Capillary Action Rainbow

Discover the magic of color mixing and capillary action with this easy and exciting science project!

Step-by-step tutorial

  • Learn moreMagnifying graphic

    Capillary action is a way of describing how water moves when it gets into tiny tubes or spaces, like in between hairs on your head or fibers in a piece of paper.

    Capillary action works because water molecules are sticky — not sticky like glue, but sticky enough to stay on your fingers after you wash your hands. Water likes to stick to itself, and it likes to stick to other things. When water gets into a tiny space like between paper fibers, it’ll stick to the sides of the fibers. Because it also sticks to other water molecules, more water gets pulled into the space after it. Gradually, by pulling in more water and sticking to the sides, the water will inch its way along and climb all the way across the paper!

    Check out capillary action at work in this wild, water-wicking experiment!

  • Step 1

    Gather your materials.

    Photo reference of how to complete step 1

  • Step 2

    Cut a few ½-inch wide strips from the center of a coffee filter. Then, cut each strip in half lengthwise.

    Photo reference of how to complete step 2

  • Step 3

    Place five cups about one inch apart from each other. Then, lay a small strip in between each of them.

    Photo reference of how to complete step 3

  • Step 4

    Squeeze two drops of red food coloring into the cup on the far left, two drops of yellow food coloring into the cup in the middle, and two drops of blue food coloring into the cup on the far right. Leave the other two cups empty!

    Photo reference of how to complete step 4

  • Step 5

    Pour water into each of the cups with food coloring, filling almost to the top.

    Photo reference of how to complete step 5
    Photo reference of how to complete step 5

  • Step 6

    What happened?

    Photo reference of how to complete step 6

  • Learn moreMagnifying graphic

    The water’s capillary action pulled it across the paper strips. It brought the food coloring too, and mixed it into beautiful new colors! 

    There are lots of other ways to experiment with capillary action and color. Did you know that capillary action is how water travels up the stem of a plant? The tubes inside of a stem work just like the fibers in the paper — better, in fact! Check out https://www.kiwico.com/diy/Science-Projects-for-Kids/3/project/Celery-Experiment/571, https://www.kiwico.com/diy/Arts-and-Crafts-Ideas/1/project/Carnations-plus-Food-Coloring-equals-Rainbow-Flowers/519, or search for other capillary action projects above.

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