A trio of components make for the best Fourth of July fireworks displays. Safety and a clear night sky should be two of them. But that's a different kind of list. The chemistry behind the biggest and brightest bangs involves another threesome: Oxidizers, fuel, and colors. That's the gospel according to John A. Conkling, a chemist at Washington College in Maryland who wrote the book on fiery displays. (He really did, and it is called The Chemistry of Pyrotechnics: Basic Principles and Theory, now in its second edition.) This week Conkling described how these three ingredients combine in a holiday blast for the American Chemical Society's Reactions blog:
Oxidizers are chemicals that carry oxygen, needed to power a high-heat reaction. Potassium nitrate, in a black powder, is a common one for fireworks. They combine with fuel, the second component, to release that heat. Sulfur can serve as a fireworks fuel, as can charcoal, Conkling says. But the real fun comes with the third ingredient, chemicals that produce colors. "Different chemical elements, heated to high temperatures, get rid of that energy by emitting very different wavelengths of light," he says. If you want a very nice blue flame color, copper oxide is a good choice, Conkling says. Strontium chloride will give you a good red. And calcium nitrate "makes a nice yellow-orange."
Safety is on his list too, says Conkling, who wears protective glasses when handling these compounds. Pretty things that blow up command respect.