Walking Rainbow Experiment

1. Place 7 cups in a circle. Fill each cup with water about half an inch from the rim of the glass.

2. Add 10 drops of red food colouring to the 1st and 7th water glasses. Add 10 drops of blue food colouring to the 5th water glass. Add 10 drops of food colouring to the 3rd water glass.

3. Fold one sheet of paper towel lengthwise in half, and repeat this step again, leaving you with one long strip of folded paper towel. Cut this paper towel strip in half. You can also cut this paper towel strip into thirds if you would like the water to walk more quickly across each strip. Repeat this step for all sheets of paper towel, leaving you with 7 strips total. 

4. Place one strip of paper towel draping between the first water glass and the second water glass. Repeat this step, draping a piece of paper towel between each water glass in a clockwise direction for all water glasses. 

5. Observe how the water starts to “walk” across the paper towel strip almost immediately from one glass to the other. Be patient as you observe the colour creep from one water glass to the other. This may take up to an hour or more so feel free to walk away and come back to observe your experiment periodically.

WHY DOES THIS HAPPEN

The primary colour water is soaked up into the sheets of paper towel. As the primary colours continue to spread up to the end of the paper towel, the colour then “bleeds” into a non-coloured water glass. As the primary colours bleed into the non-coloured water glasses the colours begin to blend into secondary colours such as orange, green, and purple.