Shells
Robert Noyce, Deseret Morning News Contrary to popular belief, fireworks are not rockets but shells that are propelled with black powder from steel tubes (mortars).
Round shells contain a single display, such as a chrysanthemum, waterfall or ring pattern.
Cylindrical shells (multibreak) contain multiple displays that can produce more random pattern and colors. Some shells can have up to 16 effects.
Screeching and whistling noises are produced by a substance that oscillates as it burns.
Multibreak fireworks contain several cardboard compartments. Bursting charges in each compartment ignite and propel stars through the air.
The more resistant the cardboard compartment is to the explosion, the larger the display.
Explosive sounds are created by placing a sound charge in the shell. This is achieved by adding a mixture of perchlorate to the shell.
Patterns are determined by how stars are positioned in the shell.
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