How can I make fireworks different colours?

07 January 2014

Question

We made gunpowder at our sixth form using the standard recipe with potassium , charcoal and sulphur. We wanted to try and change the colour of the flame by using different metal salts, strontium, copper and magnesium nitrates, but these didn't burn. I was wondering if you could suggest why using the different salts in the same ratio didn't work as gunpowder, and how could we produce coloured flames in gunpowder? Thanks you!

Answer

Mark - I suspect it's because if you're detonating gunpowder, the reaction is simply too quick. Everything is going to be blown apart before you actually get a chance to excite those metal atoms and start them emitting the colour of light that you want. Fireworks are constructed in a very particular way to actually make those metals burn. It's a slightly slower burn as the fireworks go off. That's why when you see fireworks go off, you've got strontium in there and that's making this intense red, barium for green, and so on.

Dave Ansell - The other effect is that if you've got lots and lots of carbon in there, carbon tends to glow. If it hasn't actually burned completely and really combustive carbon glows bright yellow. So, if you're not careful, that's going to completely overwhelm your nice colours in the fireworks as well.

Mark - Did she say what colours she got in the explosions?

Chris - No. She just said it didn't work very well.

Mark - Well, that is a shame.

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