Easy Grow a Rainbow on Paper Towel Experiment

This colorful grow a rainbow experiment will amaze your kids! Learn how to grow a rainbow within minutes by using paper towels, markers, and two cups of water.

My daughter is currently obsessed with rainbows, so STEM rainbow activities are extremely exciting for her. Therefore, she was super happy to learn that we are going to grow a pretty rainbow on a piece of paper towel!

The best part about this walking water experiment is that it takes minutes to set up and uses very few materials. Young kids can do the entire experiment with little help from adults. Therefore, this simple yet magical activity is a perfect preschool or kindergarten science experiment to do at home or in a classroom.

Capillary action allows the colors from the markers to “walk” across the paper towel to form a rainbow right before your eyes. Prepare to wow your kids and for them to ask to do the experiment over and over again!

Let’s explore this amazing science phenomenon in this paper towel experiment!

How to Grow a Rainbow on Paper Towel

Materials:

• Paper towel
• Washable markers
• Water
• Two identical glasses

Directions:

1. Fold the paper towel in half horizontally.

2. Cut off about 1/3 of the paper towel. Save the smaller section for later.

3. Draw the rainbow colors on one end of the paper towel in rectangular blocks. Make sure to go over the colors a few times with the markers so there is enough dye to travel up the paper towel.

4. Repeat the same on the other end. Make sure the colors line up on both ends.

5. Pour water into the two glasses until they are about 3/4 full.

6. Place the two ends of the paper towels into the cups. 1/2 of the rainbow blocks should be in the water. Do not fully submerge the entire colored portion of the paper towel in the water.

7. Watch the colors travel up the paper towel! 

How long it takes for the color to travel up the paper towel will depend on how much dye you use and the absorbency of the paper towel.

We used Bounty, and the colors immediately climbed up the paper towel. However, it took about 5-10 more minutes until all the white space disappeared.

If you don’t cut the paper towel, it’s possible that the colors don’t travel all the way to meet in the middle. That would be a bummer to have a broken rainbow!

Paper towels are in short supply these days, so let’s not waste the ⅓ that you cut off. You can also color it with rainbow rectangular blocks just like you did with the other section, but just on one end.

Then dip the end of the paper towel in the water while holding it vertically and watch the colors climb upward!

Another thing we noticed was that the dye from the markers didn’t spread and dispersed right away in the water. The colors almost looked like the northern lights in the water – how pretty!

My kids immediately wanted to shake the water to mix the colors. I knew that after the colors mixed, they would just turn the water brown, so I told them to wait and enjoy the beautiful colors coming off the paper towel a little more.

Tips for the Grow a Rainbow Experiment

If your kids weren’t able to make a rainbow with their paper towels and markers the first attempt, here are some tips that might help:

• Make sure you use a nice, absorbent paper towel. I recommend the Bounty brand paper towels because they absorb the water quickly and allow the marker colors to walk across the paper towel. Using a less-absorbent paper towel may cause it to disintegrate before your rainbow has time to completely form.
• Use washable markers that are full of ink. The more washable the markers are, the better the colors will travel through the paper towel. I recommend the Crayola Ultra-Clean Washable Markers.
• When using markers, make sure you almost saturate the ends of the paper towel with the marker dye before putting the ends in water.
• Don’t use the entire piece of paper towel. If the length of the paper towel is too long, marker dye may not be able to travel across the full length and join in the middle before running out.
• Only put a portion of the paper towel’s ends in the water. If you submerge the section with the marker dye, the dye will simply dissolve into the water instead of walking across the paper towel.

Science Behind the Rainbow Paper Towel Project

Capillary action is what causes the water to move up the paper towel. 

Water adheres to the walls of the small vessels in the paper towel, causing an upward force on the liquid at the edge. In simpler terms, capillary action allows liquid to move through or along the surface of another material (the wall) in spite of other forces, such as gravity. 

Capillary action happens all around us and helps us with everyday life. For example, when you dry yourself with a towel after a shower, the towel absorbs the water from your body by using capillary action.

Plants and trees stay alive using capillary action. Water is absorbed by the roots, and capillary action allows the water to travel up the plant. I used this to explain to my kids why we should water plants at the base near the roots instead of sprinkling water on the leaves.

Check out how capillary action causes food coloring to travel up celery stalks and turn the leaves different colors in this fun color-changing celery experiment.

Final Thoughts on the Growing Rainbow on Paper Towel

Demonstrating capillary action with markers and paper towels is fun and very easy to do. It’s something to keep in your back pocket for days when your kids are driving you crazy, complaining they are bored. 

If your kids can’t get enough of this grow a rainbow paper towel experiment, make sure you check out the rainbow walking water experiment. The concept is very similar to this science project, where you watch the colors travel through the paper towel.

However, instead of growing a rainbow on one piece of paper towel, you will use multiple pieces to form a rainbow. Each paper towel will have its own color, created by the two different colors of water in each cup.

If you haven’t done it yet, I highly recommend doing the walking rainbow experiment as a follow-up to this one!

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