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How Fireworks Work
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When Conyers celebrates our nation's independence with a fireworks display, there will be an unseen choreographer dashing about coordinating the display. Here's what goes on behind the show.

Mortars fire around him and shells explode in bursts of light and noise. Using a flare, the technician reaches down to light the next shell in line and then quickly turns his head as the ignition wire burns to a fuse at the bottom of the mortar.

The spherical shell shoots 200 feet into the air as a second time delay fuse burns down. The powder inside ignites and the shell explodes apart.

Dozens of aluminum powder pellets, called stars, shoot out in long silver streaks forming a sphere, followed quickly by a second set of strontium carbonate stars which produce a bright red inner ring.

Just as quickly as the sky is ablaze it returns briefly to black, awaiting the crowd's next gasp.

Shine, dazzle, boom
Fireworks are big business in the U.S., yet most professional shows are still fired by hand using flares, said Pyrotecnico Sales Manager John Feigert.

Pyrotecnico is a national business with an Atlanta office that is handling 800 fireworks shows in the Northeast and Southeast, including in Covington. Only the largest celebrations will be handled by an intricate, synchronized computer program.

The world of fireworks is a true mixture of art and science. Each company has its proprietary chemical mixtures to produce unique colors, patterns and special effects.

A firework can have bursts, or breaks as they're called in the industry, with a single color, multiple colors, colors that change and sparkling effects.

"The amount of different combinations that can be made, it starts to measure in the hundreds with just those basics," Feigart said, giving the example of a sparkling silver burst with a secondary burst of red that shifts to blue.

"Take the chemical universe, that's what manufactures are working with, from zinc to titanium to chlorine."

Once a company has its color mixture and effects down, it can choose from dozens of patterns. The most standard break in the industry is the chrysanthemum or peony. The majority of flower or tree-shaped bursts, including dahlias and willow and palm trees, are the result of round ball-shaped shells.

Patterned shells are becoming more popular and form recognizable shapes, such as a bow tie, five-pointed star, happy face or peace sign.

Fireworks shows are also designed to be an auditory experience, and designers often add shells specifically designed to buzz, crackle and whistle. One such prominent shell that will be included in Covington's show is the titanium salute, which not only produces a loud "cannon shot" sound, but also provides a bright silver burst to further light up the sky. Finales combine the whole bag of tricks to create the full experience.

Designers take their entire stock, and then plot a firing pattern, mixing and matching to create an opening, a main body with mini finales thrown in and then, of course, the grand finale that leaves crowds wanting more.

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Shell sizes are measured by their diameter, and the largest shows frequently included foot long shells, but those have been reclassified as "high explosives," hiking up shipping costs and complexity, making them virtually impossible to use, Feigert said.

Even 10-inch shells are rare because some international freight companies are refusing to ship them from China, making 8-inch shells the largest you'll see in most domestic shows. Feigert said the fireworks industry doesn't consider the lack of larger shells a great loss, because they would fly so high, up to 2,250 feet, that the burst was diminished despite being larger.

Other trends in fireworks include increased computerization, as well as the advent of cakes or barrage boxes. These large groupings of shells are designed to be fire simultaneously and explode fairly low in the viewer's sightline.