It's time to light up the nighttime skies with plenty of red, white and blue -- and yellow, orange and green, too.
Producing the colorful bursts that keep eyes glued to the skies on the Fourth of July has everything to do with chemical engineering, according to Stefan Bossmann, professor of chemistry at Kansas State University.
"The art of fireworks is the packaging," Bossmann said. "What the firework does depends on what's inside."
What's inside includes a fuse and fuel to make the firework explode. This fuel is typically a powder of charcoal, sulfur and potassium nitrate -- similar to gunpowder, Bossmann said. Also inside are one or more capsules or packets containing metals ground into tiny particles. When the firework explodes, the metal particles start oxidizing, which creates heat.
"The heat is needed to excite the metal particles so they can emit light," Bossmann said.
We see the lights the metals emit as colors.
"Different metals produce different colors," Bossmann said. "For example, think of liquid steel. When it gets hot it turns yellow."
Metals used in fireworks today include aluminum, titanium, beryllium, barium, copper, potassium and more. Here's a look at the metals used to produce a specific color:
* Red --Strontium and lithium
* Orange --Calcium
* Yellow -- Sodium
* Green -- Barium
* Blue -- Copper
* Violet -- Potassium and rubidium
* Gold -- Charcoal, iron or lampblack
* White -- Titanium, aluminum, beryllium or magnesium powders
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