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Cornstarch

What You Need

1 teaspoon cornstarch
Water
Measuring cup
Microwave-safe container
Spoon
Q-tips Cotton Swab
Paper
Two small bowls
Iodine
Eyedropper
Two small sponges
Lemon juice

What to Do
Mix the cornstarch and 1/2 cup water in the microwave-safe container. Stir until smooth. Heat in the microwave on high for fifteen seconds, stir, then heat on high for forty-five seconds more.
Dip the Q-tips Cotton Swab into the mixture. Write your message on the paper. Let dry.
In one small bowl, add ten drops of iodine to 1/4 cup water. Sponge the iodine solution lightly over the paper.

What Happens
The message appears in dark blue. (If the paper contains starch the paper may also turn light blue.) In the second bowl, pour 1/4 cup lemon juice and sponge it over the message. The message will disappear again.

Why It Works
The iodine reacts with the cornstarch to form a new compound that appears blue-black. The ascorbic acid in lemon juice combines with the iodine to form a colorless compound.

Bizarre Facts

A message in invisible ink, written beneath a one-sentence love letter on a postcard sent from Poland in 1943, vividly describes the horrific conditions in a Nazi death camp and makes an urgent request for supplies. The postcard is on display at the Yad Vashem Holocaust Museum in Jerusalem.
In Mexico, Parker Pen's advertising agency translated the phrase "won't leak in your pocket and embarrass you" by incorrectly using the Spanish word embarazar, which made the phrase read, "won't leak in your pocket and make you pregnant."

Close Shave
In 500 B.C.E., Histiaeus wrote a secret message on the shaved head of a slave, waited for his hair to grow back, and then sent the slave across enemy lines. When the slave's head was shaved, the message was revealed.

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