PRISONERS, LOVERS, AND SPIES: THE STORY OF INVISIBLE INK FROM HERODOTUS TO AL QAEDA
By Kristie Macrakis
Yale University Press, $27.50, 392 pages
At hand is an utterly fascinating account of how secret writing has evolved from wartime messages written on the shaved head of a slave so he could slip undetected through enemy lines, to spy communiques concealed in pornographic postings on the Internet.
The author, Kristie Macrakis, knows her territory. A professor at Georgia Tech, she is a historian of science as well as espionage. Her earlier books include the well-received "Seduced by Secrets" on the Stasi, the former East Germany security agency.
She has cast a wide research net, trolling up lively evidence not only in intelligence archives, but also in literature. Indeed, one of the first printed references to secret writings she found was in "The Art of Love," a "racy manual on seduction" by the Roman classical poet Ovid. If necessary, how could lovers exchange private notes? The author cites what she found to be "the earliest reference" to a form of secret ink:
"A letter too is safe and escapes the eye, when written in new milk: touch it with coal dust, and you will read."
Most assuredly, modern secret writing is a bit more complex, and the account related by Ms. Macrakis makes clear the importance of spymasters allying with chemists to conceal their secrets.
For centuries, a basic ingredient in secret writing was liquid obtained from "gallnuts" — nutlike swellings on an oak tree, produced when parasites such as wasps lay eggs on the bark. Much of the liquid produced in the swelling is tannic acid. The ancients discovered that mixing the liquid with iron sulfate produced black writing inks that were a staple for artists and writers for centuries.
Users also soon discovered that a message written with only one ingredient could not be seen, but brushing over it with the second ingredient "made it appear black just as if the two had been mixed from the start."
Such is the basis for much secret writing over the centuries: a liquid used as an "ink" that is invisible until brought to life by a reagent, either another chemical or heat. Over time, of course, certain ingredients became widely known, ranging from citrus juices (orange and lemon) to urine, semen and cobalt.
During the American Revolution, physician James Jay (older brother of Founding Father John Jay) developed a secret-writing system whose ink was "lost to history," as Ms. Macrakis writes. Whatever its composition, the ink was used in communiques to and from Silas Deane, based in Paris for the Continental Congress, earning him the distinction of being "the first American agent to use invisible ink." Because of the "peculiar nature" of the "services rendered," Jay did not ask for payment.
During World War I, the British-German competition to detect one another's secret inks was as intense, in its own way, as the fighting on the French battlegrounds. As Ms. Macrakis tells us, "It is probably no exaggeration to say that more happened in the development of secret ink during World War I then during the previous three hundred years."
The German Secret Service disguised its invisible inks in such household items as medicine, soap, toothpaste, mouthwash and perfume. One concealment technique: smear a paste containing the ink on the top of black socks. Once in enemy territory, the agent could soak the tip of a sock in cold water, producing a light-brown liquid the color of a scotch whiskey.
The competition resumed at the outbreak of World War II. British intelligence moved swiftly to set up a monitoring system for international mail. A key field station was in Bermuda, a transit point for correspondence between the United States and Europe. The British staff was predominantly female, with more than 800 women. Why the imbalance? Because women seemed to be the best "trappers" — i.e., adept at spotting secret writing. (A British official wrote that "by some quirk in the law of averages, the girls who shone in this work had well-turned ankles." To which Ms. Macrakis rightly sniffs, "Apparently, no one went on to research male sexism in the British intelligence community.")
When America entered the war, Washington formed a similar screening operation. However, civil libertarians in the Roosevelt administration feared public outcry against snooping. The chore was assigned to the Office of Censorship, headed by a respected Associated Press executive, Byron Price.
So how could the operation be masked? Price's original idea was to name it the "Department of Forestry and Grazing." But he settled on the equally unrevealing "Technical Operations Division," or TOD, tucked away in a windowless, highly guarded top-floor suite in the Federal Triangle. It employed 560 people at war's end.
Both systems worked. By the time peace came, British censorship had intercepted 219 "significant secret-writing communications," and the United States an additional 120. There were successful prosecutions in both countries.
The last secret writing technique is called "steganography," meaning "hidden writing," a word coined by a 15th-century abbot. Militant jihadists on the Pakistan-Afghanistan border found a way to embed message in text files on porn sites. I apologize that my technical knowledge is so limited that I shall not even attempt a further explanation.
Kristie Macrakis concludes her book with an 11-page appendix of "Fun Kitchen Chemistry Experiments" — how to do secret writing at home. Horrified Yale University Press attorneys insisted on attaching a "do these at your own risk" disclaimer, so I shall mention only one seemingly harmless method. Use tonic water (omit the gin) and write on a brown paper bag. Read with a black-light bulb that you can buy at the drugstore.
Now, a secret writing recommendation: Rub your index finger over the last three words of this review. Read this book.
Joseph C. Goulden is the author of 18 nonfiction books.