How are the colours and shapes of fireworks created?
In China, fireworks were traditionally used to scare off evil spirits, but the science behind their beautiful colours is anything but supernatural.
Asked by: Matt Stringer, St Albans
Despite being invented in China almost 1,000 years ago, fireworks involve some pretty sophisticated science. The spectacular colours are the result of metal compounds combining with oxidisers that supply oxygen. This produces heat, which kicks electrons in the chemicals into higher energy levels. They rapidly return to their normal ‘ground state’, and shed the energy as light. Relatively cool-burning strontium carbonate gives red, sodium nitrate produces yellow, and barium chloride gives green. The hardest colour to produce is an intense blue, which needs the firework to reach a high temperature, but not so high that it simply burns up. Manufacturers often use copper chloride to hit the right temperature range and achieve a bright, rich blue.
The spectacular shapes are produced by embedding the packets containing the colour-making chemicals – known as ‘stars’ – in gunpowder, together with a burst charge. Once the firework reaches the right altitude, the burst charge explodes, detonating the gunpowder, and blasting the stars out into the pre-arranged pattern.
Robert is a science writer and visiting professor of science at Aston University.