

Magic Milk
Use soap to produce swirling colourful patterns of food colouring dissolved in milk.
This activity may be Messy and Stimulating
Use soap to produce swirling colourful patterns of food colouring dissolved in milk.
This activity may be Messy and Stimulating
What will I need?





- What happens if you use different types of milk, such as semi-skimmed, low fat or soya milk?
- What happens if you use water instead of milk? Will it still work?
- Try different types of soap and see which one works best.
- What colours do you think you will see when the different food colourings mix?
- What is making the food colouring move?
Food colouring dissolves well in pure water. Milk is mostly water, but it has billions of tiny droplets of fat suspended in it. Food colouring doesn’t dissolve in fat, so the droplets prevent the food colouring from mixing very far into the water.
The water molecules at the surface of the milk are all pulling on each other, so the surface is under tension. Washing-up liquid reduces the surface tension, but only where the drop falls. Like the rubber of a burst balloon, the rest of the surface rapidly pulls away, and this causes the milk to churn and mix, resulting in the colours you see.
You can’t blow bubbles in pure water, because water’s strong surface tension pulls it into round droplets.
Dissolving soap in water reduces the surface tension, making it possible to blow bubbles.
