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Invisible Ink

Invisible Ink

August 31, 2023

Have you ever wanted a way to write a secret message to a friend? Today, we are going to do just that! During the Revolutionary War, spies for George Washington used lemon juice based ink to send messages that were hidden in plain sight. Today we will be testing out two different invisible inks!


- Small Bowl or Cup

- Paper

- Cotton Swab or Paintbrush

- Lemon Juice or Lemon Powder

- Baking Soda

- Hair Dryer


1. Pour some lemon juice into the bowl. Then add a little water so it is not as concentrated. Lemon powder works too.

2. Dip your cotton swab in the solution and write a message on a sheet of paper.

3. Allow the ink to dry so that the message becomes entirely invisible. This may take a few minutes.

4. While waiting for the first message to dry, repeat the steps above with equal amounts of baking soda and water.

5. Once both messages have dried, take a look at them. Can you see or read them?

6. Use the hair dryer to blow hot air onto the messages. What do you see happen?

What’s happening? This type of invisible ink appears when heat is added. The lemon juice and baking soda both contain carbon compounds that begin to break down when heat is added. When the carbon compounds are exposed to oxygen, they go through a process called oxidation and turn brown, allowing the juice, and message, to become visible or seen!