Black Powder

The recipe for black powder, the basic material in all fireworks, has remained the same since it was discovered in China 1000 years ago: seventy-five percent saltpeter (or potassium nitrate), fifteen percent charcoal, and ten percent sulfur. Black powder explodes at the relatively slow rate of 1/10 of a second per foot—making it a "low explosive."

Stars

Stars are the precious cargo carried by "aerial" fireworks, like this one. An unlit star isn't much to look at—just a dull black lump about the size of a jawbreaker. But appearances can be deceiving. When ignited, stars create the breath-taking flashes of color and light that elicit "ooohs" and "ahhhs" from even the most jaded spectators.

Fireworks masters, like the Grucci family of Brookhaven, NY, manufacture their creations by hand, including the hundreds of stars that go into a single firework. Carefully measured ingredients like perchlorate and black powder are mixed with binding and coloring agents: magnesium or aluminum for white, sodium salts for yellow, strontium nitrate or carbonate for red, barium nitrate for green, copper salts for blue and charcoal or other forms of carbon for orange. The result is a huge slab of dough, which is then cut like a tray of brownies into half inch cubes, that are then set out to dry. (Go to our Hot Science "Pyrotechnics: It's Elemental," and discover which elements of the Periodic Table are behind the beauty and power of fireworks).

Stars can be extremely dangerous if not handled and stored with care. A sharp blow can detonate one. Oil from nearby machines can combine with certain chemicals to create an explosive gas. Even synthetic clothing, which generates static electricity, can create sparks capable of detonating the fragile shells. Firework makers must stick to wearing cotton—all the way down to their underwear.