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