The Science Behind Firecrackers and Sparklers

Fireworks in the sky behind buildings

Hiroyuki Matsumoto / Photographer's Choice / Getty Images

Fireworks have been a traditional part of New Year's celebrations since they were invented by the Chinese almost a thousand years ago. Today fireworks displays are seen on most holidays. Have you ever wondered how they work? There are different types of fireworks. Firecrackers, sparklers, and aerial shells are all examples of fireworks. Although they share some common characteristics, each type works a little differently.

Key Takeaways: How Fireworks Work

  • Not all types of fireworks explode, but they all contain a fuel and a binder.
  • The binder often acts as an oxidizer that helps a firework burn brighter.
  • Many fireworks also contain colorants.
  • Fireworks that explode in the air contain a propellent. Basically, this is a fuel within a container that forces combustion to release energy in one direction so the firework goes up.

How Firecrackers Work

Firecrackers are the original fireworks. In their simplest form, firecrackers consist of gunpowder wrapped in paper, with a fuse. Gunpowder consists of 75% potassium nitrate (KNO 3), 15% charcoal (carbon) or sugar, and 10% sulfur. The materials will react with each other when enough heat is applied. Lighting the fuse supplies the heat to light a firecracker. The charcoal or sugar is the fuel. Potassium nitrate is the oxidizer, and sulfur moderates the reaction. Carbon (from the charcoal or sugar) plus oxygen (from the air and the potassium nitrate) forms carbon dioxide and energy. Potassium nitrate, sulfur, and carbon react to form nitrogen and carbon dioxide gases and potassium sulfide. The pressure from the expanding nitrogen and carbon dioxide explode the paper wrapper of a firecracker. The loud bang is the pop of the wrapper being blown apart.

How Sparklers Work

A sparkler consists of a chemical mixture that is molded onto a rigid stick or wire. These chemicals often are mixed with water to form a slurry that can be coated on a wire (by dipping) or poured into a tube. Once the mixture dries, you have a sparkler. Aluminum, iron, steel, zinc or magnesium dust or flakes create the bright, shimmering sparks. An example of a simple sparkler recipe consists of potassium perchlorate and dextrin, mixed with water to coat a stick, then dipped in aluminum flakes. The metal flakes heat up until they are incandescent and shine brightly or, at a high enough temperature, actually burn. A variety of chemicals can be added to create colors. The fuel and oxidizer are proportioned, along with the other chemicals, so that the sparkler burns slowly rather than exploding like a firecracker. Once one end of the sparkler is ignited, it burns progressively to the other end. In theory, the end of the stick or wire is suitable to support it while burning.

How Rockets and Aerial Shells Work

When most people think of "fireworks" an aerial shell comes to mind. These are the fireworks that are shot into the sky to explode.

Some modern fireworks are launched using compressed air as a propellant and exploded using an electronic timer, but most aerial shells launch and explode using gunpowder. Gunpowder-based aerial shells essentially function like two-stage rockets. The first stage of an aerial shell is a tube containing gunpowder, that is lit with a fuse much ​like a large firecracker. The difference is that the gunpowder is used to propel the firework into the air rather than explode the tube. There is a hole at the bottom of the firework so the expanding nitrogen and carbon dioxide gases launch the firework into the sky. The second stage of the aerial shell is a package of gunpowder, more oxidizer, and colorants. The packing of the components determines the shape of the firework.

How Fireworks Get Their Colors

Fireworks get their colors from a combination of incandescence and luminescence.

Incandescence is red, orange, yellow, white, and blue light produced by heating metal until it glows. This is what you see when you put a poker into a fire or heat a stove burner element.

Most colors come from luminescence. Basically, metal salts in the firework emit light when they are heated. For example, strontium salts make red fireworks, while copper and barium salts produce blue and green colors. The emitted light is the basis for the flame test in analytical chemistry, which helps identify elements in an unknown sample.

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Helmenstine, Anne Marie, Ph.D. "The Science Behind Firecrackers and Sparklers." ThoughtCo, Jul. 1, 2021, thoughtco.com/how-fireworks-work-pyrotechnics-science-607860. Helmenstine, Anne Marie, Ph.D. (2021, July 1). The Science Behind Firecrackers and Sparklers. Retrieved from https://www.thoughtco.com/how-fireworks-work-pyrotechnics-science-607860 Helmenstine, Anne Marie, Ph.D. "The Science Behind Firecrackers and Sparklers." ThoughtCo. https://www.thoughtco.com/how-fireworks-work-pyrotechnics-science-607860 (accessed October 17, 2021).