Making invisible ink

National Research Council Canada

Invisible ink is used to write messages that are undetectable to the naked eye. Discover your inner “secret agent” by creating and revealing your own hidden messages in this fun and simple chemistry experiment.


  • Baking soda
  • Water
  • Bowl
  • Spoon
  • Toothpick, cotton swab, paintbrush or other tool for writing
  • White paper
  • Purple grape juice


  1. Add equal parts baking soda and water to bowl; stir with spoon. Make sure the baking soda dissolves well so as not to be too powdery.
  2. Dip toothpick, cotton swab or other writing tool into the “ink”; write a message on the paper.
  3. Allow the ink to dry completely until it is invisible.
  4. Paint over the paper with purple grape juice to reveal your message.

What just happened?

This is a classic example of an acid-base chemical reaction. The acid in the grape juice is neutralized by the baking soda (the base), producing a colour change on the paper to reveal your message.

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