Look up into the night sky this July Fourth and you'll certainly see some fireworks, but what goes into making these colorful displays?
Amy Walker is a professor with the University of Texas at Dallas. She has her Ph.D. in chemistry, so she knows a thing or two about the science behind the boom.
(Wondering what to do to celebrate? KERA’s Art&Seek has this nifty roundup, from fireworks to parades to concerts and more.)
Interview Highlights: Amy Walker
On the history of fireworks: The first recorded instance of fireworks actually is almost 2,000 years old, from China. Essentially, somebody discovered gunpowder, which is a mixture of salt peter (chemically called potassium nitrate, a little bit of sulfur and a charcoal source) and it worked that if you heated it up, it made this huge bang. They also discovered that if you put it in bamboo tubes and put it in a fire you got firecrackers, which then means that it could ward away evil spirits by making lots and lots of noise. So, this is the origin of firecrackers. It sort of moved slowly into Europe and across the Arab countries until the mid-1500s to 1700s; a lot of firework displays in Italy but they weren't what you would expect. They didn't have a lot of color with them. That happened much later. They originally started off as being for the rich and then slowly became for the masses.
On what's inside a firecracker: There are two types of fireworks: There is your aerial firework, which is your skyrocket, and there are what are called "mortars," which actually sit in tubes and are the ones you see mostly at firework displays. They're built slightly differently. A skyrocket has, at the bottom of it, some gun powder sort of around the outside of the very narrow tube. As the gunpowder goes off, it causes a lot of gas expansion and the air goes out of the bottom of the tube and lifts the rocket. If it's a mortar, the gunpowder's first charge is on the outside of the firework. The idea is it's sitting in the tube very tightly and just lifts it as that powder goes off. Then, there's a secondary time-delay fuse. Inside that is what's called a "break" and a break has stars and burning material. The stars are what makes the color, sparkles, sound and everything like that. Depending on how you lay out the stars, depending how you do the different shapes, you can actually end up with different shapes of fireworks, different timings of fireworks, different sounds, all sorts of different things they can do.
On what makes fireworks so captivating: You get the color, the sound; they just look spectacular. Who'd ever thought that from a simple firecracker you can get to all of these amazing shapes, these flowers and roman candles and different effects? You know it's been worked on for a long time — 2,000 years."
Interview responses have been lightly edited for clarity and legnth. This interview originally aired on KERA FM in July 2015.
Here's an NPR "Skunk Bear" investigation of how fireworks get their colors: