Fireworks have changed a great deal in the 1,000 years since they were first developed in China. The primary chemical component in nearly all fireworks is “black powder.” The recipe for black powder, a mixture of 75 percent saltpeter (potassium nitrate), 15 percent charcoal, and 10 percent sulfur, originated in China about 1,000 years ago with a slightly different proportion of ingredients. Black powder has been used in loud and fiery displays ever since–first to ward off evil spirits, and later to entertain and celebrate. Today’s fireworks rely on black powder for two critical functions. Gas released when the powder combusts first propels the firework skyward and later blasts its contents outward into the elaborate patterns that spectators come to see.