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Scope Series 4 RTÉ Two, Thursday, 7.00pm

The science of fireworks

FireworksThe rockets’ red glare and all those bombs bursting in air - fireworks are the product of pyrotechnic chemistry that has been refined for hundreds of years, ever since the Chinese first started igniting black powder to scare away evil spirits.

Unfortunately, bad weather cancelled the 2007 Skyfest on 18 March. Not even the most advanced firework chemistry can overcome Irish weather.

The basic ingredients of all fireworks are the same: fuel and an oxidizer. The fuel’s job is to provide heat. The oxidizer is there, as its name implies, to provide oxygen so the fuel burns.

While it seems simple, there’s more to making fireworks than combining a few chemicals. The best visual effects actually come from a slower reaction. Pyrotechnic chemists strive to bedazzle and don’t want their work to fizzle too quickly. Longer burns give better shows.

To slow the burn, chemists use relatively small bits of chemicals, about the size of a grain of sand, and intentionally combine the ingredients poorly. Uneven mixing makes it harder for the fuel and oxidizer to combine and burn and produces a longer, brighter effect.

FireworksFor especially sparkly effects, larger chemical grains are used. A good example of the fuel/oxidizer/twinkle combination is the sparkler.

Sparklers are made of medium-sized grains of fuel and oxidizer, mixed with larger chunks of aluminium. When ignited, the aluminium gives off sparks – gold at 1,500 degrees Celsius, white at 3,000.

It is not just temperature that produces colour variations but also elemental additives. Generally strontium is used to make red, copper for blue, barium for green, and sodium for yellow-orange.

Interestingly enough, the colours you see in a fireworks display aren’t made as the chemicals burn but rather as they cool down and shed their excited electrons in the form of light.

Technicians calculate how high to shoot the firework shells so they finish burning before any pieces hit the ground – or spectators.

Design artists determine how to get the fireworks to explode in shapes and sounds. The characteristic whistling noise comes from fuel being packed into a cardboard tube open at one end. As the fuel burns down carbon dioxide whistles out the open end.

Shapes depend on how the fuel and colorant are packed. If the inside of the shell is a mix of fuel and colorant the pellets spread out and shower down like a giant glowing willow tree.

If the explosive charge is in the middle of the shell surrounded by a ring of colorant, when the fuse sets off it ignites the colorant and shoots it and out in a circle. Adding another row of a different colour produces a double ring.

For more elaborate shapes the colorant pellets are pasted on a piece of paper in the desired pattern. That paper is put in the middle of the shell with explosive charges above and below. When the charges go off, they burn the paper and propel the pellets according to pattern.

Dublin’s extravagant St. Patrick’s Day Skyfest is Europe’s largest annual fireworks show and was created by Kimbolton Fireworks, the only manufacturer of large displays in the UK.

 

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