## How do fireworks work? A pyrotechnics chemist explains the
science behind the brilliant colors and sounds
By Paul E. Smith, Lecture Demonstrator for Chemistry, Purdue
University
This was first published at The Conversation here:
https://theconversation.com/how-do-fireworks-work-a-
pyrotechnics-chemist-explains-the-science-behind-the-
brilliant-colors-and-sounds-173576
It is under Creative Commons 4.0 Attribution, No Derivations.
Disclosure statement
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 manufacture fireworks.
====
For many people around the world, the very 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 pale blues, there are thousands of variations
of fireworks and an entire branch of chemistry that explores
these fun explosions.
I’m a chemist and president of the Pyrotechnics Guild
International, an organization that promotes the safe use
of fireworks and their use to celebrate holidays like the
New Year.
There are hundreds of chemical formulas – or as I like
to think of them, pyrotechnic recipes – for fireworks.
These recipes are still
based off an ancient mixture of chemicals that produces
the quintessential bang, but modern fireworks use all sorts
of chemical magic to put on the incredible shows of today.
Black powder, or gunpowder, is the main ingredient of
all fireworks.
# 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 been virtually unchanged
in the centuries since. To make black powder, all you need
to do is mix 75%
potassium nitrate, 15% charcoal and 10% sulfur. To make
a basic firework or fire cracker, you just put this powder
in a container,usually made of thick cardboard or paper.
The oldest recorded recipe for black powder is from A.D.
1044 China.
Black powder is used to launch the firework in the air
as well as ignite and propel the effects – like color –
into a pattern in the sky.
So how does it work?
Once lit with a fuse or spark, the sulfur melts first at
235 F (112.8 C). The sulfur flows over the potassium
nitrate and charcoal, which then burn. This combustion
reaction quickly produces a large amount of energy and gas –
in other words, an explosion. If there is a small hole for
the gas to escape, the reaction launches the firework into
the air. In a very confined space, it blasts the components
of the firework apart and ignites everything nearby.
In addition to changing how confined the black powder
is, changing the size of the granules of powder can change
how fast it burns, too.
Think about a campfire. When you add a large tree limb
the flames burn longer and slower. If you toss 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.
Adding different elements to a mixture can produce
different colored fireworks.
# Different chemicals for different colors
If you put very fine black powder 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’re really
doing is putting energy into the electrons of that
material’s atoms. If you excite the electrons enough,
when they fall back to their normal energy levels they
release that excess energy as light.
There are a number of different elements that, when
added to a firework and heated, release different
wavelengths of light that appear as
different colors. Strontium makes red. Barium produces
green. Copper burns blue, and so on.
Making fireworks that produce blues has long been a
challenge for fireworks chemists. Deep blues are too dark
and can’t be seen against the night sky. But if the blue is
too light, it appears white. So the wavelength of the
“perfect blue” has to be very precise. This is hard to
achieve because blue light has a shorter wavelength –
meaning the distance between the peaks and valleys of the
wave of light are very close together.
Certain elements produce different colors, but what
about sparkles and flashes? To make these effects, various
metals can be added to the
pyrotechnic formulas. Aluminum, magnesium and titanium
all produce white sparks. By adding iron you get gold
sparks. Mixing in various types of charcoal can produce red
and orange sparks. Each of these elements burns at a
different speed and in a different way and so produces
varying colors and intensities of light.
Special formulas and rocket shapes can produce sound
effects like whistles.
# Making a whistle or a boom
The final piece of a good firework 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 exit through it will produce a whistling
sound. The velocity of the gas and size of the opening will
vary the pitch and sound of a whistle.
Making a boom is much easier. 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.
As you watch the fireworks this New Year’s Eve or
launch some of your own in the backyard, you’ll now know
how they work. Fireworks are a lot of fun, but the
explosions and burning chemicals are dangerous – even if
they do come in colorful packaging. If you can legally
launch consumer fireworks in your town, please handle them
properly.
