Lemon juice is acidic and weakens paper. When paper is heated, the remaining acid turns the writing brown before discoloring the paper.
Time Required: A Few Minutes
- Squeeze lemons to obtain their juice or obtain bottled lemon juice.
- Use the juice as 'ink' by applying it to a stick or paintbrush and writing on paper.
- Allow the paper to dry.
- When you are ready to read your invisible message, hold the paper up to sunlight, a lightbulb (recommended), or other heat source.
- The heat will cause the writing to darken to a pale brown, so your message can now be read.
- Another way to read the message is to put salt on the drying 'ink'. After a minute, wipe the salt off and color over the paper with a wax crayon to reveal the message.
- Experiment with other juices. White wine, orange juice, vinegar, and apple juice all work well, too.
- A cotton swab makes an excellent disposable 'paintbrush'.
- The writing turns brown because the weakened paper burns before the rest of the paper. Be careful not to overdo your heating and ignite the paper!
What You Need:
- Lemon or Lemon Juice
- Sunlight or Heat Source
- Paintbrush or Stick