One of the reasons fireworks are such magnificent things is the colours. There is just something quite extraordinary in a black night sky and bursts of purple, white, red and blue. What’s the secret behind the colours in fireworks?
It’s all in the chemistry
The answer is, of course, chemistry. Each firework contains a mixture of chemicals that not only cause the explosions and effects but also affect the colours you see. Figuring out the right combinations can be tricky and the fireworks you buy from our store are the result of experiments with different mixtures to produce high-quality, beautiful fireworks.
Now, each firework has an aerial shell that contains these chemicals. The aerial shell is essentially a tube, which contains the gunpowder and small modules known as stars. These stars are small – around 1 to 1.5 inches in diameter – but they provide a mixture of ingredients to create the effects and colours. The stars contain four ingredients:
- The fuel
- An oxidising agent
- A binder
- Metal salts or metal oxides
It’s about the release of energy
When you light up the firework, it will explode and release the stars in different directions. When the firework explodes, the ingredients in the stars are exposed to fire. This heats these elements, with the fuel and the oxidising agents speeding up the process.
This rapid release of heat will, in turn, activate the metal containing salts and oxides and create the different hues. The metal compounds absorb energy when they are heated and this causes the electrons in the material to rearrange. The rearrangement happens by moving the electrons from the lowest energy state to a higher state. Once the electrons start plummeting back down to the lower state, the excess energy is released as light.
The reason you see different colours is down to chemical elements containing different amounts of energy. With different energy, the light will emit in a different wavelength and this will determine which colour you see.
There are two mechanisms at work when the chemicals heat. The first is incandescence, which is light produced from heat. This just means that when the chemicals are hot they start glowing and emitting light. The second mechanism is luminescence, which means the light comes from the energy and not the heat itself.
Chemicals for different firework colours
So what kind of different chemicals do you need to produce the colours? Here are the chemical compositions of some of the best firework colours:
- Red – strontium salts, lithium salts
- Gold – incandescence of iron, charcoal, or lampblack
- Yellow – sodium compounds
- Green – barium compounds, chlorine producer
- Blue – copper compounds, chlorine producer
- Purple – mixture of strontium and copper compounds
- Silver – burning aluminium, titanium or magnesium powder
Fireworks are wonderful things and the colours definitely add to the appeal. They also allow you to be playful with the fireworks – choosing red for Christmas or green for St Patrick’s Day. Next time you light up fireworks pause for a moment to marvel at the chemistry behind what you see.
