Wednesday, July 1st 2020, 12:00 pm - What makes one firework red, and another green?
Canada Day and the Fourth of July 2020 are happening this week! So, we can expect to see a lot of fireworks going off across both countries, from small backyard displays for the family to big virtual shows streaming on the web. So how do these delightful displays actually happen?
While fireworks come in many shapes, styles and sizes, there are two basic types - the sparkler and the firecracker.
Remember waiting for the fireworks to begin, filling the time by running around, waving a sparkler through the air? Possibly, while making your parents worried about you potentially hurting yourself or setting something on fire? Well, you may not have realized it, but you were holding in your hand one of the essential components of the colourful displays you were waiting for.
A sparkler. Credit: Getty Images
A sparkler's characteristic sparks come from a mixture of chemicals and powders. Metal powder, sometimes combined with charcoal and sulphur, acts as a fuel source, and the metal provides the coloured sparks. Something like potassium nitrate, or barium nitrate, or strontium nitrate is used as an 'oxidizer', which provides more oxygen to the flame and causes the sparks to fly off in random directions. The whole mixture is held together and stuck to the thin metal handle by a binder, such as dextrin. Even though sparklers don't explode, anyone holding one (especially children) should be very careful with them. They burn at temperatures of at least 1,000°C, which is more than enough to cause severe burns or even ignite clothing. Be especially mindful of where the sparks land if there has been dry weather in your area.
The firecracker is much simpler. Gunpowder is packed into a paper tube or sphere, and the tube or sphere is sealed tight, with a fuze to deliver a flame to the interior. These are designed only to explode, delivering a loud bang, with the only flash of light coming from the explosion itself. The size of the firecracker, and thus the amount of gunpowder contained within it, determines how big of an explosion is produced.
While firecrackers are banned in many places, we still see them here in one form or another. This is because firecrackers are combined in different ways with sparklers to make firework shells, which are the basis for all firework displays, with the big booms, and the huge, colourful blossoms of light, high in the sky.
The most basic firework shell is an empty cylinder or sphere made of paper and string. At its core is a firecracker, called the burst charge, which is linked to the outside of the shell by a timing fuse. Gunpowder fills the remaining space inside, with small stars made of sparkler mixtures embedded into the gunpowder.
Some firework shells can be MUCH more complex, like this roughly metre-wide Japanese shell, which features not only sparkler spheres lining the interior, but also nested shells that contain even more sparkler spheres, designed to go off well after the initial burst. Credit: Joel(frikitiki)/Flickr
After the fuse is lit, the shell is launched into the air (using a special launch tube, or a launch charge incorporated right into the shell). The timing fuse is slow-burning compared to the rest of the components of the firework, so that the shell can reach high enough for the display it produces to be visible for kilometres around when it goes off. When the burst charge finally explodes, it ignites the gunpowder, which simultaneously sets the stars burning and causes the shell to blow apart, throwing the burning sparkler spheres outwards in all directions.
A multi-colour firework burst. Credit: Epic Fireworks/Flickr
Fireworks come in a variety of colours, as well. These colours are achieved by using very specific metals or chemicals in the sparkler stars. Some of the most common are listed below:
- White - aluminum or magnesium
- Silver - aluminum, magnesium or titanium powder
- Blue - copper chloride or copper compounds
- Red - strontium salts or lithium salts
- Green - barium chloride
- Yellow - sodium nitrate
- Orange - calcium chloride
- Purple - mixing strontium and copper compounds
Multiple stars of different types can also be packed into the same shell, producing a spectacular multi-hued display when it explodes.
If the sparkler stars are packed into a shell randomly, this results in a spherical display known as a peony, named after the flower. Firework designers can cleverly shape the displays to their wishes, though, by changing up the sparkler mixtures and carefully placing the stars in specific patterns. This is how we get displays called dahlia and chrysanthemum, that resemble other flowers and the tree-like palm and willow. They can also make rings, stars, spiders, waterfalls, and a host of other shapes as well.
Even further, special effects can be achieved by organizing different layers of gunpowder and stars that go off at different times. One way of accomplishing this is by packing a larger shell with several smaller shells. Another way is to change the composition of the stars so that they burn longer, crackle and whistle as they burn, or burn down and then expose a core that explodes.
The crossette display, where trailing stars shoot outward, then each suddenly splits apart into its own burst of trailing stars, is an excellent example.
A crossette display. Credit: Epic Fireworks/Flickr
And the really great thing is that this knowledge of the science that goes into making these fantastic displays takes nothing away from the awe they inspire.