Here is the link to the National Institute for Environmental Health (of America) where I got this idea;
It looked as though this might be a bit messy, but hey, I had fifteen minutes before it was time to leave for work, so I gave it a go. (If you haven’t clicked the link, this is what you do; pour some milk into a plate, add careful dollops of food colouring and then squirt in some washing-up liquid. It’s all to do with serious stuff about how pollution spreads across the earth if you want a context.)
OK, having tried it out, I would recommend that you do the same at home before you take it to the class. And on a Friday night, unless you are going to an important event over the weekend where you need to look your best. I’m not sure how long it will take for the red food colouring to wash off my fingers. Luckily I was wearing old jeans, and the smear of red (where I wiped my fingers) doesn’t matter too much. You should DEFINITELY cover all surfaces with paper first!
It is worth the effort; as the effect when you squirt in the washing-up liquid is quite spectacular.
For the composition, discuss how the different colours could be represented by instruments, and work out how to use the images as a graphic score to organise the way the instruments are played and combined. I guess if you don’t fancy creating your own food-colouring, milk and washing-up liquid pictures you could always use mine!