Let’s take a journey to 12th century China, where mixtures of sulfur, charcoal, and potassium nitrate (what we now call “gunpowder”) were first crafted in “laboratories”. This mixture was used to create the first fireworks, which were used for both military and ceremonial purposes.
This technology made its way to Europe and by the 1800s, chemists began adding compounds to the gunpowder to create an array of colors. Many of which were quite toxic! (Think: mercury, arsenic, and barium.)
This shift of gunpowder components moved the chemistry away from “black body radiation” aka burning things to make them glow from the heat of burning and instead to burning materials so that their gas-phases excitations emitted strong colors!
More on the history and evolution of fireworks here and here.
Present day fireworks all have the same basic premise, a two-step explosive physics masterpiece. First, the “aerial shell” is placed in a tube (or “mortar”) with gunpowder. The gunpowder is lit and the aerial shell is launched into the air. Then, there is a second timed fuse on the aerial shell that ignites the secondary capsule of gunpowder and other metals, causing the colorful explosions were know as “fireworks”.
Fun fact: the boom that you hear when fireworks go off occur because the gas explodes and expands faster than the speed of sound. That boom? It’s a sonic boom.
Need more science? Check out this overview.
Let’s be real. This is the coolest part. Check out the infographic below to see which metals/compounds you need to mix to get your desired explosive color palette.
If you’d like to know even more about fireworks, and maybe even do some at home experiments, check out the American Chemical Society’s deep dive into the world of fireworks.
And have a happy and safe Independence Day!
