How do fireworks work? A pyrotechnic chemist explains the science behind the amazing colors and sounds

For many people around the world, the first moments of the new year will be filled with the sounds and colorful light shows of fireworks. From loud bangs to long whistles, bright reds to bright blues, there are thousands of variations of fireworks and a whole branch of chemistry that explores these fun explosions.

I am a chemist and president of the Pyrotechnics Guild International, an organization that promotes the safe use of fireworks and their use to celebrate holidays such as New Years.

There are hundreds of chemical formulas – or as I like to think of them, pyrotechnic recipes – for fireworks. These recipes are still based on an ancient mix of chemicals that produce the basic bang, but modern fireworks use all kinds of chemical magic to put on today’s incredible shows.

A pile of shiny black powder and a jar.

It all starts with black powder

The first ingredient of any firework is the ancient explosive black powder. It was discovered by Chinese alchemists more than a thousand years ago, and the recipe has changed little over the centuries. To make black powder, simply mix 75% potassium nitrate, 15% charcoal and 10% sulphur. To make a basic firework or firecracker, simply put this powder in a container, usually made of thick cardboard or paper.

A parchment of Chinese characters.A parchment of Chinese characters.

Black powder is used to send the firework into the air as well as to ignite the effects – such as color – and drive them into a pattern in the sky. So how does it work?

When ignited with a fuse or spark, sulfur first melts at 235 F (112.8 C). The sulfur flows over the potassium nitrate and charcoal, which then burn. This combustion reaction produces a large amount of energy and gas quickly – in other words, an explosion. If there is a small hole for the gas to escape, the reaction sends a firework into the air. In a very confined space, it explodes the components of the firework apart and ignites everything nearby.

In addition to changing how limited the black powder is, changing the size of the powder granules can change how quickly it burns, too. Think of a campfire. When you add a large tree limb to the flames burn longer and slower. If you throw a handful of sawdust into the flame it burns hot and fast. Black powder works similarly, and this makes it easy to control how much and how fast energy is released.

A mix of red, yellow and green firework explosions.A mix of red, yellow and green firework explosions.

Different chemicals for different colors

If you put a very fine black powder in a confined space it explodes in a cloud of heat, gas and noise. So where do the colors and bright light come from?

When you heat up any material, what you are really doing is putting energy into the electrons of the atoms of that material. If you excite the electrons enough, when they fall back to their normal energy levels they release that extra energy as light.

There are several different elements that, when added to a firework and heated, emit different wavelengths of light that appear as different colors. Strontium makes red. Barium produces green. Copper burns blue, and so on.

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Making fireworks that produce blues has long been a challenge for fireworks chemists. Deep blues are too dark and cannot be seen against the night sky. But if the blue is too light, it seems white. So the wavelength of the “perfect blue” must be very precise. This is difficult to achieve because blue light has a shorter wavelength – meaning that the peaks and valleys of the light wave are very close together.

Certain elements produce different colors, but what about sparkles and flashes? To produce these effects, various metals can be added to the pyrotechnic formulas. Aluminum, magnesium and titanium produce a white spark. By adding iron you get gold sparks. Mixing in different types of charcoal can produce red and orange sparks. Each of these elements burns at a different speed and in a different way and therefore creates different colors and intensities of light.

Making a whistle or boom

The final piece of good fireworks is an exciting sound effect.

To add sound effects to fireworks you need a formula that produces a large amount of gas very quickly. If a firework has a small opening for the gas to pass through, there will be a whistling sound. The velocity of the gas and the size of the opening will change the height and sound of the whistle.

It’s much easier to make a boom. You simply put an energetic formula in a confined space with nowhere for the gas to go. When ignited, the pressure will build and the firework will explode, producing a sudden boom or bang.

When you’re watching the fireworks on New Year’s Eve or launching some of your own in the backyard, you’ll now know how they work. Fireworks are fun, but the explosions and burning chemicals are dangerous – even if they come in colorful packaging. If you can legally launch consumer fireworks in your home, please handle them properly.

This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Paul E. Smith, Purdue University

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Paul E. Smith is president of the Pyrotechnics Guild International, Inc. He is a member of the American Pyrotechnics Association, the National Fireworks Association, and the International Pyrotechnics Society. He has a license from the BATFE to make fireworks.

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