I cannot believe we haven't tried this before!! Have you?? It's easy, cheap and a lot of fun.
Late in the afternoon I realised we had milk in the refrigerator that expires soon. While thinking of ways to use up the milk I remembered this experiment.
Put milk in a tray (or bowl) and add a few drops of food colouring. Then to the tray of milk and food colouring add drops of dishwashing liquid. As the dishwashing liquid breaks down the fat and protein in the milk it makes lots of patterns and swirls. We put the dishwashing liquid in a bowl and used a pipette to drop it onto the tray.
As long as no one spills the food colouring it's a low mess activity. My boys poured in heaps too much food colouring but it still worked fine. It was a fantastic entertaining and educational activity for both my four and eight year old.
Let me know if you give it a go! I would like to try this with liquid water colours, I think it would work as equally well.