
31/07/2025
Invisible ink messages
What you need: half a lemon, paper and a thin paintbrush or cotton bud.
Challenge: squeeze half a lemon into a small bowl. Use the paintbrush or cotton bud to write your message or picture with the lemon juice. Leave for around an hour to dry. Use a heat source such a hair dryer to heat the paper and reveal the message.
Make the activity more enjoyable by designing a treasure map and let the children enjoy finding it.
What kids will learn: it may seem like magic to children, but it’s simple chemistry. Lemon juice is an acid but also contains water and sugar. Its normally clear in colour so we don’t see it, but when it is heated, the sugars in the lemon have a chemical reaction and turn brown.
For more great ideas to keep them happy over the summer holidays head to Families UK