On this 4th of July, as America celebrates its independence, you might be thinking that fireworks couldn’t get any better – or didn’t need to. But chemist and pyrotechnic specialist John Conkling tells us that the choreography of these shows is nearing perfection, thanks to advances in firing technology. The next big thing may be mastering patterns. But the question remains: Will they ever get a handle on…blue?
Credit: Flickr / bayasaa
“If you’re playing the Star-Spangled Banner, when you get to the part ‘and the rockets’ red glare’, that’s the moment you want the sky to explode in red!” This is the advice for your 4th of July fireworks, offered by John Conkling, Professor of Chemistry, Emeritus, at Washington College (Maryland) and renowned pyrotechnics expert. The next line of America’s national anthem—“the bombs bursting in air”—calls for a perfectly timed bang-bang-bang from another set of exploding shells. This sort of precision choreography, says Professor Conkling, is where the fireworks industry has made its biggest advances in the last few years, in the firing technology.
Whether they end as a colorful starburst or a white, snaky sizzle, all fireworks start out as round shells—usually from three inches across for a small burst diameter, to 12 inches for the big ones. They are loaded with propellant at the bottom, which, when ignited, explodes in the launching tube, rocketing the shell up into the air. A delay fuse allows it to reach a specific height before the spectacular-color-producing pellets inside explode. “In the olden days, when I was first involved,” John Conkling remembers, “the operator hand-lit the fuses with a flame. It was a slow operation and impossible to choreograph. Now, the technology is getting better and better. All the mid-sized shows and up are fired electronically.” The shells are still loaded in a launching tube, but wires connect them to a computer, which sends a signal to an “electric match”. Ignition can be timed to the millisecond, allowing fireworks specialists to program their show to a musical score.
Big Independence Day shows can take months to prepare, Conkling says. The designers will start working with a client in February, take the requested piece of music and begin creating their work of art. They’ll look at the audio signature, identify the peaks and valleys, and make sure the perfect effect in the sky will match the most moving moments in the music. “Disney World has this show they do every night for a year, so they have the chance to perfect it. But even one-time shows, they’re awfully close to perfection,” Conkling says.
Master orientation to learn to spell
The other major area of progress in the fireworks field is in the complexity of patterns that can be produced. Inside each shell are marble-sized pellets of a chemical composition designed to emit a certain color when heated to the temperatures reached at the moment of explosion (from 1,000 to 2,000°C). The way these pellets, called stars, are arranged in the shell determines the shape of their burst: a perfect circle, a heart.
Because orientation is crucial for these fireworks to have their effect, shells of this sort are fired in flights, or sets of five or six, maximizing the chances that the audience will get to enjoy at least one that is facing just the right way. “That’s the problem with spelling,” Professor Conkling explains. “We’re not there yet.” To spell out a word, C-A-T, for example, with three fireworks, “you need to maintain perfect orientation.”
Better colors through chemistry, but no brilliant blues
Finding a safe way to weight the shells, forcing them into the right orientation, is a line of fireworks R&D still being pursued. Another, ongoing theme is the development of new colors. This is where the chemists, the “wizards” of pyrotechnics, come into it. “We totally rely on Mother Nature,” John Conkling says, referring to the property of certain chemical elements to emit a particular color of light, visible to the human eye, at high temperatures. When heated, the atom’s electrons become excited, taking on extra energy. As soon as they cool slightly, though, they release this extra energy in the form of light. The color depends on the chemical: “Barium will give you a fairly respectable green, sodium gives you an intense yellow-orange flame. If you have metals in the composition, like magnesium or aluminum, they emit a large spectrum of light, so it’s a dazzling white” says the chemist.
Clients seeking a particular color for a specific effect might request that a fireworks producer create, for instance, a pumpkin orange. But if it’s a shade of blue they’re looking for, they may be disappointed. “Blue is difficult,” Conkling acknowledges. The copper that produces it is “a very, very fragile atom with respect to light emission. There’s a certain minimum critical temperature, but if it gets too high, it washes out the color.” With other elements, it is precisely this high temperature that allows for brighter hues.
Even without the copper conundrum, designing new colors for fireworks takes a great deal of trial and error in the lab – weeks or months – to get the recipe just right. The three principal ingredients are the color-generating chemical, the fuel, and an oxygen-carrying compound to let it burn. The ratio of these three determines how fast it burns and how hot it gets, essential for controlling both the timing and the color.
This year, when you take in a fireworks show, remember to appreciate all the hard working researchers behind it, busily inventing new ways to make our biggest celebrations ever more spectacular. And notice—do you see any vibrant blue in the night sky? Maybe next year…
Find out more:
"Beyond the Boom", an infographic on the fireworks industry