What you need:
- lemon or grapefruit juice
- a lamp or iron
- blank white paper
What to do:
- Start by talking about the uses of invisible ink (such as spying). Our hands and brains know how to write, even if we can't see what we're writing, and invisible ink can help prove it.
- Dip a Q-tip into lemon juice, grapefruit juice, or milk and write a message on blank paper.
- Let the paper dry. You won't be able to see what you wrote.
- Hold up the "invisible" message to a lightbulb, lightly rub against the bulb, and watch the message appear! For faster results, you can sandwich the paper between a folded paper grocery bag and rub with a medium-hot iron.