How To Make Invisible Ink - Corn Starch

Simple Invisible Ink Chemistry Project

Corn starch invisible ink is invisible on paper until it binds to iodine,
Corn starch invisible ink is invisible on paper until it binds to iodine,. denistorm, Getty Images

Do you want to write a secret message? Try making invisible ink! The writing for this invisible ink technique is done using corn starch. An iodine solution is used to reveal the writing.

What You Need

  • Corn Starch
  • Iodine
  • Water
  • Toothpick or Cotton Swab
  • Hot Plate or Stove
  • Paper

Make the Invisible Ink

  1. Essentially you want to make a thin corn starch gravy. You will write using the gravy, allow the writing to dry, then reveal the message using an iodine solution.
  1. 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.
  2. Mix about 2 T 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!
  3. 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.
  4. Let the paper air-dry.
  5. 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.

Tips for Writing Secret Messages

  1. You can use simple corn starch in water to write the message, but the writing won't be as invisible as it is using corn starch gravy.
  2. If the heat source is a problem, try using very hot tap water to hydrate the corn starch rather than using a stove or hot plate.
  1. Iodine binds to the starch molecules to reveal the message.
  2. Try using other starches instead of corn starch, such as diluted mashed potatoes or mashed cooked rice with water.
  3. Corn starch slightly alters the surface of 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.

    Did you enjoy this project? A related one is making disappearing ink. You can see the message when you write it, then it dries invisible and can be revealed again.