The scientific flash behind the fireworks

Beyond the basics
Well, so much for the basics. Now what about color? There are other chemicals used to produce colors, but they all only do their dazzling thanks to the first law of thermodynamics: Nature conserves energy. Energy from the fire in the basic fuel is transferred to the atoms of the colorant chemicals. That excites the electrons in those chemicals into a higher energy state. The electrons literally orbit further away from the atom’s nucleus.

Then, as they cool down, they move back to a lower state of energy. But remember, nature conserves energy. Energy is never lost, it’s just transferred somewhere else. As the electrons “calm down,” the energy they give up is converted into radiation. Light. That’s where the light of fireworks comes from. You actually see the colors in fireworks as they’re cooling down.

The signature chemicals in fireworks each emit light at a specific wavelength, producing a specific color: strontium equals red ... copper equals blue ... barium equals green ... sodium equals yellow/orange. Just as you could combine crayon colors when you were a kid, combining the colorant chemicals can give you additional colors. Strontium (red) plus copper (blue) equals purple.

The chemists produce little pellets of colorant chemicals, the size of sugar cubes, with a mixture of colorant and basic fuel blended to the right degree, and with the right-size particles so the pellet will burn at the desired rate. Then technicians can calculate how high they have to shoot their shells so they’ll be done burning before the pieces get back down to the ground.

Magic tricks with light and sound
Design artists then figure out how to get the fireworks to explode in shapes, and with sounds. The familiar whistling sound is easy. They pack some basic fuel into a cardboard tube, open on one end. As the fuel burns down inside the tube, the carbon dioxide it gives off rushes out the open end, making a whistling sound. It’s like when you whistle by blowing air out between your pursed lips.

Employees of Alonzo Fireworks set up tubes for a fireworks display in Amsterdam, N.Y. The tubes serve as launch pads for cardboard-covered shells that contain an artfully blended mix of explosives and other chemicals.

The shapes of the exploding lights depend on how the basic fuel and colorant pellets have been packed. If the explosive charge in the shell is in the middle, surrounded by a ring of pellets of sodium, when the timer fuse sets off the explosion, it ignites the sodium pellets and shoots them out into that familiar nice round yellow/orange circle. Two rows of colorant pellets around a central “bomb” gives you a double ring.

If the inside of the shell is a mix of basic fuel and colorant all interspersed, the explosion ignites the colorant pellets that then spread out and fall down in a shower, producing a glowing willow tree pattern.

To get the really tricky shapes, like stars or hearts, 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 it, and below. When those charges go off, they burn up the paper, and send the ignited colorant pellets out in the same pattern they were in on the sheet of paper, spreading wider apart as they fly.

Consumer-level fireworks, which are legal in most states, are made of the same chemicals the commercial shows use. The fireworks industry says that U.S. consumption of commercial fireworks (the big outdoor shows) plus consumer fireworks is up 400 percent since 1976, and that injuries are down 44 percent over the past four years.

But then there was the guy who stuck a lit firecracker up his nose! Honest. Or the folks who burned their house down using fireworks indoors. So if you’re going to use “home” fireworks, remember: Knowing the science behind how they work doesn’t mean they’re risk-free. Be careful while you enjoy the show.

This is an updated version of a report first published on msnbc.com in June 2000.

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