Create your own secret

Material:

- lemon
- sheet of white paper
- ear swab,
- knife,

Instruction:

Ask parents to cut with a knife lemon and squeeze lemon juice.

Then use a cotton swab to  write "secret message" on a card with lemon juice.

You have to let the card dry, then put on the hot burner (be carefull do not burn the card!).

Explanation:

When the card is dry letters will be invisible to the eye. Only with the temperature you can read this text. It is because of the acidic juice weakens the paper. When the paper is heated, the color is getting more dark. In the place where the lemon juice works, it is going faster.