Pyrotechnic star

Pyrotechnic stars are pellets or simply pieces of pyrotechnic composition which may contain metal powders, salts or other compounds that, when ignited, burn a certain color or make a certain spark effect. They are a part of all projectile-type fireworks. The most common is the aerial shell. When watching this firework, it will launch into the sky, burning a lifting charge. Once the shell has attained proper altitude, due to other mechanisms within the firework, it will ignite the stars.

Stars are either rolled, pumped or cut.

The stars are allowed to dry for some days before being put into the fireworks piece.

Priming the stars is often necessary because they may be hard to ignite. Priming consists of coating the surface of the star with a more easily ignited substance, such as black powder.

Stars can be used in aerial shells, Roman candles, star mines, and certain bottle rockets. When used in aerial shells, the stars may sometimes be required to be "primed" with an ignition coating, consisting of a pyrotechnic mixture with an ignition temperature lower than that of the star. This is usually done if the star composition does not ignite easily.

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Wikipedia