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!
Click on this image to see a short fireworks display (1.5 MB).
Have you ever wondered how this magic works? What is launched into the sky to make these beautiful displays?Now, you will learn all about aerial fireworks.
Firecrackers have been around for hundreds of years. They consist of black powder (also known as gunpowder) 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:
Iron or steel powder
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. See
this page for a good explanation of the chemistry and physics of color in fireworks.
These are small shells, about the size of a peach, that you can buy at roadside stands in some states. The sphere is the shell, and the small cylinder below is the lifting charge that shoots it out of the launch tube. The green fuse lights the lifting charge, which in turn lights the shell's fuse. Shells that you see at a show are typically the size of a cantaloupe or even larger.
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 bursting 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 contents of the shell 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 (several of the links below list dozens of recipes for different types of stars), 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 black powder, 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.