Never before in the history of espionage had an intelligence agency released top-secret formulas and methods. The CIA even stubbornly refused to release obsolete World War I formulas, let alone modern ones.

It was that discovery, along with the frustration that there was no book on the long hidden history of invisible ink, that inspired her to write about the subject. The result is Prisoners, Lovers, and Spies:  the Story of Invisible Ink from Herodotus to al-Qaeda (Yale University Press, 2014).

After extensive research on the subject, Mackrakis developed the book into a global history of secret communication from the ancient Greeks to the present. Pitched toward a general audience, the book uses stories about prisoners, scientists, lovers, and spies to trace the evolution of invisible secret writing while evaluating its impact on history.

“People’s lives depended on effective secret communication, yet during World War I and II, the Germans, who possessed sophisticated chemical communities, used primitive methods like lemon juice to communicate. [This] led to more sophisticated methods through an arms race between secret writing makers and breakers.”

There were, of course, lighter and more uplifting stories about secret communication. The book opens with the famous ancient Roman advisor for lovers, Ovid, who recommends using milk to write secret love messages. John Gerard, a Jesuit priest successfully escaped the dreaded Tower of London by using orange juice to communicate.

Additional stories reveal spies who used bodily substances like blood, urine, and semen to communicate invisibly while hiding secret ink in places such as the rectum and a tooth.

In addition to research examining recently released secret material from archives in England, Germany, and the U.S., Macrakis also experimented with invisible ink formulas and methods collaborating with chemistry colleagues. After reproducing the complicated Stasi invisible ink formula that uses a catalyst to speed up the reaction, she worked with Atlanta color chemist Jason Lye to experiment with some household items.

Lye and Macrakis are developing a series of videos about various inks and stories, the first two of which can be found here.