Colour Changing Milk

This is one of our favourite science chemistry experiments so far. Some very unusual interactions took place when we mixed a little milk, food colouring, and a drop of washing up liquid.  We created an awesome reaction and a beautiful explosion of colours.

What we did:

1. We poured enough milk into a dinner plate to completely cover the bottom to the depth of about ¹/₄ inch. We allowed the milk to settle before moving on to the next step.
2. We added one drop of each of the food colours—green and blue—to the milk. We kept the drops close together in the centre of the plate of milk.
3. We then placed a drop of washing up liquid soap on one end of the cotton bud. We placed the soapy end of the cotton bud in the middle of the milk and held it there for 10 to 15 seconds. We observed the burst of colour!

How did this happen?

The molecules of fat in the bend, roll and twist in all directions as the washing up liquid molecules race around to join up with the fat molecules. During all of this fat molecule gymnastics, the food colouring molecules are bumped and shoved everywhere, providing an easy way to observe all the invisible activity.