Have you ever heard of a walking rainbow? Here is how you make one

For this experiment, we’ll be transporting water from one cup to another using only a paper towel. And to make it extra colorful, we’re going to be using food coloring to make it look like a rainbow! Let’s get started!

Here’s what you’ll need:

  • 7 clear cups (any size works but I’ll be using 9 oz. plastic cups)
  • Water to fill up 4 of the glasses (how much depends on the size of your cup, I’m using 1 cup of water for each of the 4 glasses)
  • Food coloring- red, yellow, and blue
  • 6 paper towels


Let’s get started!

Line up your 7 cups, rim-to-rim, then fill alternating cups with water. For example, you’ll fill the first cup with water, then the third cup, the fifth cup, and the seventh cup. Cups two, four, and six remain empty. Then, add several drops of red food coloring to the first and last cups.

Cup #3 gets yellow food coloring and cup #5 gets blue food coloring.

Before adding your paper towel, you may need to trim it. Ideally, the paper towel will reach from the bottom of one water-filled cup to the bottom of the empty cup, without extending too high above the rim of the glasses. Once you get the right length, fold the towel in half and put one end in the water cup and one end in the empty cup. Repeat all the way down the line.

Now, we wait! This part will likely take 30 minutes or more, be patient.


The experiment is complete with the water level in all the cups is the same. But wait--how did the water get into the empty cups?!?!?

It happened through a process called capillary action. It’s the same process trees and plants use to transport water from their root systems to the leaves. Like trees and plants, our paper towels are made of cellulose fibers. Water will travel through the gaps in those fibers to get from one cup to the next during our experiment.

You may notice the water crawling up the paper towel when you first dropped it into the cup. That’s capillary action...IN ACTION!

After the water levels in all the cups become equal, the process stabilizes and no more water transportation takes place. That’s also why the colors stop mixing. 

This is a great experiment for demonstrating the color wheel as well. We begin with the primary colors of red, yellow, and blue, and after everything mixes, we’ve created the secondary colors, or orange, green, and purple.

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