History of Invisible Ink
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.
Ancient Times and the Renaissance
The history of invisible ink goes back more than 2,000 years and was used by the ancient Greeks and Romans. 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. 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. 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. Once painted on the shell of a hard-boiled egg, it would seep through and transfer the message onto the egg's albumen. The writing could only be seen once the egg was peeled.
During the Revolutionary War, both the British and the Americans used invisible ink. The British used both organic fluids and common sympathetic inks. 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.
But George Washington wanted something more, an ink that could only be revealed by a unique, specially formulated reagent. Sir James Jay answered the general's call. Jay, brother of American patriot John Jay and a physician that dabbled in chemistry, created a "sympathetic stain,” which he supplied to Washington. 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. 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. . . a common pocket book, or on the blank leaves at each end of registers, almanacks, or any publication or book of small value."
World War I
In contrast to the billion-dollar-budgeted intelligence agencies of today, when America entered the First World War, the CIA did not exist, and the FBI was barely 15 years old. The Office of Naval Intelligence coordinated the gathering of the country's intelligence.