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During the American Revolution, invisible ink was an important method of communication for spies on both sides.

Ingredients and Supplies

¼ cup baking soda ¼ cup water Grape Juice Paper Something to write with- a cotton swab, toothpick, or paintbrush all work well.

Recipe courtesy of the book Invisible Ink: Spycraft of the American Revolution by John Nagy

Step 1 - Mix

Mix ¼ cup baking soda and ¼ cup water.

Step 2 - Wet your brush

Dip a cotton swab, toothpick or paintbrush into the mixture.

Step 3 - Write your message

Write a message on a white piece of paper and allow it to dry.

Step 4 - Apply the decoding stain

Dip a cotton swab into grape juice concentrate or any dark juice and paint it over the invisible message.

Step 5 - Reveal the message!

Wait for your message to appear.

How was invisible ink used by Washington?

During the American Revolution, invisible ink was an important method of communication for spies on both sides. The British used two different types of invisible ink. The first was made visible when exposed to heat, and the second was made visible when exposed to an acid. British intelligence officer Major John André instructed his agents to write an “F” for flame or an “A” for acid in the corner of a paper to indicate which should be used to expose a message.

George Washington took the use of invisible ink a step further. He wanted an ink that could not be revealed using heat, making it harder to expose. James Jay, a doctor and brother of American congressman John Jay, created an invisible ink system that used two chemicals. The first chemical was used to write the message, and the second chemical, when applied to the first, created a reaction that revealed the message. Washington encouraged his agents to write their invisible messages in the blank spaces of common books to make them less suspicious.

Interview with Revolutionary Spy Expert John Nagy