If you were anywhere in the US this past weekend, you were probably surrounded by the deafening booms and sparkling lights of fireworks. Humans have been in awe of these displays for almost two-thousand years, and have interwoven them into their traditions and made them the highlights of celebrations around the world. But what is it about their reactions that make them shine so brightly?
The modern aerial firework is primarily composed of a shell that contains four distinct parts. First is the container, typically composed of paper, string, and some form of fuel, typically black powder, that has been formed into a cylinder or ball. Next are the pyrotechnic stars. These are pellets containing metal powders, salts, or other compounds that when ignited burn a specific color or make a spark effect. These compounds are then combined with an oxidizer, which helps the fuel burn more quickly enhancing the explosion. At the center of the shell is the bursting-charge, a firecracker-like object which creates the initial explosion igniting the surrounding stars. Lastly is the fuse, which is directly connected to the bursting charge and provides the time delay so that the firework explodes at the right time and height.
The color and light of a firework is determined by the chemical composition of the pyrotechnic stars in the container. When the bursting-charge explodes, a rapid release of energy takes place igniting the stars within. This excites the electrons in the metal salts causing their electrons to jump to a higher orbital. As they return to their ground state, their energy is released as photons of specific energy which can then be observed in the visible light spectrum. Because specific elements have a defined emission spectrum, the color of the explosion can be directly selected for. A few of these metal/color combinations are: copper for blue, strontium for red, calcium for orange, sodium for yellow, magnesium for white, and barium for green.
The next time you watch a fireworks display, try keeping track of the elements that are used in each explosion and the amazing feat of centuries of chemistry happening above you.