Whether you’re celebrating Independence Day or Mexico’s advancement in the World Cup (until Brazil put an end to that), fireworks are popular in the months of June and July. Fireworks, from their brilliant colors to their impressive noises, are all displays of chemistry at work. Let's look at what gives fireworks their colors, their sounds, and even their shapes.
The history of fireworks is usually traced back to medieval China, although legends vary as to exactly how they were invented. A Chinese monk from the seventh-century B.C.E. named Li Tian is often credited with creating the first firework. According to lore, he stuffed gunpowder into a bamboo shoot and threw it into a fire, and boom! He is celebrated in parts of China with fireworks displays every April. Other legends claim the first fireworks came from a cook working in the fields who attempted to cook food by mixing sulfur, charcoal, and saltpeter (also known as potassium nitrate). In the United States, using fireworks to celebrate independence and as a morale booster date back as far as the Revolutionary War.
How Do Aerial Fireworks Work?
The mix of material that create the currently popular aerial fireworks, or the fireworks that explode in colorful lights and loud noises high above us in the sky, are encased within an outer shell, sometimes called a mortar. When the firework is first lit, the so-called lift charge ignites a type of gun powder at the base of the firework which sends the mortar shell and its contents shooting up into the air.
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The star of the firework show are the small, explosive pellets of 1-1.5 inches in diameter called, well, "stars." They are little packets of fuel, an oxidizing agent, and a binding agent, mixed with metallic salts or oxides. Once safely high in the air, delayed bursting charges ignite the stars while the explosion also creates a high pressure gas that sends the stars bursting out of the mortar shell.
How Do Fireworks Get Their Colors?
The multitude of firework colors are achieved by varying the different metallic salts or oxides added to the mix. The fuel and oxidizing agent together make an intense amount of heat very quickly which activates or heats up these metal colorants. The metallic atoms become what we call excited or, in other words, their electrons gain energy and are bumped up to a higher energy state. Once the fuse is exhausted and the temperature cools again, those electrons return back down to their normal, lower energy state. The extra energy they once had gets emitted in the form of light.
The energy required to bump an electron up to the next energy level (and thus the energy that gets emitted once the electron moves back down to its normal state) varies depending on the kind of atom or metal. That quantized amount of energy in turn determines the wavelength or color of light that gets emitted.
- Barium will give you a green firework display.
- Sodium produces a gold display.
- Orange fireworks are the result of calcium salts.
- Red fireworks come from lithium or strontium salts.
- Magnesium will give you a white display.
- Copper chloride shines blue.
Some fireworks contain layers of the different metals so that the aerial display shines with different colors at different stages.
How Do Fireworks Get Their Sound?
Fireworks aren’t just visual displays, of course. It’s not the lights that send your dog running to hide behind the couch but the loud cracking sounds. Each pop or boom is actually the sound of chemistry in action. The sharp, loud pops that are most common in aerial shows are the sound of the burning or the bursting charges together with their color-producing metal powder mixtures. Fireworks that use gunpowder create a louder, deeper boom as the powder ignites.
How tightly the stars are packed into the firework shell also impacts the noise they produce. For example, to create that whistling sound that some fireworks make as they rocket up into the air, stars are packed into a small narrow tube so that—as they light—they are forced down the tube much like with a mechanical whistle. Some manufacturers are also looking to create more loosely packed fireworks that will result in quieter displays that don’t bother the neighbors.
However you plan to celebrate with fireworks this summer, always read the cautionary labels on your fireworks!
The Shape of Fireworks
The arrangement of those stars inside the firework shell casing can also determine the shape of the firework in the sky. If the pyrotechnic technician assembling the firework wants lights in the form of a heart in the sky, the stars are arranged in the shape of a heart inside the mortar shell. They can pack materials that do not burn in between the stars to help them maintain their shape.
How Do Sparklers Work?
Sparklers are miniature, more controlled handheld versions of their aerial counterparts. A sparkler’s metal wire is dipped in a mixture of metallic fuel, an oxidizer, and a binding material that dries into a kind of putty. The fuel, commonly aluminum or magnesium, creates sparks when lit, while the oxidizer, usually potassium nitrate, provides oxygen to keep the spark going. Both the fuel and the oxidizer are proportioned out along the wire so the sparkler burns slowly and gradually, rather than all at once. The binding material, a flammable starch or sugar, is only there to hold the mixture together and to burn away once lit.
However you plan to celebrate with fireworks this summer, always read the cautionary labels on your fireworks so that you understand their proper use. Light one at a time in a clear open area away from buildings and keep a bucket of water nearby just in case. Also, don’t make your own!
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.
Image courtesy of shutterstock
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