How do fireworks work? The science behind why they explode, how they make shapes and get their colours

Sarah Spickernell
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It all comes down to gunpowder and metal
It all comes down to gunpowder and metal (Source: Getty)

Remember remember the fifth of November... that's today, and once again people will gather across the capital to watch fireworks displays in celebration of Bonfire Night.

But while we stand around and enjoy the event, the inquisitive among us might take a step back and wonder how on earth a mini, hand-sized rocket can turn into an explosion of light and colour way above us in the sky.

The science of fireworks all centres around little “stars” - tiny pellets within fireworks that are made of metal powders and create a coloured spark when ignited.

But to get these stars to the stage where they can explode into jets of colour, a two-stage explosion must happen, and the first part involves getting the firework off the ground.

The firework is loaded into a mortar, which is acts as a cannon, and the fuse at the bottom is lit. This ignites the first of two pouches of gunpowder, and the resulting explosion causes the firework to rocket into the sky.

Once it has travelled high enough into the air, a delay fuse is ignited inside the firework, and this runs into another gunpowder pouch called the bursting charge. This second explosion sets the “stars” on fire and creates the final spectacle.

Not all fireworks look the same – they erupt in a variety of shapes and shades, and this is made possible by the composition and alignment of the stars.

Each one turns into a jet of light, and the pattern contained within the firework translates into the pattern in the sky. So a spiral pattern of stars will turn into a spiral firework when they are set on fire.

In terms of colour, this is determined by the metal salt contained in the coating of each star. Sodium compounds turn into yellow flames, strontium into red, barium into green and copper into blue. For a multi-coloured firework, each star is coated in a different metal salt.

So when you enjoy watching a firework display tomorrow, you'll have the added pleasure of knowing exactly what's going on.

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