To avoid suspicion, Washington instructed his spies to write seemingly banal letters between the lines of their secret messages, or to inscribe them “on the blank leaves of a pamphlet. Washington would then pass it on to the Continental Army’s spymaster, Major Benjamin Tallmadge who in turn provided it to the members of the famous Culper Spy Ring: Abraham Woodhull and Robert Townsend. Jay, brother of American patriot John Jay and a physician that dabbled in chemistry, created a “sympathetic stain,” which he supplied to Washington. Sir James Jay answered the general’s call. Major John Andre, the chief British intelligence officer, had agents put a letter in the corner of their correspondence to inform the recipient as to how the hidden secret message could be developed for example, an “F” was placed in the corner of letters that could be revealed by fire, an “A” for those that needed the application of an acid.īut George Washington wanted something more, an ink that could only be revealed by a unique, specially formulated reagent. The British used both organic fluids and common sympathetic inks. The writing could only be seen once the egg was peeled.ĭuring the Revolutionary War, both the British and the Americans used invisible ink. Once painted on the shell of a hard-boiled egg, it would seep through and transfer the message onto the egg’s albumen. Giovanni Battista della Porta, an Italian polymath, developed a formula for invisible ink that consisted of an ounce of alum and a pint of vinegar. Invisible ink continued to be used during the Renaissance statesmen used it in their letters, and Ovid references the practice in his Art of Love. The first record of it comes from Pliny the Elder in the first century AD, who mentioned using the milk of the tithymalus plant as an invisible ink in his Natural History. The history of invisible ink goes back more than 2,000 years and was used by the ancient Greeks and Romans. The history of invisible ink is mainly the history of war, for it is during such times that intrigue, espionage, and spying is at its most vital and necessary. Sympathetic inks contain one or more chemicals and require the application of a specific “reagent” to be developed, such as another chemical or a mixture of chemicals. Sympathetic inks are more complicated chemical concoctions. The organic fluids alter the fibers of the paper so that the secret writing has a lower burn temperature and turns brown faster than the surrounding paper when exposed to heat. These organic invisible inks can be developed through heat, such as with fire, irons, or light bulbs, and some can be seen when placed under ultraviolet light. The former consists of the “natural” methods many of us tried our hand at as kids: lemon juice, vinegar, milk, sweat, saliva, onion juice, and even urine and diluted blood, to name a few. There are two categories into which invisible inks fall: organic fluids and sympathetic inks. #The invisibles say you want a revolution used seriesWhile the use of invisible ink has now been almost entirely eclipsed by modern technology, its history is incredibly fascinating, and today as part of our Man Knowledge series we’ll explore its use through time. So much so that the CIA bizarrely waited almost a century before revealing its most basic recipes to the public (information which was available on the web and to every Boy Scout), claiming even in the 90s that the material constituted a foundation upon which more modern tactics had been built and that invisible ink remained a viable tool for its agents. Such a low-tech espionage method may seem quaint today, but invisible ink was once a very serious business and an important tool in a spy’s bag of tricks. Dating from 19, the papers mainly contain recipes for “secret writing”–instructions for agents of the Office of Naval Intelligence (the CIA did not yet exist) on how make invisible ink. In April of this year, the CIA released its oldest classified documents and the last from the World War I era.
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