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Our first stop was How Fireworks Work, from Marshall Brain, mastermind of the HowStuffWorks web site. Brain presents an illustrated introduction to aerial fireworks and the pyrotechnic devices -- firecrackers and sparklers -- that make these fabulous displays possible. We learned that a firecracker consists of a paper tube tightly packed with black powder (aka gunpowder) and a fuse to light the powder. Aluminum is usually added to brighten the explosion. A sparkler consists of several compounds -- fuel, oxidizer, iron or steel powder, and a binder ingredient like sugar or starch. Mix these together with water, and you get a chemical slurry that you can pour into a tube or dip onto
a wire. When lit, the sparkler burns for up to a minute, emitting a "bright and showery" light. Fireworks often contain iron, steel, and zinc or magnesium dust added for dazzling, longer burning displays. Specific colors are created from a variety of additional chemicals. Multibreak shells burst in two or three timed phases, creating the dramatic fountains and floral patterns that always evoke appreciative "oohs" and "aahs." Next, we stopped at The Physics of Colored Fireworks, found on an enthusiast's fascinating Pyrotechnics site. The site taught us that fireworks were invented in ancient China, but rainbow colored effects are much more recent. Before the industrial
revolution, steel and charcoal created pyrotechnic showers of orange and yellow flame. Chlorates, discovered in the 18th century and developed by the chemical industry in the 19th, added reds and greens to the palette. Safe blues and purples were introduced in the 20th century. But the process is hardly as simple as adding food coloring to a recipe. The typical aerial firework is a shell that consists of four parts: - a cylindrical paper and string container
- sparkler compound shaped into a small ball or cube, known as a star
- a firecracker-like charge at the center, known as the bursting charge
- a fuse that provides a time delay so the explosion occurs at the right altitude
Specific molecules that emit light of a particular wavelength are added to the chemical
mix of the pyrotechnic stars. These molecules produce colored radiation that can be seen by the human eye. An article from About.com, "Chemistry of Fireworks Colors," describes incandescence (light produced from heat) and luminescence (cool glowing light produced when an electron releases photons), the two main mechanisms for creating colorful fireworks. The article also provides a table that shows various salts and chemical compounds and the colors they produce. Finally, don't miss the field guide to Aerial Fireworks for animated demos that will help you distinguish between the palms, rounds, rings, chrysanthemums, and willow-shapes at this year's Fourth
of July display!
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