No Secret Agent can go without invisible ink. This is a simple invisible ink recipe using lemons.
Suitable for kids aged 5+ (with adult supervision)
- Lemon Juice
- Heat Source: direct sunlight or a light globe. Use an iron, candle or oven as a last resort under strict adult supervision.
- Cotton swab, fine paintbrush or matchstick
This experiment involves the use of a heat source that could result in a burn if not used correctly. The heating step must be performed by an adult only.
What to do:
- Lemon juice is the invisible ink (freshly squeezed lemon juice is best, but bottled lemon juice also works).
- Use a fine paintbrush (cotton swab or matchstick) to apply the lemon juice to the paper and write your secret message. A visible message or drawing be written on the paper to further encrypt the message.
- Wait for the paper to dry so your secret message becomes truly invisible. This could take a while.
- When you are ready to reveal your secret message, hold the paper to a heat source (direct sunlight or a light bulb). If the message doesnt appear use a stronger heat source like an iron, oven or candle under strict adult supervision. Be careful not to set your paper on fire.
- The heat causes the lemon juice writing to turn a pale brown, revealing your secret message.
- Experiment with other liquid acids, like white wine, coke, honey solution, milk, orange juice, vinegar and apple juice.
Why is it so?
The acid in lemon juice begins to break down and weaken the paper fibers. When the paper is heated, the weaker lemon-soaked paper breaks down further. The lemon juice oxidizes and turns a brown-yellow colour. And the secret message is revealed.