18th Century

James Jay’s Invisible Ink

Have a drink with: James Jay
They’ve given you a number and taken away your name

Ask him about: passing notes in class

Invisible Ink

With the recent news that Congressional Republicans have rolled back broadband protections on the harvest and sale of Internet search data by service providers, information on how to protect the privacy of your Internet existence is in high demand.

One of the words that most often comes up in this space: encryption. One of the cornerstones of modern information security is the ability to protect information in an algorithmic shield. But if you ask Revolutionary War spies about their information security program, they’d have one thing to tell you: scrambling is good, but hiding is better.

In a tale of espionage, technology, and the economy of intellectual property, Sir James Jay – whose older brother John was the first Chief Justice of the U.S. Supreme Court – was known to have worked on invisible ink technology during the Revolutionary War.

Jay developed a “sympathetic ink” which would disappear once put to paper, and which would not reveal its message unless a specific corresponding reagent was applied. John Jay told George Washington about his brother’s ink, and managed to convince him to provide some. Washington was amazed:

“It is in my power, I believe, to procure a liquid which nothing but a counter liquor (rubbed over the paper afterwards) can make legible — Fire which will bring out lime juice, milk and other things of this kind to light, has no effect on it. A letter upon trivial matters of business, written in common ink, may be fitted with important intelligence which cannot be discovered without the counterpart.”

The famous “Culper Ring” of Revolutionary spies were worried about important documents being intercepted, so in addition to using code, assigned numbers and aliases, they wrote messages using Jay’s mysterious “white ink.” (The Brits had similar technology also; but one of the benefits of invisible ink is that you can rely on the idea that your enemy might not know you have access to it).

Subsequent analysis has suggested that Jay’s formula was a solution of tannic acid, with ferrous sulfate used to reveal the text.

Oddly, Jay was never paid for his work. Well after the close of the war, Jay went to President Thomas Jefferson and Congress, and argued he was due $20,000 in exchange for a botched 1778 loan to the U.S. – a sum that had put him in dire straits, and the payment of which would surely be a nice gesture to recognize him for his services and technology. Claiming that the ink formula had been invaluable during the war and would no doubt provide public benefit on a going-forward basis, Jay asked for compensation.

Congress was animated but uncertain on the issue: some Congressmen felt Jay should be paid for undeniable service to the nation; others said it was “absurd to vote away money for a thing they did not and could not understand;” still others worried about leaks to foreign governments; and besides: why worry about hiding messages when Washington is one giant sieve, information-wise?

In classic governmental fashion, the Congressmen resolved: “That it shall be lawful for the President of the United States to obtain, by purchase, at a reasonable price, the exclusive right, on behalf of the public, of the system invented by Sir James Jay, as submitted by him to the Executive Department of Government: provided, in the opinion of the President, it will be of public utility and importance to possess the same.”

Of course, just because something is deemed lawful doesn’t mean that it will happen. Politics, gymnastics and the passage of time meant that Jay received plenty of compliments, but died uncompensated.


Fun Facts:

Author Kristin Macrakis notes that secret writing technology really didn’t come into its own until the 20th century, and has historically received far less attention than its big brother cryptography. And while codebreaking may be more crackling and suspenseful, any kid who’s ever tried lemon juice and a light bulb can attest to invisible ink being enough to make you feel just a little bit like James Bond. Wanna feel like James Bond? Of course you do. Try this one at home!

Some puzzles really do stand the test of time: the famous Kryptos sculpture at CIA headquarters in Langley remains unsolved more than 25 years after it was unveiled.

17th century data security practices, or: An-cay oo-yay ead-ray is-thay?

There are many ways to hide messages in plain sight, and not all of them involve invisible ink: the ten-dollar word encompassing all forms of hidden communication is “steganography.” Encryption makes a message unreadable; steganography hides it entirely. This has become especially relevant in the modern information security context, where attackers can use things like malware to hide threats in otherwise unsuspecting places.

In 18th century France, the Count Vergennes (who, yes, you may picture in your mind as Count Rugen) developed an elaborate artistic code to hide messages within the filigreed letters of introduction visitors would bring to announce themselves to King Louis XVI. A French official would research a visitor’s background, and create an elaborate decorated calling card from the resulting information. Lines, dots, flowers and paper color communicated important details: was the visitor old or young? What was the purpose of their visit? Were they attractive, lecherous, well educated, a big spender, a security risk, Catholic? The card was unsealed and lovely, arousing very little suspicion; and the bearer was instructed to make an appointment with Count Vergennes to schedule royal audience, at which point he would silently decode the message and make recommendations – to delay someone in Paris to encourage them to spend more money, or even to have police keep an eye on their whereabouts.

Additional Reading:

Kristin Macrakis, Prisoners, Lovers, & Spies: The Story of Invisible Ink from Herodotus to al-Qaeda

Kaveh Waddell, The Long and Winding History of Encryption, The Atlantic, January 13, 2016

Jennifer Wilcox, Center for Cryptologic History – National Security Agency, Revolutionary Secrets: Cryptography in the American Revolution

Podcast @ Scientific American, Invisible Ink and More: The Science of Spying in the Revolutionary War