Human World

How do fireworks get their beautiful colors?

Pink sky with many streaks of yellow in the middle.
View at EarthSky Community Photos. | C. Gentile from Florham Park, New Jersey, captured this image of the 4th of July celebration and wrote: “The sky was really this color!” Thank you. And happy 4th of July to all who celebrate it.

The U.S. has a big holiday today – Independence Day – aka the 4th of July – on July 4. And that means it’s fireworks season!

If you watch your local fireworks display, you’ll see the reds, oranges, yellows, greens, blues and purples exploding in the skies. You’ll hear lots of “ohhhhs” and “ahhhhs,” to be sure!

But what creates the colors of fireworks?

What creates the colors in fireworks?

The colors in fireworks come from a simple source: they are pure chemistry. Essentially, they’re created by the use of metal salts. Naturally, these salts are different from table salt, and chemistry ‘salt’ refers to any compound that contains metal and non-metal atoms. And some of these compounds produce intense colors when they burn, which makes them ideal for fireworks.

Others, like potassium nitrate, sulfur and charcoal are useful to help the fireworks burn. While nitrates, chlorates and perchlorates provide oxygen for the combustion of the fuel. Dextrin, often used as a starch, holds the mixture together. In addition, the use of chlorine donors strengthens some colors.

Metal salts commonly used in firework displays include: strontium carbonate (red fireworks), calcium chloride (orange fireworks), sodium nitrate (yellow fireworks), barium chloride (green fireworks) and copper chloride (blue fireworks). Purple fireworks are typically a mixture of strontium (red) and copper (blue) compounds.

Then they pack these metal salts into small pea- to plum-sized pellets called “stars” or pyrotechnic stars.

People and fireworks at the park under the harvest full moon.
View at EarthSky Community Photos. | Walter Karling in Kissena Corridor Park, Flushing (Queens), New York City, New York, captured this wide-angle photo of people and fireworks under the harvest full moon sky, together with Jupiter and Saturn, on September 18, 2021. Thank you, Walter!

What happens after fireworks ignite?

After a firework ignites, a lift charge propels it into the sky. That’s just explosive black powder in a confined space that, when lit, causes a fast increase of heat and gas that can send a firework as high as 1,000 feet (300 meters) into the air.

Meanwhile, a time-delay fuse burns slowly into the interior of the firework shell. Then, after about five seconds, as the shell is soaring overhead, the fuse kindles a charge that reaches the core of the firework, explodes and ignites the stars that contain the metal salts.

Voila! A beautiful and colorful fireworks display.

Word of caution

By the way, the people who create fireworks are precise, expert craftsmen. Putting on a fireworks display is a complex process, and done safely in a controlled environment. If even one thing is off – too much black powder, stars that aren’t aligned correctly or a trigger that fires too soon or too late – everything can go kaboom. After all, fireworks are explosives, and working with them is best left to the professionals.

Of course today, some firework displays are done with drones.

Waning gibbous moon over night cityscape with fireworks.
View at EarthSky Community Photos. | Ken Chan captured this image at last year’s 4th of July celebration in San Francisco, California (July 4, 2023). He wrote: “July 4th as celebratory fireworks erupted throughout the city.” Thank you, Ken!

Bottom line: Basically, the red, orange, yellow, green, blue and purple colors exploding in the night sky during a fireworks festival are created by the use of metal salts.

Read more: The Chemistry of Fireworks Colors

Read more: The Chemistry of Fireworks

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July 4, 2024
Human World

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