The Chemistry of Color in Fireworks
It is pretty obvious that fireworks are made of explosives but I had no idea of the chemistry involved in making colorful fireworks. Fireworks are a two-step process, propellants to put them in the air and then the points of light projected from the fireworks creating color. The points of light ejected from fireworks are called stars. Stars require an oxygen producer, fuel, a binder to keep everything where it needs to be, and a color producer. There are two types of color production in fireworks incandescence and luminescence. Incandescence is a light produced from heat. Heat causes some substances to become hot and glow. When the temperature of a firework is controlled the glow of a firework can be manipulated to a desired color temperature. Metals like aluminum, magnesium and titanium burn very brightly and are useful for increasing the temperature of a firework. Luminescence is the light produced using energy other than heat. Luminescence is referred to as cold light because it can occur at room temperature and even at cooler temperatures. Luminescence is produced when energy is absorbed by electron of an atom or a molecule causing it to become unstable and excited.
When the electron returns to a lower energy state the energy is released in the form of a photon of light. The energy of the photon determines its color. Some colors are easier to work with than others. Barium chloride makes the color green but is unstable at room temperature so barium must be combined with a more stable compound like chlorinated rubber. Copper chloride makes the color blue and is unstable at high temperatures so the firework cannot be allowed to get too hot. The most pure colors require completely pure ingredients. For example even trace amounts of sodium will create a yellow orange color and are sufficient to overpower other colors completely. The chemistry of a firework must be exact or colors will be impacted significantly. If the chemistry is off by a tiny bit too much smoke or residue will mask the color as well. Going through the rainbow of colors means careful formulation, skill of the manufacturer and expiration dates that are exact. The color red is made from lithium carbonate, orange is made from calcium salts, yellow is made from sodium compounds, green is made from barium compounds, blue is made from copper compounds added with chlorine producers and purple is made from red and blue compounds added together. Now I cannot wait for July 4th!