There's no tradition quite like a Fourth of July fireworks display. Lawnchairs and blankets line the grassy viewing area as spectators wait for spellbinding colors, thrilling explosions and intriguing shapes to paint the sky. The event may be magical—especially for the kids—but of course, its all the product of meticulous chemistry and clever ballistics.

Behind the curtains—out on a river barge floating a distance from the onlookers' vantage point—are brown cylindrical and spherical canisters of varying sizes, placed in mortar tubes and wired to a central control. An engineer pushes a button that routes an electrical impulse through 40 feet of wiring to the first canister. The impulse lights a fuse at the canister's base, which burns through to a black powder that catapults the shell into the sky. At the same moment, a time-delay fuse is triggered, giving the shell time to soar before bursting. After about 5 seconds the shell peaks, the fuse kindles a bursting charge, and poof!—the casing ruptures, and magnificent tendrils of red, white and blue stream into the sky.

If one thing is off—too much black powder or a misplaced trigger—everything can fail

Every step of this process is a complex, carefully crafted process. If one thing is off—too much black powder, misaligned stars or a misplaced trigger—everything can fail. Here's a look at how professionals pull it off every year while one-upping last year's pyrotechnic display.

The Shell

Fireworks start off as handcrafted shells that are fairly unassuming, encased in treated cardboard and heavy paper. But inside these shells are the blueprints that control how a firework will take off, detonate and appear across the canvas of the night sky. The shell innards include fuel, an oxygen producer, a binding resin and color-producing agents all carefully mixed into a recipe that renowned pyrotechnical companies like Zambelli Fireworks Internationale in New Castle, Pa., and Pyro Spectaculars in Rialto, Calif., keep locked up. The most familiar characteristics of a firework are its radiant tendrils and plumes that stream out as the shell breaks open. Each of these colorful protrusions has a matching pyrotechnic pellet or star, an identical seed within the shell.

The particular arrangement of the stars within the shell determines how the firework will unfold in space. A smiley face or a star-shaped arrangement, for instance, will burst into fireworks with exactly those shapes. Stars themselves come in many shapes and sizes, from round, dough-like balls to pressed pieces that resemble everyday batteries. Still other stars can be meticulously hand-packed into small tubes and inserted into the shell to generate a rocket-powder effect, sending swarms of color along squiggly trajectories.

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The round stars can be as small as a pea or as large as a clementine. Larger pellets have more material to burn, causing the plume that spews from it to spread farther into space and to last longer.

The pressed pellets are commonly called comet stars because they produce a broad brush-stroke effect as opposed to the skinnier filaments that arise from round stars. Because comet stars have more mass to them, they also burn for a longer duration of time, leaving frayed edges and sweeping plumes that are peculiar to palm-tree fireworks.

The Ingredients

Firework anatomy doesn't end with the bursting charge and the pyrotechnic stars. There are about 30 other ingredients vital to the recipe's success. To keep all of the pieces in place and prevent crumbling, pyrotechnicians add a binding agent such as dextrin to them.

A black powder made up of 70 percent potassium nitrate, 15 percent charcoal and 10 percent sulfur is used to propel the shell into the air from the mortar-launching tubes on the ground. As the mixture reacts together, the charcoal fuel binds to some of the oxygen molecules that leave the potassium nitrate. The charcoal-oxygen compound that results needs only a small amount of energy to combust. There's also a time-delay fuse tucked into the shell casing's lid. This fuse determines the length of time a shell will soar before exploding. The longer the time-delay fuse, the more time there is before the shell explodes.

There are about 30 other ingredients vital to the recipe's success

Once ignited, the lift charge thrusts the shell into the air and simultaneously sets off the time-delay fuse, which burns to the inside of the shell and lights the bursting-charge gunpowder at its core. The shell explodes and the stars are jettisoned. All this happens in a matter of about 5 seconds for the higher, 1200-foot explosions.

Zambelli says there's an even better recipe for this black lift powder, one that incorporates potassium chlorate instead of potassium nitrate. This substitute speeds up the rate of oxygenation, resulting in much more brilliant color displays. "[This] took the degree of heat from 1700 degrees Celsius to 2000 C, and you get better firework burn," he says.

