During the Revolutionary War, General George Washington waged a secret war against the British, relying on information from a network of spies operating behind enemy lines. Acquiring intelligence about troop movements, supplies, and battle plans was his highest priority. Because such field reports could not be overtly communicated to him, placing his agents at great risk, Washington used an 18th-century form of invisible ink known as “sympathetic stain.”
Invented in England by Dr. James Jay, the brother of American patriot John Jay, the stain required one chemical for writing a message and a second to develop it. In a letter to his chief spy handler, Major Benjamin Tallmadge, Washington described the proper technique for making use of the disappearing ink: “All the white Ink I now have … is sent in Phial No. 1 by Colo. Webb. the liquid in No. 2 is the Counterpart which renders the other visable by wetting the paper with a fine brush after the first has been used and is dry.”
Washington, who personally decoded much of this correspondence, instructed his agents to write “on the leaves of a pamphlet … of a common book, or on the blank leaves at each end of registers, almanaks, or any new publication of small value or sent in a familiar letter on domestic matters … interlining with the stain his secret intelligence.”
Upon realizing that the British also possessed the secret of invisible ink, Washington further advised that agents should “write a letter in the Tory stile, with some mixture of family matters and between the lines and on the remaining part of the Sheet communicate with the stain the intended intelligence; such a letter would pass through the hands of the enemy unsuspected.”
The “sympathetic stain” gave George Washington an important advantage in fighting the British. Nevertheless, communications made with invisible ink sometimes fell into enemy hands. It is estimated that the British intercepted and decrypted over half of America’s secret correspondence during the war. How will your message go undetected ...?