Colors are created using different chemicals that burn or glow with various wavelengths. Here are some examples:
Red: strontium salts, lithium salts
Orange: calcium salts
Yellow: sodium compounds
Green: barium compounds
Blue: copper compounds
Silver: burning aluminum, titanium, or magnesium
Pure colors call for clean ingredients. Even tiny quantities of sodium impurities will create yellow or orange and mask or change other colors. If too much smoke is produced, that can also hide the colors. The cost and age of the chemicals as well as the manufacturer’s expertise greatly influence the quality of the show.
Chemistry buffs might enjoy this interactive Periodic Table of Fireworks Elements.
The different shapes in aerial fireworks are created by the arrangement of pellets (called “stars”) of explosive and color chemicals in the shells fired into the air. For example, if the pellets are equally spaced in a circle, with explosive black powder inside the circle, you will see an aerial display of small explosions equally spaced in a circle.
More complex shells explode in multiple stages and are called multibreak shells. Sometimes they contain explosives designed to create sound effects such as crackles or whistles. The sections of a multibreak shell are lit by different fuses, with the explosion of one section igniting the next. The shells are assembled so that each section bursts in sequence to produce different shapes.
To see how some common multibreak shells look in the sky, try this interactive "How Stuff Works Field Guide to Aerial Fireworks". You can click on a name (such as “willow” or “palm”) and see the fireworks display that goes with it.
Here are some other links with explanations about fireworks:
-from Drexel University
-from the University of Wisconsin-Madison
Have a fun but SAFE Fourth of July!
[photo copyright Amanda (the librarian) - all rights reserved]