The most typical metal salts used in fireworks to make them colourful are strontium carbonate (red), sodium nitrate (yellow), barium chloride (green) and calcium chloride (orange). Some colours are more difficult to produce. Copper salts, for instance, are unstable at higher temperatures, so it is hard to achieve blue coloured fireworks. Purple is also a hard one because it needs both copper and strontium. But how do we see the colour? Well, the heat given out in the explosion is absorbed by electrons in the metal salt atoms which causes them to be excited to higher energy levels. This excited state is not stable, so electrons release extra energy and return to their normal state. The excess energy is emitted as light. The gap between the ground and excited levels of electrons in different metals results in different wavelengths of light being emitted, which are translated into different colours.

I hope this hasn’t turned you away from enjoying the magic that fireworks can bring you. At the very least, now you know a bit of science behind fireworks and can use this knowledge when you see them next time. If you only take one message away from this, it ought to be that firework creation needs to be precise and that it is an expert craftsmanship. At the end of the day, fireworks are explosive devices, and if even a single component is off, you get an unwanted bang. So, even if you know how to light up the fuse and stand by, leave everything else to the experts.