Rainbow Test Tube

Grow colorful crystals that mix colors until you have a complete rainbow!

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Grow and color jelly-like crystals, then layer them in a plastic tube so you can see the colors blend and change. Our baby soda bottle “test tube” makes it easy to see the scientific results, and it's small enough to carry your “rainbow” wherever you go! Included is a science activity guide to teach you all about crystals and color!

Here's What You'll Need

  • Baby Soda Bottle
  • Water Jelly Crystals (blue, red, and yellow)
  • Three cups or containers
  • Water


  1. Collect some red, blue, and yellow Water Jelly Crystals. Put each color on a separate paper towel to absorb any extra liquid. Find the Baby Soda Bottle cap and the now empty Baby Soda Bottle.
  2. Now it’s time for your resident scientists to choose a color. Pick red, for example. Scoop red crystals into the Baby Soda Bottle until it’s one-third full. Then, fill the next third with blue crystals. Finally, top it off with yellow crystals. Make sure the yellow crystals are overflowing out of the tube before you squish them down with the soda bottle cap.
  3. If you wait a few minutes, you’ll notice that the red begins to mix with the blue and the blue with the yellow. This is a great time to show your assistants how primary colors (red, yellow, blue) mix together to form secondary colors (orange, purple, green).
  4. If you want, you can wait a few days and check out the Rainbow Tube again. Have your young scientists color the blended crystals on the back of the card. Save the extra Water Jelly Crystals for a later activity.

How Does It Work?

When you first look at the Rainbow Tube, the color mixing is caused by light passing first through one color and then through the other. After a day or two (if you’ve really stuffed the tube), you’ll see both the purple and green bands getting wider. The colored water in the blue crystals mixes with the colored water in the yellow crystals and makes green colored water. The gel takes the new color and you have a green crystal.  Science is so cool!

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