Everyone loves to watch a firework display on the Fourth of July. However, if there were no bright colors (blues, greens, reds, etc.) it would not be nearly as fun. Instead of ooh’s and aah’s, you would probably hear umm and hmm.
Black powder is a main component in fireworks, but it gives off only one color, bright yellow. Therefore, pyrotechnicians (not to be confused with pyromaniacs who burn many things besides fireworks and without the owners’ permission) must have a knowledge of chemistry to make fireworks that produce a variety of colors.
The bright colors that you see in fireworks are produced by burning metal salts. Pyrotechnicians put these metal salts into stars (not to be confused with movie stars, although movie stars have been known to be colorful also when heat was applied). The stars are arranged in specific shapes within the fireworks’ shell. When this shell explodes, the stars are distributed into the sky. These stars, which contain fuel, oxidizer, color-producing chemicals, binder and a chlorine donor (not to be confused with a blood donor, although one could be needed if you get too close to the fireworks) are responsible for the fireworks’ appearance. The atoms in the metals that are contained in the stars cause light to be emitted at high temperatures. The light gives off the particular characteristics of the metal that is used.
Pyrotechnicians know which substances produce which colors (they are the people who were paying attention in chemistry and physics class). For example, sodium salts produce yellow, lithium compounds produce red, copper salts produce blue and green, etc. However, the colors in fireworks are determined by more than just the metallic substance used. For example, calcium (not exciting by itself) gets really excited when it is around other substances, thus enhancing the color (sort of like being in a room by yourself, and then Johnny Depp walks in). Metallic fuels are usually chosen over organic fuels as organic fuels cannot generate as high temperatures.
To produce pure colors you must have pure ingredients (like your mom always said, you can’t make a silk purse out of a sow’s ear). Some elements will wash out colors and, therefore, must be kept out of the mixture. Commercial fireworks use only a small amount of compounds to make all the colors of the spectrum. Although pyrotechnicians have mastered producing yellow, orange, blue, red and some greens, they are still working on producing a deep forest green.
Next time you are watching a fireworks display and admiring the brilliant colors, just remember that it could be you putting on the show if only you hadn’t been painting your nails during chemistry class.