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Email and instant messaging have replaced the writing of physical letter or notes. It is still important to equip our fellow readers with knowledge of creating invisible ink in case there is a need to send secret letter when all electronic devices are broken down. No fancy UV light is required to recreate this secretive writing method invented 2,000 years ago. All you need are:
- Lemon
- Saucer
- Water
- Teaspoon
- Toothpick
- White paper
- Lamp
- Squeeze the lemon juice into the saucer.
- Add a tablespoon of water and mix well with the spoon.
- Dip the toothpick into the lemon juice mix.
- Write a message on the white paper (thick paper works better) with the toothpick.
- When the paper dries, the writing will be invisible.
- Heat the paper by holding it near a light bulb (you can use heat from a stove or candle for faster result).
- Invisible writing will slowly turns brown and visible when the paper is heated up.
What happened to the lemon juice?
The juice of lemons has compounds of carbon which do not have colour when dissolved in water. However when the lemon juice is heated up, there is a change in its chemical properties. The carbon compound loses its electrons and breaks down. The oxidation process turns the invisible juice black. Paper is made of cellulose fiber which will also turns brown when it’s burnt. After the paper absorbs the lemon juice as part of it, the invisible writings turns darker faster.
