🖊️ Invisible Ink
Write a secret message with lemon juice — invisible when dry, but heat the paper and your message appears!
🧰 What you need
Safety note: Ask an adult to handle the heat source. Keep paper moving — don't let it get too hot or it could scorch.
🔬 Steps
- 1
Mix lemon juice with a few drops of water. Dip the cotton swab in the mixture.
- 2
Write your secret message on white paper with the swab. Let it dry completely (5–10 min).
💡 Write in big, clear letters so your message is easier to read when revealed. - 3
Ask an adult to hold the paper near (but not touching) a light bulb or warm lamp.
💡 A hairdryer on a low setting also works. Keep moving the paper so it heats evenly. - 4
Watch your message slowly appear in brown! Show your secret message to a friend.
🧠 The Science
Lemon juice contains citric acid and carbon compounds. When you write with it and let it dry, the writing is nearly transparent — almost invisible. When you apply heat, the lemon juice oxidises — it reacts with oxygen in the air. The carbon compounds in lemon juice break down and turn brown, making your writing visible. This is the same browning reaction that happens when you grill toast or roast a marshmallow — the Maillard reaction at a gentler level!
📚 Related Lessons
- 🧼 Food Safety — Washing hands, covering food, and avoiding stale food protects us from germs and food poisoning!