Cool Coloured Milk

Cool Coloured Milk

Create an explosion of colour in a dish of milk!

Suitable for kids aged 3+ with parental supervision

You Need:
  • Milk
  • Dinner plate
  • Red, yellow, green and blue food colouring
  • Dishwashing liquid
  • Cotton swab
What to do:
  1. Pour enough milk onto a plate to cover the bottom. Allow the milk to settle.
  2. Squeeze one large drop of each food colour into the milk. Keep the drops close together, but not touching and mixing.
  3. Place a drop of dishwashing liquid on one end of a cotton swab.
  4. Touch the coated swab to the milk in the center of the plate. Be patient, hold the coated cotton swab still for about 10 seconds. Do not stir or move the swab or milk.
  5. Watch the explosion of colour in the milk as the food colouring swirls and mixes together. Add another drop of detergent to the cotton swab and place it in different sections of the milk. What happens? Do the colours continue to move when the cotton swab is removed? What makes the colour move and swirl?
  6. What happens when you touch a dry, uncoated swab to the milk? Try other types of milk like low fat? Do other liquids, liker water work? Why?

Why is it so?

Milk is mostly water, but also contains vitamins, minerals, proteins and tiny droplets of fat. Just like water, milk has surface tension. When detergent is added the cohesive bonds between the water molecules are broken and the milks surface tension is lowered, allowing the food colouring to move freely about in an explosion of colour.

The detergent also interacts with the protein in the milk, changing the shape of the protein molecules and the chemical bonds that hold them in solution. This sets the protein molecules in motion and as they bend, roll and twist they bump the food colouring molecules so we can see what would normally be an invisible party.

At the same time, the fat droplets are divided into smaller droplets and are surrounded by the detergent to form a micelle. This is what happens when detergent helps to lift grease off dirty dishes. As the micelles form, the pigments in the food colouring are pushed around. Eventually a steady state is reached and there is no more movement, but not till after youve enjoyed the show!