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How To Make Invisible Ink - Corn Starch

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The writing for this invisible ink technique is done using corn starch. An iodine solution is used to reveal the writing.
Difficulty: Average
Time Required: 15-30 minutes

Here's How:

  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.
  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 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!
  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.

Tips:

  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.
  3. Iodine binds to the starch molecules to reveal the message.
  4. Try using other starches instead of corn starch, such as diluted mashed potatoes or mashed cooked rice with water.

What You Need

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

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