James Jay, a doctor and brother of American congressman John Jay, created an invisible ink system that used two chemicals. He wanted an ink that could not be revealed using heat, making it harder to expose. George Washington took the use of invisible ink a step further. 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. The first was made visible when exposed to heat, and the second was made visible when exposed to an acid. The British used two different types of invisible ink.
How was invisible ink used by Washington?ĭuring the American Revolution, invisible ink was an important method of communication for spies on both sides.
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