Fireworks may seem magical, but the science behind them is easy to understand. Learn how fireworks and firecrackers work.

Introduction to How Fireworks Work

If you have ever been to an aerial fireworks show at an amusement park, baseba­ll game, Fourth of July celebration or on New Year's Eve, then you know that fireworks have a special and beautiful magic all their own -- a good show is absolutely amazing.

­Have you ever wondered how this magic works? What is launched into the sky to make these beautiful displays? In this article, you will learn all about firecrackers, sparklers and aerial fireworks.

Just about everyone in the United States has some personal experience with fireworks, either from Fourth of July or New Years Eve celebrations. For example, you have probably seen both sparklers and firecrackers. It turns out that if you understand these two pyrotechnic devices, then you are well on your way to understanding aerial fireworks. The sparkler demonstrates how to get bright, sparkling light from a firework, and the firecracker shows how to create an explosion.

Firecrackers have been around for hundreds of years. They consist of either black powder (also known as gunpowder) or flash powder in a tight paper tube with a fuse to light the powder. Black powder, discussed briefly in How Rocket Engines Work, contains charcoal, sulfur and potassium nitrate. A composition used in a firecracker might have aluminum instead of or in addition to charcoal in order to brighten the explosion.

Sparklers are very different from firecrackers. A sparkler burns over a long period of time (up to a minute) and produces extremely bright and showery light. Sparklers are often referred to as "snowball sparklers" because of the ball of sparks that surrounds the burning portion of the sparkler. If you look at Patent #3,862,865: Sparkler composition, you can see that a sparkler consists of several different compounds:

  • A fuel
  • An oxidizer
  • Iron or steel powder
  • A binder

See this Question of the Day for a discussion of oxidizers -- potassium nitrate is a very common one. The fuel is charcoal and sulfur, as in black powder. The binder can be sugar or starch. Mixed with water, these chemicals form a slurry that can be coated on a wire (by dipping) or poured into a tube. Once it dries, you have a sparkler. When you light it, the sparkler burns from one end to the other (like a cigarette). The fuel and oxidizer are proportioned, along with the other chemicals, so that the sparkler burns slowly rather than exploding like a firecracker.

It is very common for fireworks to contain aluminum, iron, steel, zinc or magnesium dust in order to create bright, shimmering sparks. 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.

In the ­next section, we'll look at aerial fireworks, such as those you might see in a fireworks display.­

Aerial fireworks are the large, colorful fireworks you might see in a Fourth of July show.

Aerial Fireworks

An aerial firework is normally formed as a shell that consists of four parts:

  • Container - Usually pasted paper and string formed into a cylinder
  • Stars - Spheres, cubes or cylinders of a sparkler-like composition
  • Bursting charge - Firecracker-like charge at the center of the shell
  • Fuse - Provides a time delay so the shell explodes at the right altitude

Located just below the shell is a small cylinder that contains the lifting charge.

The shell is launched from a mortar. The mortar might be a short, steel pipe with a lifting charge of black powder that explodes in the pipe to launch the shell. When the lifting charge fires to launch the shell, it lights the shell's fuse. The shell's fuse burns while the shell rises to its correct altitude, and then ignites the bursting charge so it explodes.

A simple shell used in an aerial fireworks display. The blue balls are the stars, and the gray is black powder. The powder is packed into the center tube, which is the bursting charge. It is also sprinkled between the stars to help ignite them.

Simple shells consist of a paper tube filled with stars and black powder. Stars come in all shapes and sizes, but you can imagine a simple star as something like sparkler compound formed into a ball the size of a pea or a dime. The stars are poured into the tube and then surrounded by black powder. When the fuse burns into the shell, it ignites the bursting charge, causing the shell to explode. The explosion ignites the outside of the stars, which begin to burn with bright showers of sparks. Since the explosion throws the stars in all directions, you get the huge sphere of sparkling light that is so familiar at fireworks displays.

Multibreak Shells

More complicated shells burst in two or three phases. Shells like this are called multibreak shells. They may contain stars of different colors and compositions to create softer or brighter light, more or less sparks, etc. Some shells contain explosives designed to crackle in the sky, or whistles that explode outward with the stars.

Multibreak shells may consist of a shell filled with other shells, or they may have multiple sections without using additional shells. The sections of a multibreak shell are ignited by different fuses. The bursting of one section ignites the next. The shells must be assembled in such a way that each section explodes in sequence to produce a distinct separate effect. The explosives that break the sections apart are called break charges.

Next, we'll look at how fireworks explode in various patterns during a display.

Fireworks Displays

­T­he pattern that an aerial shell paints in the sky depends on the arrangement of star pellets inside the shell. For example, if the pellets are equally spaced in a circle, with black powder inside the circle, you will see an aerial display of smaller star explosions equally spaced in a circle. To create a specific figure in the sky, you create an outline of the figure in star pellets, surround them as a group with a layer of break charge to separate them simultaneously from the rest of the contents of the shell, and place explosive charges inside those pellets to blow them outward into a large figure. Each charge has to be ignited at exactly the right time or the whole thing is spoiled.

To see how some common multibreak shells look in the sky, try the quick and easy "HowStuffWorks Field Guide to Aerial Fireworks." It's interactive, so you can click on a name and see the fireworks display that goes with it. The next time you witness a big fireworks show, you will know the names for each type of shell you see.

You can see how some of the more common multibreak shells look in the sky by clicking on the buttons in the illustration above. You can read descriptions of these shells below:

  • Palm: Contains large comets, or charges in the shape of a solid cylinder, that travel outward, explode and then curve downward like the limbs of a palm tree
  • Round shell: Explodes in a spherical shape, usually of colored stars
  • Ring shell: Explodes to produce a symmetrical ring of stars
  • Willow: Contains stars (high charcoal composition makes them long-burning) that fall in the shape of willow branches and may even stay visible until they hit the ground
  • Roundel: Bursts into a circle of maroon shells that explode in sequence
  • Chrysanthemum: Bursts into a spherical pattern of stars that leave a visible trail, with an effect somewhat suggestive of the flower
  • Pistil: Like a chrysanthemum shell, but has a core that is a different color from the outer stars
  • Maroon shell: Makes a loud bang
  • Serpentine: Bursts to send small tubes of incendiaries skittering outward in random paths, which may culminate in exploding stars

For more information on fireworks and related topics, check out the links on the next page.