Fourth of July fireworks displays have become increasingly intricate over the past few years. In a 2006 " Explainer," Slate investigated who actually synchs the crashing choruses and the flashing colors. Thecolumn is reprinted below.
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Millions of Americans will celebrate July 4 by watching a fireworks show. How do they choreograph those midair pyrotechnics?
With a pen and paper or on the computer. First, the sponsor of a fireworks show will tell the pyrotechnics company what music they want to use for their display. (Sometimes they let the company decide.) The choreographer then listens to the music several times through to get an idea of which shells to use. Felix Grucci, who does the choreography for one of America's most prominent fireworks companies, will play the piece six or seven times at high volume before he starts writing out his ideas.
Some pieces of music demand certain fireworks effects at various moments in the song. If a choreographer were putting something together for the Phil Collins song "Two Hearts," he'd probably ask for a couple of shells that burst into heart shapes.
Fireworks by Grucci uses special forms that break the display into one-minute intervals. The form specifies exactly which type of shell should be fired at each moment. To time this properly, the choreographer has to know how long it takes for each shell to open up after it's fired. For example, if he wanted two hearts to appear just when Phil Collins mentions hearts, he'd have to mark them on the form about five seconds before the words come in the song.
In general, the bigger the shell, the longer it will take to burst and the higher it will go. By inserting the size, firing time, and type of each shell into a firing script, a choreographer can lay out a series of effects that unfold at different heights in time to the music. If he's using a fireworks choreography software package, he doesn't have to look up (or memorize) all of the height and timing information for each shell. Instead, he can drag items from a digital catalog directly into an online script.
A firing script also has to specify where the shells are fired from and at what angle. A big fireworks show will make use of mortars at several locations, and each location might have guns pointing in different directions. This lets the choreographer fill up the sky with effects from left to right as well as up and down. "Angling" also helps to keep things from getting too smoky in one particular area. If too many shells go off in the same spot, a haze may start to obscure the fireworks and make bright-red bursts look a little pink.
More advanced notations for fireworks choreography have been proposed over the years. The pyrotechnics expert Takeo Shimizu used a musical score to represent his designs: Each stave corresponded to a different firing location, and each note represented a particular kind of shell fired at a particular time. In his classic work on fireworks and fireworks choreography, Shimizu argues for simple arrangements of color and form: "Mixing red and yellow stars sometimes succeeds," he says, "but red and green looks dirty." He also pointed out that some effects—like tight, round bursts—build tension in the viewer, while others—like the willow effect—tend to release it.
Explainer thanks M. Philip Butler of Fireworks by Grucci and Dorothy Drewes of American Fireworks News.