Special Effects

Modern technology has made it possible to utilize more of the boundless night canvas for multi-shot displays and captivating grand finales. Over 46,000 fireworks are set off within 30 minutes for the displays that Zambelli's company produces in Louisville, Miss. It takes 2 hours of planning just to execute a single minute of firework choreography, he says.

Glitter: Some shells can be designed to break in the air at heights of 1200 feet, at lower points of about 100 feet, and still others beneath them gush from the ground in glittering lances, feathery fountains, fan shapes and flickering Roman candles. Roman candles erupt from tubes about 3 feet tall and 2 inches in diameter. A bunch of mini-cannonball pellets can be stacked on top of each other within the tubes, and when lit, the Roman candles flicker for 30 seconds or more. Little strobes are tucked inside the tubes as well as in any firework shell to give off a glittering golden feather effect at the edges.

Claws: By boring holes in special cylindrical components and hand-loading them into the shell casing, you can change the animation at the tip of the firework's tendrils, producing a firework with talons.

Animation: Fireworks that start as one color and blossom into others with forked or undulating animation at the tips are made with alternating round golden pellets at the shell's core with crimson comet pellets at the shell's perimeter to make the firework filaments start off skinny and then peel out more widely at the tips, all while revealing a new color.

Tails: Before the shell is sealed, one star is designated as the tail, which is more glorious than the name implies. This single tail star simply has a shorter time-delay fuse than the others, causing the star to ignite at the same time as the lift charge at takeoff. The tail is illuminated as the rest of the shell remains intact until the zenith is reached and the bursting charge detonates the firework.

Endless Finales: Multibreak shells create the seemingly endless firework explosions of the grand finales. A multibreak shell is either a single large cartridge containing several smaller shells or multiple casing layers. By varying the lengths of the time-delay fuses in each compartment of the multibreak shell, sequential bursts can arise from the same shell. The initial explosion of the outermost shell causes the others to disperse across the sky before breaking open like a bouquet.

Colors

Every pyrotechnic company has a unique approach to pinpointing a desired color, from the intense oranges and reds at one end of the spectrum to the rich violets and blues at the other. But the secret to vibrant colors lies in the stars' chemical makeup. Each color has a distinct recipe, which specifies the precise chemical concentrations of the compounds that should be mixed, as well as sophisticated techniques for grinding, mixing and sculpting these compounds into stars.

A calcium salt formula, like calcium chloride, molded into small, round stars will give rise to an orange peony firework. These small stars are loaded into the shell around its centerpiece, the bursting charge, which is made of gunpowder.

When the shell has soared to its selected height, the bursting charge ignites and burns the stars around it, eventually causing the entire shell to explode. The power of the burst charge, the strength of the shell walls and the size of the stars all determine the shape and width of the display.

As the peony stars heat up, the electrons of each calcium atom whir around, absorbing energy from the heat, and become excited, jumping from their lowest-energy state, the ground state, to the higher-energy state. The surplus energy from this excitement is emitted as light, spewing forth as rich red-orange rays.

The amount of light energy emitted in such a reaction depends on the elements that are interacting with one another, which in turn determine the firework's color. Lower energies have a corresponding longer wavelength of light at the red end of the spectrum, while higher energies correspond to shorter wavelengths—the violets and blues.

Calcium gives off less energy than other elements and corresponds to a longer wavelength of light, in this case a brilliant orange. Mixtures of strontium carbonate and copper oxide produce violet hues, one of the most difficult colors to pull off in a display, says George Zambelli Jr., the chairman of Zambelli Fireworks Internationale. Emerald and olive colors arise from various barium compounds, and crimsons and corals from strontium and lithium carbonates.

According to Zambelli, a shell can contain up to eight different colored stars, erupting into a rainbow comet of intermingling magentas, oranges, greens, yellows and blues.

The Recipe

Here is a firework recipe for a blue violet eruption, Blue violet (422 nm), by Zambelli.

Composition by weight:

Potassium perchlorate, KClO4: 70%

Polyvinyl chloride: 10%

Red gum: 5%

Copper oxide, CuO: 6%

Strontium carbonate, SrCO3: 9%

Much of this information was derived from Zambelli: The First Family of Fireworks by Gianni DeVincent Hayes.

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