By Meredith Brustlin, CMNH Educator

We share a lot of different science experiment projects at CMNH. Many of these experiments have instant results - things like vinegar and baking soda bubbling, popcorn dancing, and invisible ink appearing. What I really like about this “walking rainbow” experiment is that it takes some time to see the results (as in, it takes hours to fully see the results!) Although it may not be as exciting in the moment, it is a perfect experiment to practice making predictions and thinking like a scientist. It really gives young scientists time to think and hypothesize and even change their guesses throughout the day. 

To make your own rainbow you will need:

• 7 clear cups--these can be glass or plastic, just make sure they are perfectly clear (not colorful)
• Water
• 6 paper towel pieces (this could be three large sheets cut in half, or 6 of the little half sheets)
• Primary colors of food coloring or liquid watercolor

Set-up:

1. Set out the 7 cups in a line
2. Fill cups 1, 3, 5, & 7 about halfway with water
   1. Leave cups 2, 4, & 6 empty
3. Fold your six paper towel pieces in half lengthwise and then in half again. Take that long skinny strip and fold it in half so that it can stand up in the cups (pictured above)
4. Invite young scientists to help you add some food coloring to the cups. 
   1. Ask them--what is the first color of the rainbow? Red! Add about 6 drops of red food coloring to the first cup.
   2. What is the second color? Orange! That cup is empty though, so we will skip that one. 
      1. Add yellow to the 3rd cup
      2. Skip the 4th cup (green)
      3. Add blue to the 5th cup
      4. Skip the 6th cup (purple)
      5. Add red to the 7th cup and ask your scientists why they think you may have done that…!
5. Next, carefully place your paper towel pieces in between each cup so that they are resting in the colorful water. 

That’s it for set up! Now it’s time to think like a scientist!

Ask your young scientists…

• What do you think will happen with the cups?
• Why do you think we left some cups empty?
• What do you know about primary colors?
  • How do you think what you know about primary colors (that they make secondary colors) will come into play in this experiment?
• What do you notice is already happening with the paper towel pieces and the water?

Feel free to have your scientists write or draw what they are seeing!

This experiment will take awhile to completely finish and make the rainbow design. It’s a good idea to either do this experiment at night before bedtime, make some predictions, and then wake up and see the walking water rainbow. You could also do this experiment first thing in the morning and then watch it change all day long!

Have fun making a walking rainbow and thinking like scientists!