What You Need:
- Juice of half a lemon
- Cotton bud
- White paper
- Lamp or light bulb
- Squeeze some lemon juice into the bowl and add a few drops of water.
- Mix the water and lemon juice with the spoon.
- Dip the cotton bud into the mixture and write a message onto a white paper.
- Wait for the juice to dry so it becomes completely invisible.
- When you are ready to read, heat the paper by holding it close to a light bulb.
While the paper gets heated, the letters written with the invisible ink become visible as the ink gets dark. Lemon juice is an organic substance that oxidises and turns brown when heated. Diluting the lemon juice in water makes it very hard to notice. Invisible ink can also be made using certain chemical reactions or by viewing certain liquids under ultraviolet light. You can use orange juice, honey, milk, onion juice, vinegar or wine instead of lemon juice to prepare invisible ink.