How do fireworks create shapes?

The chemistry behind the spectacular patterns in the sky

Modern fireworks can burst into hearts, smiley faces and even a representation of the planet Saturn. The shape comes down to the construction of the firework’s shell (container) and the arrangement of the exploding stars (pyrotechnic pellets) within them. As aerial shells are often spherical, they tend to explode symmetrically. Arranging the stars into the desired shape on a piece of card within the shell makes them explode outwards in that pattern.

Manufacturers also use multi-break shells that have different compartments inside them, often with stars of various colours and compositions. When these are placed and fused in a specific order, they will explode in sequence to create recognisable patterns and shapes in the sky. However, it’s not an exact science; many displays will fire several copies of the same firework at the same time so that at least one of them creates the desired shape in the audience’s line of sight. 

Inside a firework
How does the design of a firework affect the shapes it makes in the sky? (click to zoom)

Sparkler science

The chemical composition of sparklers consists of three important components: an oxidiser, a binder and a metal fuel. These three substances are bound together in a paste, which is then coated onto the iron wire that forms the sparkler’s main body.

A powdered metal is essential, as it helps produce sparks that generate the famous glittery effect and can also colour the sparkler. Aluminium, titanium and magnesium all produce bright, white sparks, whereas iron will burn with a characteristic orange hue. When iron and titanium are combined they form an alloy called ferrotitanium, which produces golden yellow sparks when it burns.

For even more colours, salts of various metals can be added to sparklers, which is often the technique used for creating coloured fireworks. Copper salts produce green-blue, barium salts create green and strontium salts produce red.

Oooooooooohhh!…..Aaaaaaaahhhhh! via GIPHY

Happy 4th July, and cheers from across the pond! via GIPHY

 

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