Sodium nitrate, sulphur and carbon. Mixed together make gun powder. That is the explosive mixture they put into fireworks. The ratios of the different elements determine the burning characteristics. Strontium makes red, sodium yellow, copper green, magnesium bright white, other elements make different colours. Cobalt? Possibly blue. The elements burn at different temperatures. Each element, when heated, excites electrons in its atoms. As they cool down again photons of light are given out (emitted). The colour depends on the energy the photons release. Bear with me it gets complicated! In the same way you can tell what elements are in the sun or other celestial objects by their emission lines. If you look at a spectrum (rainbow of colours), given out by the light of the sun there are gaps, these correspond to gases like Hydrogen and Helium.

I don’t know enough science to explain properly.

Anyway the fireworks have stopped so I might go to bed.

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