Make invisible ink

Make invisible ink

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Do you want to send someone a secret message?

You'll need some invisible ink!

What you need:

  • Paintbrush or cotton bud
  • White paper
  • Lemon juice
  • Small bowl
  • Lamp

Invisble ink equipment

Invisible ink materials

How to:

Dip your paintbrush or cotton bud lightly in the lemon juice and write a message on the paper. You only need a tiny bit of lemon juice on your paintbrush. Don't put too much on, otherwise the message will take a long time to dry!

Let the paper dry. You might be able to see the message at first, but as the paper dries it will disappear.

Lemon juice drying

Lemon juice drying

Once the message has disappeared, hold the paper up to a lamp, or other heat source and see what happens.

Invisible ink made visible

Invisible ink made visible!

It can take a while to get the hang of the right amount of lemon juice, but keep practicing and you'll be as good as a spy!

What's happening?

Lemon juice is a weak acid. The acid weakens the paper. When you hold the paper near a lamp, the heat burns the weak parts of the paper and turns it brown. Don't hold the paper in front of the lamp for too long, otherwise the rest of the paper might start to burn!

Try experimenting with other weak acids, such as vinegar, orange juice and even milk. Which one works best?

For more spy secrets, check out Planet Science CSI and find out how to discover which sneak left their fingerprints on the glass!

Curriculum information

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