This activity is for kids 2.5 and up!

Get ready for an incredibly simple set up with an incredibly entertaining result. You won’t believe how easy it is to make your own color changing paint with just two ingredients: red cabbage and white paint (and honestly, you can leave out the white paint and it still works, just more like water colors). Red cabbage has a huge amount of the highly pigmented group of molecules called anthocyanins. Widely known for their antioxidant capacity, these molecules also have the amazing ability to change color when exposed to a pH change. Read on for the method to make your own color changing paint and a little science lesson below!

Materials

• • red cabbage
  • white paint (we used this tempera paint Handy Art Little Masters Tempera Paint 16 ounce, White, but any will probably work!) (optional!)
  • blender, food processor, juicer, or pot with hot water
  • strainer/ paper towel/ cheese cloth
  • paper and paint brush

For the Painting Activity:

• paint brushes
• a selection of safe household acids and bases (lemon, vinegar, baking soda, apple juice)
• eye protection (because even though lemon juice and the like are safe, it still hurts if you get it in your eyes)

Procedure

1. Chop up a cup or so of red cabbage and place in your blender, food processor or juicer. (If you’re using the former two, you will have to add a little water to it). Blend until it’s a pulp. If you don’t have any of those, you can boil some chopped cabbage in water use the cooled liquid.
2. Strain and press the purple liquid from the cabbage pulp.
3. Pour out some white paint into a container then add a little cabbage juice until it is a nice pastel color. About 2 tbsp paint to 1-2 tsp cabbage juice worked for us, but will depend on how concentrated your juice is. Our new paint turned from purple to blue (it just means the paint is a little basic). Alternately, you can skip the white paint and use the straight cabbage juice. You will get more vibrant colors with this, but it’s a little more messy.
4. Paint a whole sheet of paper with your cabbage paint and let dry
5. Set out your selection of safe acids and bases (don your eye protection)
6. Starting ‘painting’ on your color changing cabbage paint!
7. Note what colors appear and try to group your household products into acids and bases based on the color changes (see below for help).

Above are pictures of the cabbage juice mixed into tempera paint. This is a lot less messy than using straight cabbage juice, but not as vibrant. Since our paint turned blue (and was already a little basic), baking soda did not really change the color much, so we stuck to lemon juice and vinegar.

Here is painting using straight up cabbage juice with lemon juice and baking soda solution (2 tsp soda to 1/4 cup warm water). This stains! FYI 🙂

Discussion

The molecule responsible for the purple color of red cabbage is anthocyanin. Anthocyanins are also present in many other plant products like red wine, blueberries, and red autumn leaves. There are many different specific anthocyanins but they all share a common core structure. When you introduce an acid or base to an anthocyanin, a reaction occurs where you are slightly changing the molecule by taking or giving a “proton,” also known as a hydrogen ion. (Remember that acids can give protons and bases take protons). Many molecules can donate or accept protons, but some molecules, like anthocyanin, change color when this occurs. We call these indicators because they “indicate” or let us know a pH change is occurring by changing color. (You might remember this from high school or college chemistry when you were titrating a base with clear/pink phenolphthalein as the indicator). Anthocyanins are incredibly amazing indicators in that they can take on a wide range of colors depending on the pH because they have several sites on the molecule that will cause a color change when a proton is present or missing. Here is an info graphic from the amazing site Compound Interest (www.compoundchem.com). Source

When working with kid-safe solutions, you’re really only going to be able to access the middle range of pH/colors. Lemon juice (pH 2-3), vinegar (pH 2-4), apple juice (pH 4-5) or cream of tartar solutions (ph 5) will get you some nice shades of pink, while baking soda solution (~pH 8-9) will get you blues and greens. You can even try your tap water- ours is alkaline at pH 9, so that yielded a pretty teal color. Depending on how old/responsible your children are, you can give them one to several acids and bases to paint with. Even though these are relatively safe, always have your child wear eye protection. And let them know that they should not be eating any of this even though it’s food. My daughter struggled with this and tried to convince me that she could eat it. I just told her (3 years old) that even though all the things we were using are edible, we shouldn’t be getting into the habit of eating our art/science projects because often they are not edible.

Have a great time trying this out! Send me your artwork to be featured on Instagram @TheBabyBiochemist or on Twitter @BabyBiochemist!

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