Despite their different colours, shapes, speeds and sounds, all fireworks have the same basic components. Aerial fireworks consist of a shell made of heavy paper that holds the ‘lift charge’, the ‘bursting charge’, and the ‘stars’. All of these glittery spectacles come from good old-fashioned combustion.
Combustion is a chemical reaction between two substances (a fuel and an oxidant) that produces light and heat. The heat causes gasses to expand rapidly, building pressure. The shells are tightly wrapped cylinders, which provide good resistance to this pressure, giving it a short time to build in intensity. Then, when the reaction overpowers the shell, you get the explosive firework effect.
It all starts when the shell is placed into a mortar (a cylinder the same size as the shell, which holds the firework in place while the fuse burns). The lift charge, at the bottom of the shell, is basically concentrated black powder (charcoal, sulphur, and potassium nitrate).
When lit by the dangling fuse, the lift charge sends the shell into the air. Basic firecrackers are Just paper-covered black powder: you light the fuse and listen to the popping sound. The bursting charge is another round of black powder with its own time-delayed fuse higher up in the shell. The bursting charge creates the heat to activate the stars that surround it and explode them outward from the shell. The stars are where the magic happens.
Stars are balls made up of fuels, oxidizers, colour-creating combinations of different kinds of metals, and a binder to hold everything together. The stars can be arranged within the firework shell to create shapes. The shapes can be things like hearts, stars, and circles. Hundreds of stars can be used in a single firework shell.
More complex fireworks – ones that produce a shape like a smiley face, have multiple phases of different colours, or make extra sounds like whistles, for example – have shells with a more intricate infrastructure. In these types of fireworks, there are more time-delayed fuses linked to various bursting charges with their own surrounding stars. Each of these may sit in its own individual interior shell. These are called “multi-break shells’.
While a sight to behold, fireworks are individually wrapped chemistry experiments. Tapping one too hard or creating a static electricity shock with your synthetic-material clothing could be deadly and one exploding near to your face could result in horrific burns and even blindness. They don’t have the word ‘fire’ in them for nothing.
Colours involve different measurements and combinations of oxygen producers, fuels, binders, and colour producers. You can make colour through incandescence – light created through heat (orange, red, white), or luminescence – light created from a chemical reaction without extreme heat (blue, green). It’s all about temperature control and balance.
- Orange – Calcium
- Red – Strontium and lithium
- Gold – Incandescence of iron, charcoal or lampblack
- Yellow – Sodium
- Electric white – Magnesium or aluminium
- Green – Bariumplus a chlorine producer
- Blue – Copper plus a chlorine producer
- Purple – Strontiumplus copper
- Silver – Aluminium, titanium or magnesium powder/flakes