Fireworks work via complicated processes and are far more intricate in their design that you might readily give them credit for, requiring a full understanding of physical and chemical science. Utilising not only propellants and special effects but also oxygen-producer, fuel, binder and colour producer in order to give the light explosion (known as ‘stars’) their appearance.
So what types of elements are responsible for the colours of fireworks? Well those would be the ‘colour producers’. These work through two different mechanisms – incandescence and luminescence. Incandescence describes light that’s caused from heat. This heat changes the colour of the light – starting through infrared then travelling through red, orange, yellow and white light as the temperature increases. By controlling the temperature of the explosion then it is possible to control its colour through the use of charcoal and similar components that will glow appropriately. This can be achieved by including aluminium, magnesium and titanium – each of which burns very brightly and so can be used to increase a firework’s temperature.
Luminescence meanwhile describes light that comes from other energy sources (as opposed to heat) which gives it its moniker ‘cold light’. Cold light can be produced at room temperature or cooler (and so is also used in indoor fireworks – remember those?). Here energy is absorbed by the electron of an atom or molecule then released in the form of a ‘photon’ (the wave particle that makes up light). This can be achieved via various salts, though some such as barium chloride (which glows green) are unstable at room temperature. Barium is therefore combined with chlorinated rubber (under high temperatures) to keep it more stable by creating ‘barium chloride’.
Some Luminescent materials however mustn’t get too hot such as copper (which gives off blue light). In these cases it’s important for the firework to stay fairly cool while being bright enough to be seen. As you can see then it is a very delicate balance and complex process which all takes place in a relatively small space (the body of the firework). It is not merely a matter of controlling what types of elements are responsible for the colours of fireworks, but also what temperatures and how the elements interact.
Quality however is also an issue, and only pure ingredients will create pure looking colours. Trace amounts of sodium can add yellow-orange to the colours scene and alter their appearance. Similarly smoke or residue can mask the colour of the firework so these too need to be kept to a minimum. When picking a firework be sure to check the manufacturer and the date of the firework.
So now you know what types of elements are responsible for the colours of fireworks.