What better way to get kids excited about science than with an experiment straight out of a spy novel? Write a secret message using colorless ink, wait for it to dry, then use a special secret solution to reveal the message. This activity was inspired by the Berlin blue experiment in this chemistry kit. However, while that experiment uses strange-sounding chemicals and warns against putting the substances down the drain, I thought it would be fun to make something similar at home using common ingredients. I experimented a bit and came up with something that works well using only water, baking soda, turmeric, and rubbing alcohol.
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My kids and I have also done the lemon juice invisible ink experiment in the past. It works pretty well, but the one downside is that you really need to apply a lot of heat (like with an iron or hot plate) to get it to work. In my experience, holding the paper over a lightbulb just doesn’t cut it. That means I end up being the one to reveal the message while my kids stand by and watch. The nice thing about this color-changing invisible ink experiment is that no heat is required. Instead, it uses a homemade acid/base indicator to reveal the secret message.
I knew that I wanted to use a natural indicator (like red cabbage juice or turmeric) along with a basic solution. As you can see, I tried several different combinations before I found one that I was really happy with. It turns out a solution containing only baking soda and water really has a remarkable change in color when used with the turmeric/rubbing alcohol indicator. (See below for detailed instructions.)
The kids had such a great time making and reading secret messages. The best part…even the baby could reveal the message on his own since no irons or hotplates were involved. (Though I will warn you that if you’re worried about stains, maybe have them use paintbrushes instead of paper towels!)
Recommended Age Range: Preschool, Kindergarten, Elementary, Middle School, High School
Time Required: ~30 minutes (including about 15 minutes to let paper dry in the middle)
Cost: Under $10 (much, much less in used supplies). We had everything on hand, but turmeric can be a little expensive if you have to buy more than you will use. Maybe borrow a teaspoon from a friend!
- water (1/2 cup)
- baking soda (1 Tablespoon)
- q-tips (or a paintbrush) to apply invisible ink
- rubbing alcohol (1/2 cup)
- turmeric (1 teaspoon)
- paper towels (or a paintbrush) to apply color-changing solution
- measuring glass
- measuring spoons
- spoon for stirring
1. First, add 1 Tablespoon of baking soda to 1/2 cup of water.
2. Stir the baking soda into the water to make the “invisible ink”.
3. Use q-tips (or paintbrushes) to draw a picture with the invisible ink on paper.
4. While you are waiting for your paper to dry, mix up your color changing-solution. First, add 1 teaspoon of turmeric to 1/2 cup of rubbing alcohol.
5. Stir the turmeric into the rubbing alcohol. (Note: The solution can stain a little bit. I used a white plastic bowl, which was not the smartest, because it was a little difficult to clean afterwards. You might want to use a glass bowl.)
6. After the paper is dry, use a paper towel (or paintbrush) to apply the color-changing solution to the paper to reveal the secret message! (Note: We used paper towels, but our hands were all a little orange for a few hours afterward, so you might want to use a paintbrush instead!)
Enjoy reveling in the mysteries of science!
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