Roman Candle (firework) - Construction and Ignition

Construction and Ignition

A Roman candle is a firework constructed with bentonite, lifting charge, pyrotechnic star, black powder, and delay charge. 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 (3") 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.
• Roman Candles are illegal to set off in some states in the U.S.