Wizard Science logoWizard Science
ExperimentsGamesSafetyAbout

← All experiments

Walking Water Rainbow

Ages 4+ with an adult10 minutes to set up, then a few hoursMess: Medium (food colouring can stain)
Grown-ups: please supervise this experiment the whole time. Read the safety notes first.

Watch coloured water climb up strips of kitchen roll and walk into empty cups, mixing new colours as it goes.

WOW FACT

Kitchen roll is made from tiny plant fibres. The same soaking-up action is why a towel dries you off.

🧰 What you'll need

6 clear cups or glassesSo you can see the colours.
✔ You probably have this
WaterStraight from the tap.
✔ You probably have this
Red, yellow and blue food colouringThe baking-cupboard kind works well.
✔ You probably have this
Kitchen rollOrdinary kitchen roll works best.
✔ You probably have this
A tray or old tea towelTo catch drips.
✔ You probably have this

✨ Want to go further? (optional)

Magnifying glass for kidsLook closely at the fibres in the kitchen roll.
View on Amazon (amazon.co.uk)
Plastic science beakersSee-through beakers show off the colours.
View on Amazon (amazon.co.uk)
Children's science experiment bookDozens of easy experiments for rainy days.
View on Amazon (amazon.co.uk)

💛 We may earn a small commission if you buy, at no extra cost to you. We only suggest things we'd use ourselves. How this works.

What to do

  1. Stand the 6 cups in a circle on the tray.
  2. Fill every other cup about three-quarters full with water, so full and empty cups take turns.
  3. Add red food colouring to one full cup, yellow to the next and blue to the last.
  4. Fold 6 strips of kitchen roll lengthways into long, thin strips.
  5. Put one end of a strip in each full cup and the other end in the empty cup next to it, so every cup is joined to its neighbours.
  6. Predict: what colour will each empty cup turn?
  7. Check after an hour, then again a few hours later.

What's going on?

Kitchen roll is full of tiny gaps between its fibres. Water is attracted to the fibres and to itself, so it creeps up into those gaps and along the strip. This is called capillary action. When it reaches the empty cup, it drips down and the cup slowly fills. Red and yellow make orange, yellow and blue make green, and blue and red make purple. The walking slows down as the water levels in the cups get closer.

Safety notes