Red, green, gold and blue firework bursts over a dark river at night, with a calm dark sky on one side
AI-generated image, not a photograph of a real person or place.
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THE CHEMISTRY OF A BURST

Every colour
is a metal.

RED · GREEN · BLUE each from its own metal

  • Heat lifts the electrons
  • Each metal has its colour
  • Too hot washes it out
  • Chemistry you can see from a field

A firework's colour is chosen before it leaves the ground.

Small amounts of metal compounds are packed into the shell. When they burn, heat lifts their electrons up and each metal gives the energy back as its own colour of light.

Updated

Pick a colour

THE SHORT ANSWER

Heat goes in,
colour comes out.

Firework colour is the same science as a school flame test.
Each metal glows its own colour.

THE METALS

One metal, one colour

Strontium and lithium give red, sodium yellow, barium green and copper blue. Titanium and magnesium burn silver or white.

Pick a colour

THE PROBLEM

Blue is the hardest

Copper's blue needs a hot flame, but too much heat destroys it. A deep, bright blue is still the one colour makers struggle to get.

Why blue is hard

THE PHYSICS

Light from electrons

Heat kicks electrons into higher energy levels. As they drop back to their ground state they shed the energy as light of one colour.

See the numbers

A QUICK COLOUR CHECK

Which metal
made that colour?

Pick a colour you might see in a display to find the metal usually behind it. The bar shows where that colour sits in the visible spectrum, from short-wavelength blue to long-wavelength red.

Colour check

Choose a colour
Deep redStrontium or lithium

Both give deep red flames. Science Focus notes that relatively cool-burning strontium carbonate is used for red.

OrangeCalcium

Calcium gives an orange colour. In the classroom flame test, calcium chloride burns brick red.

YellowSodium

Sodium gives yellow to orange, the same colour as sodium street lights. Science Focus names sodium nitrate as the yellow.

GreenBarium

Barium burns green, and with chlorine it gives a vivid neon green. In a flame test its apple green is short-lived.

BlueCopper

Copper compounds such as copper chloride give blue. It is the hardest colour: too little heat makes it dim, too much destroys it.

Sources: Royal Society of Chemistry, What makes the colours in fireworks? (teacher sheet); Nautilus, Fireworks Displays Can't Include a Perfect Red, White, and Blue; BBC Science Focus; NASA, Visible Light.

Colours from Royal Society of Chemistry flame-test results and Nautilus; spectrum order from NASA. Flame tests with these chemicals are for supervised labs only.

TWO NUMBERS WORTH KNOWING

Colour is
a wavelength.

One figure for the range our eyes can see,
one for the exact yellow sodium gives off.

380–700 nm

Wavelengths the human eye can detect

NASA says the eye typically detects wavelengths from 380 to 700 nanometres. Violet sits at the short end, around 380, and red at the long end, around 700.

VISIBLE LIGHT · NASA

≈ 589 nm

Sodium's two strongest lines

The US National Institute of Standards and Technology lists sodium's strongest lines at 5889.950 and 5895.924 ångströms in air: about 589 nanometres, a warm yellow.

SODIUM YELLOW · NIST

Each element's pattern of lines works like a fingerprint. NASA notes that astronomers read the same kind of patterns in the light of the Sun and stars to find which elements are there.

FOUR THINGS TO WATCH FOR

Read the sky
at the next display.

A single blue and violet firework burst glowing softly against a dark night sky
AI-generated image, not a photograph of a real person or place.

You can name the chemistry from a safe spot in the crowd. These are the colours and the metals usually behind them.

  1. Name the yellow

    A warm yellow-orange is sodium, the same colour the RSC flame test compares to street lights.

  2. Spot the reds

    Deep reds come from strontium or lithium; a more orange red points to calcium.

  3. Judge the blue

    Notice how the blues look dimmer than the reds and greens and fade into the night sky.

  4. Follow the sparks

    Silver and white come from titanium or magnesium; gold sparks in the flame test come from iron.

WHY BLUE IS HARD

Hot enough,
but not too hot.

A Bunsen burner flame in a school laboratory turned bright crimson by a wire loop dipped in a metal salt
AI-generated image, not a photograph of a real person or place.

Raising the flame temperature makes colours brighter, but if it gets too hot the metal species giving off the colour is destroyed and the light washes out to white. Copper's blue is the most fragile, so makers aim for a narrow temperature range, often with copper chloride.

Fireworks were yellowish orange for centuries, from gunpowder alone. Italian makers added metals in the 1800s, and hotter fuels such as aluminium and magnesium later made colours far more vivid. A truly deep, bright blue has still not been found.

Questions

Questions people ask

Why do fireworks have different colours?

Metal compounds packed into the firework are heated as it burns. The heat lifts their electrons to higher energy levels, and as they fall back they give off light. Each metal gives its own colours.

Which metal makes red fireworks?

Strontium and lithium both give deep reds. BBC Science Focus names relatively cool-burning strontium carbonate as a common red.

Why are blue fireworks so rare?

Blue usually comes from copper, which needs a hot flame but is easily destroyed if it gets too hot. No one has yet found a mix that gives a blue that is both deep and bright, and blue also blends into the night sky.

How do fireworks make shapes?

The colour-making packets, called stars, are packed with gunpowder and a burst charge. At the right height the burst charge fires and throws the stars out into the planned pattern.

Can I try a flame test at home?

No. The Royal Society of Chemistry's flame test is a supervised school experiment with a Bunsen burner and eye protection, and some of the chemicals, such as barium chloride, are toxic. Watch a display instead.

Sources

Where the facts come from

  1. Royal Society of Chemistry: What makes the colours in fireworks? (teacher sheet)
  2. Nautilus: Fireworks Displays Can't Include a Perfect Red, White, and Blue
  3. BBC Science Focus: How are the colours and shapes of fireworks created?
  4. NASA Science: Visible Light
  5. NIST Handbook of Basic Atomic Spectroscopic Data: Strong lines of sodium

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