How do fireworks and sparklers make shapes?

See how the internal design of the firework affects the shape of the explosion
See how the internal design of the firework affects the shape of the explosion

With an estimated 20 million people attending bonfire nights in November last year and London’s 11 minute New Year display costing £1.8 million, fireworks continue to be very popular and very expensive.

The success of a display relies on the expert construction of the firework shells and the precision with which the tiny pyrotechnic pellets are arranged inside them.

According to experts at How It Works magazine, the fireworks’ 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 then 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 the firework patterns you’ll recognise.

Meanwhile the chemical composition of a sparkler consists of three important components: an oxidier, a binder and a metal fuel. These 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: For example, Aluminium, titanium and magnesium all produce bright, white sparks; iron will burn with a characteristic orange hue and when iron and titanium are combined they form an alloy called ferrotitanium, which produces golden yellow sparks.

If you add copper salts it produces green-blue sparks, barium salts create green and strontium salts produce red.