Test Tube Rainbows – Splitting Colour Experiment

Test Tube Rainbows – Splitting Colour Experiment

We’ve had great fun with this experiment today, and it’s super simple to do. If you have any test tubes to use they are ideal, but you could use any glass container that you have to hand. Appealing to children of all ages, the great thing with this experiment is they can all get involved and take from it what is relevant to them.


  • 7 test tubes (or glass receptacle)
  • Red, yellow and blue colours (we used cosmetic colourant, but food colour would work just as well)
  • Pipettes


  1. Fill all of the test tubes around half full with water.
  2. Add the blue, red and yellow colour to three of the test tubes.
  3. Line the test tubes up with the three colours going into their correct places in the rainbow colour sequence.
  4. Using the pipettes, take colours from the primary colour tubes and make up the missing colours.


We managed to make the rainbow from our 3 primary colours! The experiment is good fun in itself, but it’s also good as a place to start further investigation. We’ve been trying to make rainbows with a prism and seeing how close our colours match. If you’ve any further rainbow ideas to add, be sure to share them with us!

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