Rockets' red glare. Bombs bursting in air. Sure, the Chinese invented fireworks, but it took Yankee ingenuity to marry gunpowder with technology. Today's explosives are not your dad's bottle rockets, lit with the burning tip of a Lucky Strike. They're armed with electric igniters, sophisticated chemicals, and microprocessors that allow pyrotechnicians to paint the skies with shapes and color in ways impossible a few years ago.
Crack the Shell
On the surface, a firework shell is a study in minimalism - a 6-inch sphere made from cardboard or other paper-based products, sometimes painted, but typically just box brown. But inside, it's packed with high tech gizmos, an assortment of exotic chemicals, and old-fashioned black powder. Marco Polo would recognize the basics packed inside a shell: solid, lightweight pellets known as stars - made from rice hulls, soybeans, or even sawdust, and coated with combustible material. When a shell explodes, the stars ignite, creating the chest-thumping, eye-popping ooh-ah effect. The recent additions of split-second timers and computer controllers have transformed firework displays, allowing for more precision and artistry, more color and choreography. It's not cheap: A typical high-end Fourth of July show runs 30 minutes and includes some 6,000 bursts. Finales can feature more than 1,000 blasts. At up to $120 a shell, a big show can send a half-million dollars up in smoke.
Design It Onscreen
Forget flares and cord fuses. Top firework-show designers use electronic igniters to trigger detonation. The latest hardware meshes perfectly with software. New this year from Infinity Vision of Bellevue, Washington, is Visual Show Director 4D (the fourth D is time), a WYSIWYG program with OpenGL runtime that allows designers to choreograph, score, and preview their shows on a computer before the real sparks fly. It's not a fireworks show, it's a pyromusical!
Paint the Sky
In the beginning there was black powder - charcoal, potassium nitrate, and sulfur. All alone, it produces one color: pale yellow. Bor-ing. Along came the space age, and with it ammonium perchlorate, the stuff of rocket fuel. Today's stars are coated with a mixture of AP and other chlorates. Strontium burns red, barium makes green, and copper throws off blue. Magnalium (magnesium and aluminum) burns brightly, shuts down, then reignites, producing a strobe effect. Cool.
Set It Off
MagicFire of Massachusetts has developed a programmable circuit that fits inside a shell and can trigger a firework to within a millisecond of its coded instructions. A tiny capacitor charged right before takeoff powers the 0.5- by 2-inch circuit. Once launched, the chip begins its preprogrammed countdown, signaling the explosion at the instant of, say, the crash of a Souza cymbal.
Get Into Shapes
The old-style chrysanthemum burst has evolved. All sorts of shapes are now possible. To achieve a ring, for example, manufacturers sandwich a circle of stars between the two halves of the shell, which are filled with semicombustible material. A dragline (kind of like a kite tail) keeps the shell pointed in the right direction. The result: a ring writ large. Designers have begun using the technique to spell their names in the sky. Show-offs.
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