Science Project: Hidden Messages Viewed: 4791
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Hidden Messages

Write an invisible message with flour and water and make it appear with iodine. Then use lemon to make it disappear again.

You need:

  • A few drops of lemon juice
  • 1 tablespoon flour (15 ml)
  • 2 oz. of water (60 ml)
  • cotton swabs
  • a paper towel
  • a few drops of iodine

What to do:

Mix 2 ounces of water with a tablespoon of flour. Write your message on the paper towel with a swab. When the message dries, it will be invisible. When you are ready to read it, use a swab to apply a few drops of iodine. Your message will appear in blue-black. Next, dab on a few drops of lemon.

What happens:

Your message disappears.


The iodine reacts with the flour, a starch, to form a new compound that appears as blue-black. When you apply the lemon juice, the ascorbic acid (Vitamin C) of the lemon combines with the iodine to make a new colorless compound. So, if you spill iodine on anything, you can use lemon juice to remove it. It also removes ink, mildew, and rust stains-from paper and cloth..

Be careful not to get the lemon juice or vinegar in your eyes, it will burn. Don't taste. Iodine is poisonous.