The Science Behind Fireworks
July 2nd, 2009 by Caedmon Haas
Fireworks have come a long way from the ordinary, spherical bursts of light that I enjoyed when I was a kid. Now a fireworks show can include whimsical shapes, color combinations, and even letters in the sky. How does that work, exactly?
Fireworks, whether they occur as simple bursts of light or complicated patterns, are made in the same way. All firecrackers have two components: a type of gunpowder called “black powder,” which creates the initial explosion, or “lift-charge,” and small explosives embedded in the black powder called “stars.” The stars are made from a compound very similar to the average hand-held sparkler, and come in different shapes and sizes. To make a simple firecracker that ignites on the ground, a cylinder of black powder and stars are wrapped in thick paper and a fuse is inserted in the center. When the fuse ignites, an explosion and an impressive shower of sparks results.
A row of bundled rockets are ready for launch
An aerial fireworks show is a much more complicated affair. Aerial fireworks are called “shells,” and are paper-wrapped balls of black powder and stars that can be the size of a melon or even larger. These shells are launched into the air by an initial lift-charge, much like a cannon ball is fired from a cannon. The same initial explosion lights a fuse that then causes a second explosion, blowing the shell apart in mid-air. The stars then ignite, and burn as they move out and towards the ground, resulting in the familiar ballooning light burst that we see at a fireworks show. To produce specialized effects, fireworks technicians can manipulate the shape and color of the the display depending on how the stars are positioned within the shell. For example, to produce a circular shape, stars are arranged in the shape of a circle inside the shell around a central fuse. When the firecracker is launched, the stars ignite in the same circular formation. To produce trickier shapes, like a heart or a star, the stars are pasted onto a piece of paper, which is placed in the shell with explosive charges above and below. Or shells may be placed inside each other like nesting dolls to produce a series of shapes diminishing in size. Different colors are produced by burning different chemical compounds; for example, barium flares green; copper flares blue. The composition of the stars also determines whether they will produce a bright light when ignited or the softer glittery sparkles that slowly trail down towards the earth.
These are the basics behind the science of fireworks. When you’re watching the fireworks on the 4th, try to imagine how they looked as ordinary shells before igniting. It’s truly amazing to think about the amount of precision and skill required to turn an ordinary explosion into a carefully orchestrated display of light and sound.
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Loved this ‘behind the show’ scientific explanation!
Very informative! Now I’m off to impress my friends at happy hour with what I’ve learned…