The Chemistry of Fireworks

I love fireworks!  I could watch a firework show for hours, so any opportunity I get here in Australia to see them I do.  I also love chemistry, my favourite topic is the modern atomic theory, and the reactions between complex mixtures of chemicals and the outcomes. What made me think of this was actually the film The Lord Of The Rings that was on last night,  where Gandalf throws a spectacular firework display on the eve of Bilbo Bagging's fair well.  I started to think about the complex chemistry that is going on to make such beautiful aesthetic entertainment that most people don't even think about.
So this prompted me to write a short blog on the chemistry of how fireworks, work!

I guess the art of using mixtures of chemicals to produce explosives is an ancient one to say the least.  Black powder - a mixture of potasium nitrate, charcoal, and sulfur - was being used in China well before 1000A.D. and is also used in military explosives too, no surprise there, also in constuction blasting and, of course, fireworks.  Years and years ago fireworks just used to be basically rockets and loud bangs and the colours such as orange and yellow came from charcoal and iron fillings.
However, great advances in chemistry in the 19th century had new compounds finding their way into fireworks.  Salts of copper, strontium, and barium added some brilliant colours.  Magnesium and aluminium metals gave a dazzling white light. 

So, how do these fireworks actually produce these brilliant colours and rather loud bangs?  There is really only a handful of different chemicals that are actually responsible for the most spectacular effects.  To produce the noise and flashes, an oxidizer, (something that has a strong affinity for electrons) is reacted with a metal such as magnesium or aluminium mixed with sulfur.  The resulting reaction produces a brilliant flash, whixh is due to the magnesium and aluminium burning, and a loud bang is produced by the rapidly expanding gases.... cool huh?

For a colour effect, an element with a coloured flame is included.
Yellow colours in fireworks are due to sodium, strontium salts give the red colour and barium salts give the green colour.  Achieving the vivid white flashes and the brilliant colours requires complex combinations of chemicals.  For example, because a white flash produces high flame temperatures, the colours tend to wash out.  Another problem arises from the use of sodium salts.  Because sodium produces an extremely bright yellow colour, sodium salts cannot be used when other colours are desired, ( It would be worth checking out the energy states of atoms that goes into more detail about the colours that elements give off during different energy levels).

In short, the manufacturer of fireworks that produce the desired effects and are also safe to handle requires very careful selection of chemicals.  No wonder they cost so much!