How Fireworks Work
March 22, 2015
Last night an impromptu firework display occurred. I watched it from my bathroom window. Very pretty and somewhat extravagant, given that there’s no reason for one on the calendar. I could have filmed it on meerkat but it would have diminished the spectacle. However, it did at least motivate me to write this piece that I have put off for a while (since about November I guess?). One where I find out (i.e. look up on Wikipedia) how fireworks work.
Fireworks are essentially showy explosions, so the way they “work” from a practical point of view is the same as how gunpowder works. Light the fuse, and an exothermic reaction emits lots of energy in the form of light, heat, and a big bang.
The Chinese introduced the aesthetic element in the 7th Century (CE) and fireworks developed into a major part of Chinese culture. In Britain, fireworks have supplanted the more traditional burning of the Guy on “bonfire night”. It is likely that this transition occurred once China opened up to trade in the 1800s.
There are lots of ways to classify fireworks: ground-based versus aerial, noise-focussed (make as big a bang as possible) versus aesthetics focussed (ooh pretty), and so on. I suppose I should focus on aerial fireworks as they were the ones that I could see from my window. And they were pretty, so let’s look at why.
We can split prettiness further in to colours and patterns. For the aerial side of things, we will also consider how this can be used to make patterns.
When it comes to colours, it’s a matter of chemistry. You will no doubt be familiar with the bright white light emitted by burning magnesium, it’s one of the only experiments I remember from school chemistry lessons. (I also remember one with Bromine which really turned me off Chemistry. Achievement unlocked: make a joke about Bromine that no one will get.) Different metals glow different colours when they burn, so that’s basically that. It’s quite difficult to do precisely, which is why you tend to notice a “new” colour or why particular colours appear rarely. Last night I noticed a lot of magenta, so maybe that’s easier to produce now.
For patterns you have to think meta. You have a serious of explosions occurring at different times in different areas of space. You can control the time of ignition with the length of the fuse and you can control the trajectory of launch by orienting your sub-fireworks in a particular fashion around the bit that explodes. It’s quite an exciting problem in physics and optimisation to create particular patterns and time them together. Obviously sometimes you fire multiple rockets because that’s easier, you just time it so looks like that the second bursts of stars erupted from where the first ones died back.
In many ways, fireworks are a physical form of generative art. Now there’s something to think about - how could you apply the techniques of generative art to produce even better OMG firework displays? Competitive firework displays, now that’s something I could get into!