You will need:
- Half a lemon
- a few drops of water
- white paper
- heat source – an high watt incandescent bulb, radiator, hot plate or even a campfire.
- Squeeze the lemon into a small bowl and then mix in a few drops of water.
- Use the q-tip to write a secret message on the paper.
- Wait for the paper to dry.
- If you want you can use a pencil to write a decoy message as well.
- Hold the paper over the heat source (be careful not to get so close you burn yourself or your message)
- The lemon juice will oxidize and the message can be read.
If you don’t have a heat source available you can use Homemade PH solution. After the lemon juice is dry, paint the whole page with the cabbage juice. The writing will be a different colour from the rest of the page.
As an extension to either method, you can try other acidic liquids (apple juice, orange juice, vinegar) to see if they will also work.