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Grow a Rainbow

Word of the Week

Capillary action (cap-ill-air-ee): The flow of a liquid into a narrow tube or porous material. The cool part is that gravity is not needed. It often works in opposition to gravity. The word

capillary comes from the Latin word capillaris, meaning "of or resembling hair."


Today I have a fun science project for you that shows capillary action at work. Let's dive right in!


  • Paper towel

  • Washable markers

  • Water

  • Two identical drinking glasses (it's fun if they're clear)

How it's done

  1. Fold the paper towel in half, horizontally.

  2. Cut off enough of the paper towel to create a strip that will fit inside your glasses.

  3. Draw rectangles of the rainbow colors on one end of your paper towel. Go over them a few times to really saturate the colors. Repeat on the other end of your paper towel in the same order so that matching colors are across from each other.

  4. Fill each glass about 3/4 of the way full of water.

  5. Carefully place one end of your paper towel into the first glass. Make sure only half of the part colored is submerged.

  6. Repeat with the other end of your paper towel, going into the second glass.

  7. Watch the magic as your colors travel to create a rainbow! This is capillary action at work!

Let's keep our science hats on a little longer and discuss things that might alter the outcome of this experiment!

  • The Paper Towel: Different brands have different patterns, different thickness, and different absorbency rates. How might this impact your growing rainbow?

  • The Markers: How new are your markers? Different brands may have different outcomes. How many times did you go over each color? The level of saturation will surely play a role.

  • The Water: Does using hot or cold water help speed up or slow down the process? You'll have to try the experiment twice to see!

Have some fun changing some of the variables. Who knew growing a rainbow could be so simple?!

Until next time. . .


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