As far back as the tenth century the Chinese were making fireworks, using saltpeter, sulfur, and charcoal. With the invention of gunpowder (which is actually composed of those same ingredients), the manufacture and display of fireworks came under military control in Europe until the eighteenth century, when the Italians, notable enthusiasts of fireworks, took the lead in using them at festivals and celebrations. (Today the rapid fire of dizzying rockets and pinwheels reflected in the canals near Venice’s San Marco each July in celebration of the Feast of the Redeemer surpasses any show here on the Fourth.) The nineteenth century brought some stupendous shows in England, initiated by the shows at the Crystal Palace near London using lances, or tiny, brightly burning tubes, to trace out words, pictures, and portraits of famous people-with some 35,000 lances per piece.
Fireworks contain excess fuel so that after the initial blast, some remains to burn in the air. Most are made of potassium nitrate, sulfur, and finely ground charcoal. Others contain potassium nitrate and salts of antimony, or arsenic and sulfur. Gunpowder provides the lift and explosion, and potassium chlorate creates brilliant colors. The different patterns created by fireworks in the air are determined by variations in composition, arrangement, and casing. Roman candles, for example, packed in a case ¾ inch in diameter, have three layers, each with three different types of material: a “fountain” charge of sulfur, charcoal, saltpeter, and other metal particles that give off sparks; “stars” – white or colored compounds that burn for a few seconds; and gunpowder.
In each layer the fountain burns and lights the star, which is shot out by the gunpowder. Other types, such as shells that are filled with stars, have smaller shells inside that produce successive blasts after the first. The casing for pinwheels has a nozzle at each end and a central nail around which the explosive material revolves. Rockets have a paper cap on a cylindrical case tightly packed with stars and gunpowder. When the fuse is lit, burning occurs in a lower conical cavity. A propelling charge sends the rocket soaring then ignites the gunpowder and stars for a breathtaking spectacle in midair.
From: How Do They Do That?
By: Caroline Sutton