Fire Writing With Invisible Ink

Fire writing with invisible ink
Reveal an invisible ink message with fire writing.

Fire writing is a fun science project. You write a message using invisible ink, let it dry, and then reveal the secret by touching a flame to the edge of the text. The message burns away, leaving the paper untouched except for the fire writing.

Fire Writing Materials

You only need simple materials for this project:

Write a Secret Message

  • First you need to prepare your “ink.” Mix potassium nitrate into a very small amount of water. Use just enough water to barely dissolve it.
  • Use a toothpick, cotton swab, fingernail, nail, etc. as your “pen.” Start writing the message or design at the edge of the paper. The flame burns in a continuous line, so avoid breaks between words or design elements. Cursive writing works, as do many pictures. You may wish to re-trace the message to make sure it is covered.
  • Let the paper dry completely. The message will be invisible.
  • Touch the edge of the paper where the message started with a flame from a lighter or match. The flame will burn away the message, leaving the rest of the paper intact.


You’re writing with fire, so use common sense and be prepared to extinguish the paper if the project gets out of control. This project is intended for responsible adults.

How It Works

Invisible ink works by subtly changing paper so that the message disappears when the ink dries but is revealed by a chemical or heat. Most chemicals used as invisible ink (e.g., lemon juice, saliva, vinegar) damage the paper. When the paper is exposed to heat from a light bulb or blow dryer, the damaged part darkens more than the untouched paper so the text appears. Theoretically, fire writing works with any message written with this type of invisible ink. But, there is a real risk of burning the entire paper and not just the message! This project uses potassium nitrate because it burns more readily than paper. The message burns away quickly enough to preserve the paper.

Looking for more fun? Give pyrography a try. This is a type of fire writing done using a sparkler.