Ever wondered how fireworks actually create the shapes and colors we see in the sky?
Mike Tockstein of Pyrotechnic Innovations has a master’s degree in electrical engineering and 15 years’ experience at major firework events, including the annual Fourth of July display at the Los Angeles Memorial Coliseum. Who better to tell us about the science of fireworks in the lead up to this holiday weekend?
What exactly is a firework?
Tockstein explains that: “What you see bursting in the sky on a large professional fireworks display” is an aerial shell “that is fired out of a mortar.”
“Contrary to what many may think, the big aerial bursts you see at a typical fireworks display do not come from rockets,” but rather “from a mortar with a charge of black powder.”
“That black powder also ignites the time fuse on the bottom of the shell as it is fired. That time fuse will burn for a certain amount of time based on the size (diameter) of the shell.”
“The larger the shell, the higher it needs to go before functioning, the longer the time fuse is designed to burn. Once the time fuse burns to its end, it spits fire into the center of the aerial shell.”
That fire ignites a burst charge, which is a composition designed to produce a large volume of hot gas in a short very short amount of time. This breaks the shell open at high velocity and ignites all of its contents.
Different shells have different effects inside of them, but a standard shell contains combustible pellets, known as “stars,” composed of chemicals that burn a certain color or produce a certain look as they travel through the sky.
How are the different colors made?
“Different colors of fire are made using different types of chemicals,” Tockstein explains. “For example, Barium compounds produce green, Strontium compounds produce Red, Sodium compounds produce Yellow, and Copper compounds produce blue. Those are just the basic colors, but you can have subtle levels in between, in addition to many other fancy effects.”
How do fireworks produce different shapes in the sky?
Aerial shells are either spherical or cylindrical, Tockstein says, and “since a spherical shell breaks open in a spherical way, you can achieve patterns” such as happy faces, Saturn and its rings, or hearts simply by arranging the stars inside the shell in those patterns.
An aerial shell’s small, combustible pellets make up a firework’s “pixels,” so to speak. By inserting a piece of cardboard into the shell and then arranging the pellets in a required pattern around that, the cardboard insert forces the stars to explode outward in that pattern.
However, Tockstein explains, “patterns that are not very symmetrical are more difficult to successfully produce in the air with an exploding shell. We can produce virtually any shape, logo, word or sentence on what we call a ‘set piece’ or ‘lance work.’ These are ground mounted devices that contain a bunch of tiny ‘lances’ which are like small road flares that can be made to burn in any color.”
“The lances are arranged into the desired pattern then simultaneously ignited with ‘stickymatch’ or ‘quickmatch’ which is fuse that burns very fast.”
Is there anything else we should know about our Fourth of July fireworks?
“Although fireworks displays typically don’t use rockets, some of the shells appear to leave a trail of sparks behind them as they rise in the air before exploding at their peak. These tails were made to give the visual effect of a rocket flying into the air.”
No single person is recognized as the official designer of patterned shells, although they were likely developed in China, which is still the largest manufacturer and exporter of fireworks in the world, having first invented them in the 7th century.
Additional source: LiveScience.