It is thought that fireworks were first developed in China around the second century, B.C. Historians believe the first natural “firecrackers” were actually made of bamboo stalks that were thrown into a fire and would explode due to the overheating of the air pockets in the bamboo.
Centuries later, between 600-900 AD, according to legend, a Chinese alchemist mixed sulfur, potassium nitrate, and charcoal to produce the earliest known form of “gunpowder”. This mixture was poured into hollowed-out bamboo sticks—later it would be stiff paper tubes—thus making the first “man-made” fireworks.
Firecrackers basically have the same chemical composition as they did thousands of years ago, although some firecrackers today may contain aluminum instead of or in addition to charcoal to make the explosion brighter.
Fireworks often contain aluminum, iron, steel, zinc, or magnesium dust to create bright, glimmering sparks. The powdered metals heat up until they burn or glow brightly. An assortment of chemicals can be used to create colors.
Sparklers work a little differently. A sparkler burns over an extended period of time and produces inordinately bright and sparkling showers of light.
A sparkler contains fuel, an oxidizer (defined as “a substance that initiates or promotes combustion in other materials;” potassium nitrate is a common oxidizer), iron or steel powder, and a binder such as sugar or starch.
These compounds, which are in the proper proportions to prevent an explosion. form a sludge that can coat a wire (by dipping it) or by pouring it into a tube. Once this ooze dries, it becomes a sparkler. When lit, the sparkler burns from one end to the other in the same way a cigarette would.
Aerial fireworks are the mainstay of fireworks shows and are typically composed of the following:
- Mortar: the tall cylinder that holds the shell until it is launched.
- Shell: Usually a paper sphere packed as two halves and is filled with stars designed to produce a specific visual effect.
- Fuse: The fuse is lit which provides heat to ignite the black powder.
- Lift charge: This black powder charge found at the bottom of the shell ignites and propels the shell out of the mortar.
- Black powder: a form of gunpowder formulated with 75% potassium nitrate (saltpeter), 15% charcoal, and 10% sulfur.
- Timed fuse: This fuse ignites the burst charge.
- Burst charge: Located in the middle of the shell, ignites the stars in the shell.
- Stars: When ignited, they create the firework’s special sound and light effects. The stars inside fireworks are made of powdered combinations of metal and other chemical components, called metal salts. When ignited, the metal particles absorb an enormous amount of energy. As they start to cool, the particles emit energy in the form of light. The color of this light is dependent on the type of metals used. Strontium produces the color red, calcium produces orange, sodium produces yellow, barium produces green, copper produces blue, strontium and copper produce purple, and magnesium or aluminum and titanium produce white.
Some stars contain compounds that create special sound effects. For example, potassium chlorate produces a louder sound, bismuth, on the other hand, causes a crackling or popping sound. Other chemicals can be tightly packed into a tube in order to provide a slow burn. The slowly released gas creates a whistling sound.
There are also multi-break shells, which burst in two or three steps. They may be constructed as a shell with other shells inside it, or they may contain several sections The sections are ignited by different fuses. As one section bursts, a break charge ignites the next section. The pattern an aerial shell produces depends on the star pellets arranged inside the shell.
Now, the next time you watch an aerial display you’ll know how the pyrotechnics create a spectacular show of light and sound.
