firework

fireworks

[fahyuhr-wurk]

Explosives or combustibles used for display. Of ancient Chinese origin, fireworks evidently developed out of military rockets and explosive missiles and accompanied the spread of military explosives westward to Europe in the Middle Ages. In force-and-spark compositions, potassium nitrate, sulfur, and ground charcoal are used; additional ingredients produce various types of sparks. In flame compositions, such as the stars that shoot out of rockets, potassium nitrate, salts of antimony, and sulfur may be used; for coloured fire, potassium chlorate or perchlorate is combined with a metal salt that determines the colour. Rockets are lifted by recoil from the jet of fire thrown out by the burning composition.

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Roman candle is a traditionally type of firework, that ejects one or more stars or expolding shells.

Roman candles come in a variety of sizes, from small 6 mm (1/4") diameter for consumers, and up to 8 cm (3") diameter in professional fireworks displays

Roman candles are banned in some countries due to their disposition to cause accidents.

Construction and ignition

A Roman candle is a firework constructed with bentonite, lifting charge, pyrotechnic star, black powder, and delay powder. The device is ignited from the top. The delay powder is packed tightly in the tube, so that the flame cannot reach around the sides of the plug of delay composition. It therefore burns slowly; as it is consumed, the flame moves down through the tube. When the flame reaches the topmost pyrotechnic star, the star is ignited. Because the star fits loosely in the tube, the fire spreads around it and ignites the lift charge. The lift charge burns quickly, propelling the star out of the tube, like a bullet from a gun. In doing so it also ignites the layer of delay powder beneath it, and the process repeats. There are several variations on this:

  • Many Chinese Roman candles use clay instead of delay powder and run a length of fuse down the inside of the candle to time the lifts.
  • Larger Roman candles will usually add more lift to the highest layers and less to the lower layers in order to cause the stars to lift to the same altitude. This is due to the shorter length of tube available for accelerating the higher stars (see firearms internal ballistics).
  • Some very large candles will load comet shells instead of stars.

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