Why don't you try this rainbow science experiment at home.

Materials

• Paper Towel
• Washable Markers
• Water
• 2 Small Glasses

Method

1. Fold over a piece of paper towel (so you have 2 pieces on top of each other). Trim the length to be 7.5 inches (any longer and the rainbow may not connect fully).
2. Draw rectangles of the rainbow colours on each end.
3. Place 2 cups with water filled 3/4 full. You only want the bottom of the paper towel in so leave some space from the top of the cup.
4. The washable marker dye with slowly make it's way up with the water to meet the other side in the centre of the paper towel.
5. Leave the paper towel for 10-15 minutes and it will eventually connect the colours together.

https://www.youtube.com/watch?v=AoIkquEpD5Q