How Fireworks Work: The fascinating science of our July 4 celebration, explained

How Fireworks Work: The fascinating science of our July 4 celebration, explained
How do fireworks get their color, exactly?
Source: Ng Han Guan/AP
How do fireworks get their color, exactly?
Source: Ng Han Guan/AP

As you watch the evening sky burst and cackle into life with glittering fireworks, do you ever wonder: How the hell did they do that?

Fireworks come from the humble “aerial shell,” a handcrafted capsule loaded with all the fixings needed to control a firework’s color, sound and shape. The shell includes an oxidizing agent, fuel, a colorant, a binder and what’s referred to as “stars” — small clusters that give a firework its color when it detonates. The stars also serve as a model for what form the firework will take once it spreads across the sky. The way fireworks are positioned within the capsule determines whether it’ll look like a smiley face, a star, a heart, a flower, etc.

The firework’s color is dependent on the chemicals used. As the Verge noted, a strontium compound yields red, a barium compound yields green, a copper compound yields blue and a sodium compound yields a yellow-orange.

When it’s showtime, someone will ignite the capsule’s center, which has a fuse. This causes the shell’s sweet ’splosion, and those mesmerizing pyrotechnics are born.