Source: How Fireworks Work | DNews
If your gonna blow your fingers of with fireworks you should at least know why it happens. Anthony here for D news. It’s the fourth of July which here in the US means we’ll be igniting various chemical explosive compounds in celebration of our freedom and also because fireworks a rad. But what’s actually in them and how can we control the explosions to look like specific shapes? Well the recipe for firecrackers has remained pretty consistent since their invention the 7th century. It’s basically just gun powder or flash powder wrapped in paper with a fuse. Chemically it perfectly shows off two of the main components all fireworks: a fuel and an oxidizer in this case charcoal and potassium nitrate. Potassium nitrate releases oxygen when heated that combines with the carbon in the charcoal. It also creates nitrogen gas. The expansion of the nitrogen and carbon dioxide puts pressure on the container and boom!
Sparklers also use potassium nitrate as an oxidizer and charcoal or sulfur as your fuel but those get dumped into water along with sugar or starch basically making a sort of chemical paste to put on the stick of the sparkler. Those are the binders that hold the paste together and in the final ingredient in our explosive soup is some sort of iron or steel or magnesium dust and those metal flakes get heated to the point of turning incandescent. That is where sparkler colors come from. That’s also why your mother was deathly afraid of giving you a sparkler because you are basically running around with hot metal shavings flying toward your tiny child eyeballs.
And now the good stuff: the rockets and the aerial shells that you see in huge displays. So these contain all the stuff we’ve seen before and then some. The container itself is called the shell and inside it’s filled with gunpowder and these little pea size spheres called stars. And each star is pretty much a sparkler. Now, traditionally, the shells get placed into a morter: a tube or a pipe with gunpowder at the bottom. You light the powder and that simultaneously lights the shell’s fuse and launches into the air. The fuse burns, hits a charge in the middle of the shell which ignites and then hits the Gunpowder, gunpowder ignites the stars and oooooh, aaaaahhhh.
Shells can have different compartments in them with different sorts of stars. Those are called multi-break shells and they allow for different colors and shapes throughout the launch so if you place shells in a specific layer in a specific shape they will create the same shape when they ignite and that’s how you get things like cubes and smiley faces and that stuff.