Invisible ink

Lemon juice doubles as invisible ink, making it perfect for a quick bit of science fun at home.

How to try it:

• Write a secret message or picture using lemon juice on a piece of paper.

• Leave it to dry completely — around 20 minutes should do.

• Parent step: carefully run a hot iron over the paper to reveal the secret message. Other heat sources, such as a hair dryer, can be used but an iron works best.

Perfect for budding spies and secret agents — or for hiding secret clues in treasure maps, spell books and other mysterious creations.