How to Make Invisible Ink

Cornstarch invisible ink is invisible on paper until it binds to iodine
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Do you want to write a secret message? Try making invisible ink! The writing for this invisible ink technique is done using cornstarch. An iodine solution is used to reveal the writing.

What You Need

  • Cornstarch
  • Iodine
  • Water
  • Toothpick or Cotton Swab
  • Hot Plate or Stove
  • Paper

Make the Invisible Ink

  1. Essentially you want to make a thin cornstarch gravy. You will write using the gravy, allow the writing to dry, then reveal the message using an iodine solution.
  2. If you don't have a pre-made iodine solution, you can make some by adding a teaspoon of iodine to about 10 teaspoons of water. Set the iodine aside for later.
  3. Mix about 2 Tbsp cornstarch with 4 tsp water in a pan. Heat, while stirring, until smooth. You can boil the mixture to make a gravy; just be careful not to burn it!
  4. Remove the cornstarch gravy from the heat. Dip a toothpick, small paintbrush, or cotton swab into it and use it to write your message on paper.
  5. Let the paper air-dry.
  6. Brush a small sponge, swab, or paintbrush dipped in the iodine solution over the paper to reveal the hidden message. The message should appear purple.


  1. You can use simple cornstarch in water to write the message, but the writing won't be as invisible as it is using cornstarch gravy.
  2. If the heat source is a problem, try using very hot tap water to hydrate the cornstarch rather than using a stove or hot plate.
  3. Iodine binds to the starch molecules to reveal the message.
  4. Try using other starches instead of cornstarch, such as diluted mashed potatoes or mashed cooked rice with water.
  5. Cornstarch slightly alters the surface of the paper, so another way to reveal the secret message is to heat the paper with the message over a flame or with an iron. The message will darken before the rest of the paper, revealing the secret.
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Your Citation
Helmenstine, Anne Marie, Ph.D. "How to Make Invisible Ink." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). How to Make Invisible Ink. Retrieved from Helmenstine, Anne Marie, Ph.D. "How to Make Invisible Ink." ThoughtCo. (accessed May 30, 2023).