pH Rainbow Tube

How to make an easy pH rainbow tube or rainbow wand

Cabbage juice displays a rainbow effect when you drip common household acids and bases into it.
Anne Helmenstine

Make a rainbow in a glass or tube using common household ingredients. The rainbow effect is caused by using a colorful pH indicator in a liquid with a pH gradient. You can keep changing the colors by adding chemicals to alter the acidity or pH of the liquid. Here's what you need:

pH Rainbow Tube Materials

  • red cabbage
  • hot water
  • paper towel or coffee filter
  • glass or tube
  • one or more acids: lemon juice, apple juice, carbonated soda, wine, vinegar
  • one or more bases: ammonia, baking soda, soap, detergent

Prepare the Red Cabbage pH Indicator

Red cabbage pH indicator solution is useful for several projects. You can refrigerate leftover solution for several days or freeze it for months.

  1. Coarsely chop the cabbage.
  2. Place the cabbage in a food processor or blender.
  3. Add very hot or boiling water. The amount is not critical.
  4. Blend the mixture. If you don't have a blender or food processor, soak the cabbage in hot water for several minutes.
  5. Use a coffee filter or paper towel to strain the liquid, which is your pH indicator solution.
  6. If the liquid is very dark, add more water (any temperature) to dilute the liquid to a paler color. If the water you used to prepare the cabbage was neutral (pH ~ 7) then this liquid will be purple.

Make the pH Rainbow Tube

The actual rainbow tube is easy to assemble.

  1. Pour the cabbage pH indicator solution into a tube or glass.
  2. To get a rainbow effect, you want a pH gradient so the liquid is acidic at one end of the tube and basic at the other end of the tube. If you want to be exact, you can use a straw or syringe to deliver an acid to the bottom of the tube. All you need are a couple of drops of an acid, such as lemon juice or vinegar.
  3. Sprinkle a couple of drops of a base, such as ammonia, on the top of the tube. You'll see the rainbow effect develop.
  4. A simpler method, which has worked well for me, is simply to drip an acidic chemical on the tube, followed by a basic chemical (or the other way around... doesn't seem to matter). One of the chemicals will be heavier than the other and will naturally sink.
  5. You can keep adding acidic and basic chemicals to play with the color of the solution.

Watch a YouTube video of this project.

Gelatin pH Rainbow

We used a glass for the example in the photo, but you can find plastic tubes at many stores. An interesting variation of this project is to use boiling hot cabbage juice to make plain gelatin. This works the same way, except the color develops more slowly and the rainbow lasts much longer.

Storing the pH Indicator Solution

You can keep leftover cabbage juice in the refrigerator for several days or you can freeze it for months. The rainbow tube lasts for a day or two on the counter. If you leave it out, you can watch the colors slowly bleed together until the liquid assumes a fixed pH.

Rainbow Tube Clean-Up

At the end of the project, all of your materials may be washed down the sink. The red cabbage juice will stain counters and other surfaces. If you spill any of the indicator solutions, you can clean up the stain with any kitchen cleaner that contains bleach.

More Rainbow Projects