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.
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 your 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 paint brushes 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
- First, add 1 Tablespoon of baking soda to 1/2 cup of water.
- Stir the baking soda into the water to make the “invisible ink”.
- Use q-tips (or paintbrushes) to draw a picture with the invisible ink on paper.
- 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.
- 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.)
- 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 afterwards, so you might want to use a paintbrush instead!)
Enjoy reveling in the mysteries of science!
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