Food colouring fireworks in a glass

Last year, we went with friends to a fireworks display near to where they live in Yorkshire.  The small boy initially wasn't keen on the idea, but he enjoyed it in the end and saw that other children liked fireworks.  He was then actually quite keen on fireworks for a while.  However, this year, the fear has returned.  We'd hoped to take him to a low bangs display near home, but he won't even go near the window if he hears one.  It's a shame as he's spending quite a lot of time being scared of them at the moment with Diwali and Bonfire Night falling close together (27th October/5th November) and us being surrounded by other people who like fireworks.

I thought I'd try something that he might like, but which involved no bangs but some pretty colours, and see if I could entice him with 'silent fireworks in a glass'.  This didn't work, in more ways than one... I didn't make it work very well on the first attempt, so he didn't see why it was very exciting.  In fairness, it wasn't, but a subsequent attempt worked far better and his brother loved it.  Secondly, he realised it was in no way similar to actual fireworks, and thus it had no effect on his fear of the real thing.

So what did I do?  I mixed a few drops of different colour food colouring with a small amount of vegetable oil, and then dripped it onto the surface of a glass of water.  The idea is that the food colouring is suspended in the oil, but doesn't dissolve because it's not water-soluble.  When it's on the surface of the water (because the oil floats, just like in our previous experiment), when the food colouring moves within the oil and touches the water, there's a little burst of colour as it enters the water and spreads downwards into the glass.  As the little droplets of food colouring within the oil mix with the water at different times, there's a cascade of bursts of colour - a little like fireworks - over a period of a few minutes.

The first time I did it, I made two mistakes - firstly I mixed the oil and food colouring too much, so the droplets of food colouring were too small and the bursts of colour not big enough to have the 'wow' factor.  Secondly, I used too much food colouring, so each individual burst of colour wasn't very clear, and the water in the glass rapidly became so intensely coloured that you couldn't see further food colouring entering the water.  In hindsight, I should have tried it out before presenting it to the small boy; we'd usually try a new activity together unless it's likely to be fiddly (when I do try it out myself or with his brother as the audience first) but I wanted him to see this and then do it together as my main aim was to get him to be interested in something about fireworks without being scared.

Take two worked much better, but he didn't hang around long enough to see it!  I thought I'd try a third attempt a couple of days later, with the knowledge of how to make it work more effectively. I duly tried it when he was finishing a meal and was therefore a captive audience, but despite it working brilliantly (see video below), he was not at all impressed!

'Fireworks' of food colouring bursting out of the oil layer at the top of the glass

This idea was a definite failure, but I thought it was both pretty and scientifically interesting, so I'll try it again next year in the hope he might enjoy it more. Fingers crossed he's also more enthusiastic about real fireworks next year too...