Firework Science: The Chemical Elements Behind Colorful Explosions In The Sky [PHOTOS]

on July 02 2013 5:27 PM

Firework displays will dazzle Americans from coast to coast this Thursday. But while you might have Thomas Jefferson to thank for the Declaration of Independence -- and by extension, the Fourth of July -- it’s chemistry that powers those colorful explosions in the sky.  

Fireworks display different colors due to the various kinds of materials packed inside them. When certain metals are heated to a certain temperature, electrons momentarily jump to a different energy level. When the electron settles back down to its original energy level, that cooling process emits a photon. Depending on the material, the photon will have a different wavelength and, hence, a different color.

For instance, while sodium appears gunmetal gray in person:

sodiumbricks Sodium, by itself, doesn't look much like table salt (which is a compound of sodium and chlorine).  Wikimedia Commons/Dnn87

It creates bright yellow light when it burns:

yellowfirework This sunburst-like firework gets its yellow hue from sodium.  Flickr via Creative Commons/pictureclara

You can see this effect in sodium lamps as well:

sodiumlight Sodium lights burn bright.  Flickr via Creative Commons/PinkMoose

Barium, which when compounded with sulfur and oxygen is used in X-ray imaging of the digestive system, is also used in fireworks to produce a green color. Yellowish green colors come from the compound barium chloride; barium nitrate gives a brighter green.

bargreen Barium can either make your colon show up on an X-ray, or make your fireworks verdant.  L: Wikimedia/Matthias Zepper; R: Wikimedia/Joe Anderson

The element strontium was primarily used in the production of glass for color TVs and computer monitors, thanks to its X-ray-shielding properties. It can also give fireworks a deep red color.

strontred Strontium bathes explosions in a crimson glow.  L: Wikimedia/alchemist-hp; R: Flickr/junctions

Blue was a tricky color for pyrotechnicians for some time, since the traditional material used, copper chloride, didn’t survive well enough at high heat to produce a vibrant display. But in recent decades, makers of fireworks have found success with a magnesium-aluminum alloy called magnalium.

magblue Magnalium may be a shiny silver, but it burns bright blue.  L:; R: Flickr/Chris Erwin

Other substances besides the color-generating material are also used in fireworks. To slow or speed the burn rate, pyrotechnicians can add sulfur or sugars (to make it burn faster) or salt (to slow it down).

sulfur Sulfur might smell like rotten eggs, but it is often a necessary firework ingredient  Wikimedia Commons/Ben Mills

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