The Periodic Table of Firework Colours
D. Indumathi, Chennai

This Deepavali, you may have lighted sparklers or exploded a firecracker, or perhaps just watched someone else doing so.
Sparklers emit showers of coloured sparks including silver and gold. Here there is a hand-held non-burning metallic rodd around which there is a combustible coating. They are made by dipping the rod in a thick solution containing various compounds and then allowed to dry. When lighted, the compounds burn, giving out coloured sparkles and also crackling noises.

How are sparklers made?
What actually allows the sparkler to burn this way? The mixture that coats the sparkler contains a fuel (for burning), and oxidiser (to provide the oxygen needed for burning), iron powder, and a binder (for keeping the ingredients together). The binder is commonly made from sugar or starch, which is sticky. The fuel is the same as in an exploding fire cracker: charcoal and sulphur. A typical oxidiser is potassium nitrate. When heated (by burning the fuel), it does not burn, but releases oxygen. This released oxygen is used to allow the fuel to continue burning in a slow, controlled fashion. The fuel and oxidiser are together called black powder.
In a firecracker, the black powder is put into a tight paper tube with a fuse to light the powder. In recent times, firecrackers are first sent into the sky, like a "rocket" and then they explode after some time. They also work the same way, but have in addition they contain cylinders containing sparkler-like material which then show up as 'stars' when they explode in the sky. There is also an initial "lifting charge" that first propels the firecracker like a rocket into the sky. A fuse provides a time delay so that the firecracker explodes only after reaching a certain height in the sky. See figure. But the biggest matter of curiosity surely is, how are all those beautiful colours produced?

The Chemistry of Fireworks
There are two main mechanisms of colour production in fireworks, incandescence and luminescence.
Incandescence is the emission of light caused by high temperature. As a substance heats up it emits colours in different stages starting with infrared, then red, orange, yellow, and white as it becomes increasingly hotter. The temperature of a firework can be controlled and with different components added such as charcoal, can be manipulated to be a desired colour at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.
Luminescence is the emission of light by a substance that has not been heated. To produce luminescence, energy is absorbed by an electron, causing it to become excited, but unstable. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The colours are produced by heating metal salts, such as calcium chloride or sodium nitrate, that emit characteristic colours.

List of colours and elements in Fireworks:
Aluminum – Aluminum is used to produce silver and white flames and sparks. It is a common component of sparklers.
Antimony – Antimony is used to create firework glitter effects.
Barium – Barium is used to create green colours in fireworks, and it can also help stabilize other volatile elements.
Calcium – Calcium is used to deepen firework colours. Calcium salts produce orange fireworks.
Carbon – Carbon is one of the main components of black powder, which is used as a propellant in fireworks. Carbon provides the fuel for a firework.
Chlorine – Chlorine is an important component of many oxidizers in fireworks. Several of the metal salts that produce colours contain chlorine.
Copper – Copper compounds produce blue colours in fireworks.
Iron – Iron is used to produce sparks. The heat of the metal determines the colour of the sparks.
Lithium – Lithium is a metal that is used to impart a red colour to fireworks. Lithium carbonate, in particular, is a common colourant.
Magnesium – Magnesium burns a very bright white, so it is used to add white sparks or improve the overall brilliance of a firework.
Oxygen – Fireworks include oxidizers, which are substances that produce oxygen in order for burning to occur. The oxidizers are usually nitrates, chlorates, or perchlorates. Sometimes the same substance is used to provide oxygen and colour.
Phosphorus – Phosphorus burns spontaneously in air and is also responsible for some glow-in-the-dark effects. It may be a component of a firework’s fuel.
Potassium – Potassium helps to oxidize firework mixtures. Potassium nitrate, potassium chlorate, and potassium perchlorate are all important oxidizers.
Sodium – Sodium imparts a gold or yellow colour to fireworks, however, the colour may be so bright that it masks less intense colours.
Sulphur – Sulphur is a component of black powder. It is found in a firework’s propellant/fuel.
Strontium – Strontium salts impart a red colour to fireworks. Strontium compounds are also important for stabilizing fireworks mixtures. A combination of strontium salts and copper compounds gives purple colour.
Titanium – Titanium metal can be burned as powder or flakes to produce silver sparks.
Zinc – Zinc is used to create smoke effects for fireworks and other pyrotechnic devices.
Fireworks have been known for hundreds of years. But every year more research goes into making safer fireworks. In addition, some designers are using compressed air rather than gunpowder for safety. Also, the ingredients are being changed to make "green crackers" which more environmentally friendly, since some of the heavy metals used can be toxic to humans and animals and can pollute the air and water.
Next time you watch fireworks, remember that it requires an A to Z of chemical elements to give that marvellous coloured display!
Adapted from Science Made Fun!: https://sciencemadefun.net/blog/fireworks-and-their-colors and How Stuff Works: https://science.howstuffworks.com/innovation/everyday-innovations/fireworks.htm