How fireworks get their colors (and why blue is the hardest)

Every firework color comes from a metal. Strontium makes red, barium makes green, and copper makes blue. When heated, these materials give off light in different colors.

01The color is baked into the "stars"

Inside an aerial shell are small pellets called stars. Each star is a little recipe: fuel that burns, an oxygen-giver so it burns fast and bright, a binder to hold it together, and the colorant — a metal salt. When the shell bursts open high in the sky, the stars ignite and fly outward. Every streak of light you see is one star burning its color as it goes.

02Which metal makes which color

Here is the cheat sheet pyrotechnicians everywhere work from:

• Red — strontium salts (lithium gives red too)
• Orange — calcium salts
• Yellow — sodium compounds
• Green — barium compounds, with a little chlorine in the mix to sharpen the color
• Blue — copper compounds, also with chlorine's help
• Purple — strontium and copper together: red plus blue in one star
• Silver and white — magnesium, aluminum, or titanium burning white-hot
• Gold — glowing sparks of charcoal or iron

In simple terms, heat makes the metal atoms release light. The material used decides the color.

03Why blue is the hardest color in fireworks

Blue is difficult because copper needs a narrow temperature range. If it is too cool, the blue looks weak. If it is too hot, the blue breaks down. Copper's blue starts to fade at about 1,000°F (540°C), while strontium red can handle more heat.

04How gold and silver sparks work

Colored stars work like colored flames. Gold and silver work like embers from a bonfire. The long golden trails of a willow are tiny bits of charcoal or iron glowing as they fall, and bright silver comes from flakes of aluminum, magnesium, or titanium burning white-hot. That is also why golds linger and cascade while colors flash and fade — an ember keeps glowing all the way down.

05Fireworks colors are brighter than they used to be

You are not imagining it. In the 1830s, makers in southern Italy began pairing metal salts with chlorine-rich ingredients and a new, hotter-burning oxidizer, and fireworks colors turned deep and bright for the first time. In recent decades, an aluminum-magnesium alloy called magnalium pushed them further still — chemists describe modern colors as almost fluorescent. Cleanliness matters too: even a trace of stray sodium floods a star with yellow and muddies every other color, so a careful mixing room shows up in the sky.

06What to watch for at the next show

Color chemistry is more fun when you can spot it live. At your next town fiesta, Media Noche countdown, or pyromusical, try this:

1. Watch a peony or chrysanthemum burst and count the colors. If a burst changes color midair, that was a layered star burning from its outer layer to its core.
2. Catch a willow or kamuro and enjoy the long golden hang time — that is the ember trick.
3. Follow a crossette as each star splits into smaller bursts.
4. Then hunt for the rare ones: a true deep blue, or a rich purple, which means the maker landed blue and red in a single star.

We make all of these in-house — chrysanthemums, peonies, willows, palms, crossettes, kamuros, comets, Roman candles, and fountains — and you can see the lineup on our products page. And to take the colors home, our guide to photographing fireworks can help.

For a fiesta, debut, or New Year countdown, tell us about your event. We usually reply within one working day.