It's also one of the year's most spectacular displays of science in action. The insights are adapted from science demonstrations they present to high-school students across North Carolina each year through NC State's Science House learning outreach program. Colors are produced when gunpowder packed inside the firework explodes, creating temperatures high enough to burn metallic salts also contained within the firework.
Different salts give off different colors when they burn.
Lithium, for instance, gives off a vibrant red, copper creates blue-green and sodium burns a brilliant yellow. Fireworks that produce multiple colors or effects are divided into several stages, sort of like a multi-stage rocket. The stages are packed with different chemicals to create whichever colors and effects are desired. Each stage is separated by small spaces that can be connected by little fuses, so the effects can be timed and ordered. It depends on how the gunpowder is packed.