For many of us, the fireworks finale of the annual National Day Parade is the highlight of our Nation’s birthday bash. Comfort-loving citizens turn into crazy campers every 9th of August, ‘chope-ing’ space and braving the heat on the unsheltered waterfront hours in advance. These are just some sacrifices that we Singaporeans make to get a good view of what often feels like a ‘not-long-enough’ firework display.
Well, that fondly amusing sight won’t be happening this year, now that the much-anticipated fireworks show has been cancelled, no thanks to Covid-19. With nothing to marvel at by the waterfront this National Day, why not dive deeper and learn about the chemistry of fireworks?
A firework involves a chain of combustion reactions that kick starts once it is loaded and lit. But there are many different types of fuel and sources of oxygen available, creating a plethora of possible fuel-oxidizer combinations. This is better known as black powder or gunpowder. Sulphur, charcoal, magnesium and aluminium powder are popular choices for fuel; they determine the heat output and burning rate of a firework. Then, you have oxidisers that supply different volumes of oxygen at different rates to sustain combustion. Common oxidizers include potassium nitrate, potassium perchlorate, and strontium nitrate. The type of fuel and oxidizer used in a firework has to be taken into careful consideration for different spectacular displays.
All this might sound exciting, but the real fun begins with the addition of colour producers. According to John A. Conkling, author of the book “The Chemistry of Pyrotechnics: Basic Principles and Theory”, when different chemical elements are heated to high temperatures, they try to get rid of energy by emitting different wavelengths of light. For example, burning barium salts would give off a nice green colour, while copper salts burn blue. A more extensive list of various elements and the colour produced by their burning salts is shown below. The addition and combination of different metals or chemical salts would therefore determine the colour of a firework.
As with every other recipe, you often need a bowl or container of some sorts to mix all your ingredients together. In the case of a firework, fuel, oxidizer, and colour producers are assembled in a cardboard holder known as an aerial shell. The fuel-oxidizer combination or black powder goes into the propellent and bursting charge compartments, while chemical salts go into the effect pellets.
The aerial shell is then loaded into a mortar tube. When the main fuse is lit, it will ignite the propellant charge and launch the aerial shell into the sky.
The time-delay fuse, which is now ignited from the burning propellent charge, burns for around 3-5s, eventually igniting the bursting charge, causing it to explode through the shell. This motion allows the black powder to pick up chemicals in the effect pellets, burning a certain colour until combustion fizzles out.
And there you have it – the features of a firework! Although it is easily deconstructed for simple explanation, there is a lot of complicated prototyping and experimenting of new chemical mixtures, different black powder amounts, varying fuse lengths, among other factors in hopes of building bigger and better fireworks. But of course, this is best left to the professionals.
Us layman firework-enthusiasts should just sit back, relax, and marvel at the next possible fireworks show. Just remember that you can’t have beautiful explosions lighting up the night sky without some precise calculations and a complex concoction of chemicals.
Written by Genevieve Teo
Illustrations by Lim Daphne