Invisible Ink

Your Challenge: Pretend to be a secret agent by writing a message in invisible ink! Lemon


1/2 of a lemon

Cotton swab




White paper


Here’s How:

  1. Squeeze some lemon juice into the bowl.
  2. Add a couple of drops of water into the lemon juice.
  3. Using the spoon, mix the lemon juice and the water together.
  4. Dip the cotton swab into the mixture and use it like a pen to write a secret message on the white paper.
  5. Let the message dry so that it becomes “invisible.”
  6. When you want to read the message, put the paper next to the light bulb in the lamp so that it heats up. Your message will magically appear and turn brown!


How It Works:

After mixing the lemon juice with the water, the juice is diluted and is almost impossible to see on the white paper when dry. However, when the lemon juice is heated, it oxidizes and turns brown (think about how apples turn brown when exposed to air too long–that is also oxidization!). Therefore, the lemon juice message is invisible until it’s heated up. How cool!

Fun Facts:

  • You can create a battery using a lemon!
  • A lemon’s sour taste comes from citric acid.
  • Other invisible inks are revealed by other chemicals or by UV light.


Related Careers:

Chemical Engineer, Chemist

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