Fireworks. They have been a source of happiness of children for many ages now. But where do they actually come from? What are the mechanics of the aerial displays? What is the secret of fireworks?
Fireworks are classified as low explosive pyrotechnic devices. In simple terms, it means that they have a large enough energy potential for people to be able to see as they explode. Fireworks produce a variety of effects, ranging from visual (smoke and flashy lights) and auditory (boom noise), to physical (discarded materials) and olfactory (smell of fumes). The origin of these effects will be explained later.
Figure 1
Source: Tokyo Fireworks and Restaurants: A Sumptuous Summer Guide, Savor Japan.
But first some history
Invented in the 10th century, gunpowder revolutionized China. The formula for the explosive, so simple yet so useful, thoroughly changed the world. Also, it was gunpowder that made fireworks possible.
First fireworks came from Song Dynasty China (9th-12th century AD), when the Chinese used them in all kinds of celebrations, be it Chinese New Year, Coronations, or other holidays. As fireworks’ popularity grew, even ordinary people were able to afford them.
So did the 11th century Chinese have beautiful, coloured airshows? No, as coloured fireworks were invented in 14th century. In this very same 14th century fireworks were first seen in Europe. But it wouldn’t be until 17th century when they became popular.
Here it is important to note that China is still the leading producer of fireworks: the pioneer has never in history lost this position. It is also considered to be the best at producing aerial display fireworks.
What are aerial fireworks?
Aerial fireworks are the most popular variety of fireworks. They are the colourful ones that burst into colourful stars when shot up into the air. They comprise four chemical components – fuel, colorant, binder and oxidizer. Gunpowder serves two purposes, both as fuel and as an oxidizer. The function of a colorant is most commonly served by metal salts.
But how do they work?
The explosion of a gunpowder-filled propulsor on the ground sets a delayed ignition on the packet of confetti stars and shoots it up high into the air. While in the air, the flame reaches the packet and stars scatter around. This is due to rapid combustion of fuel supported by oxygen rich compounds. This combustion creates a huge, extremely hot, and thus rapidly expanding gas bubble that pushes the stars in all directions. This is how the stars are scattered, but where does the colour come from?
Unfortunately, the answer to this question is much more complicated
Figure 2
Electromagnetic Spectrum.
Source: “Light and photosynthetic pigments”, Khan Academy
Colour of fireworks
First, we need to understand what the colour we see is. It is simply light of different energies that our eyes can perceive as depicted in Figure 2. Energy of a light wave is proportional to its frequence. The more frequent a wave, the shorter its wavelength and the higher its energy. Now, every colour has its own, unique energy and wavelength. In the visible light spectrum, colour red, for example, has a wavelength of about 680 nm.
Since we’ve learnt what colours are, let’s ask ourselves one more questions: how comes fireworks come in different colours? Well, it is due to the abovementioned colorant. Different colorants are made from different atoms, which have different properties.
One of these properties is the distance between the atom’s nucleus and its regions of high electron density (energy level). The further an energy level is from nucleus, the higher its energy. Light is produced by these atoms when an electron moves from a higher energy end (one far away from nucleus) to a less energetic one (one closer to the nucleus). When an electron moves from high to low energy, something has to happen to the remaining energy from the high energy level: it is released to the environment. We call this process emission, as it emits (throws out) energy. Each atom has its own very specific emission spectrum, and thus it produces a different colour of light.
Light is a direct product of emission as it is simply energy. Energy emitted by atoms causes them to light up in a certain way.
But why do we need energy (heat from the fuse) to light up our fireworks?
It is due to how emission is obtained. In order for emission to occur, first a process of absorption needs to happen. Absorption is a process of an atom taking in energy to move its electron(s) to a further energy level, for example, from first closest to the nucleus, to the second closest. After that, the electron needs to go back to its prescribed energy level. This is when emission occurs, and lights of different colours appear.
Figure 3
A Diagrammatic Representation of Absorption and Emission.
Source: “Atoms and Light”, Harper College
So now you, dear reader, know how fireworks, which bring us so much joy, actually work, and what the chemical mechanism behind them is.
Bibliography:
Fireworks. Public Domain via Wikimedia Commons.
History of gunpowder. Public Domain via Wikimedia Commons.
Firework. Public Domain via Encyclopedia Brittanica.
Fireworks: What Do We Know About Fireworks?. Public Domain via ACS Chemistry for Life.
Formation of ozone by fireworks . Attri A., Kumar U. & Jain, V. Nature 411, 2001.
Tokyo Fireworks and Restaurants: A Sumptuous Summer Guide. Savor Japan.
Light and photosynthetic pigments. Public Domain via Khan Academy.
Atoms and Light. Public Domain via Harper College.