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The Art of Invisible Ink
During the American Revolution, both patriots and loyalists used invisible ink to protect their secrets. One of the most popular recipes involved mixing ferrous sulfate and water, which would only reveal the writing when heated or exposed to another chemical. George Washington himself wrote in 1779 about the importance of “sympathetic stain,” the era’s term for invisible ink. Modern researchers have identified over a dozen different formulas in use during the period, including lemon juice and milk. The Continental Army’s “Committee on Secret Correspondence” even trained officers in ink techniques. Letters containing invisible messages were often sent wrapped around innocuous family updates to avoid raising suspicion. Today, forensic analysis has successfully revealed hidden text in several surviving documents, confirming these early American spies’ resourcefulness.
Code Names and Nicknames
The use of code names and nicknames added another layer of security. Major John André, the infamous British spymaster, and Benedict Arnold, the American turncoat, often referred to themselves and others using numbers or aliases. For example, George Washington was sometimes “Agent 711,” while Benedict Arnold was known as “Gustavus.” Letters from the Culper Spy Ring, a network based in New York, routinely used code names for all members, including “Samuel Culper Sr.” and “Samuel Culper Jr.” This practice made intercepted letters confusing and challenging to decipher. Recent research from the Library of Congress archives has uncovered lists of these code names, showing how widespread the tactic was. The British also used code numbers, often referencing key players by three-digit identifiers. The dual systems created a high-stakes game of cat and mouse, with both sides constantly trying to crack the other’s cipher.
Complex Cipher Systems
Ciphers went far beyond simple substitution. Both sides developed intricate systems involving codebooks, grids, and even book ciphers, where words or letters corresponded to specific pages or lines in a popular book. The American “Culper Code Book,” for example, assigned numbers to hundreds of words and names. Instead of writing “British,” a spy might write “53.” The complexity of these ciphers was astounding given the era’s limited resources. According to a 2023 National Archives study, at least 20 significant cipher systems were in use between 1775 and 1783. Some letters took weeks to decode, and mistakes could have deadly consequences. Recent analysis using computer algorithms has managed to crack several ciphers that remained a mystery for centuries, shedding light on long-lost messages.
Hidden Messages in Margins and Between Lines
Not all secret messages depended on chemicals or codes. Creative writers sometimes hid messages in the margins or between lines of regular text. These “interlinear” notes were often microscopic and required careful reading or even a magnifying glass. In 2022, researchers at the Museum of the American Revolution discovered a letter from a soldier with a faint, slanted script running along the edge of the paper, containing details about British troop movements. Sometimes, writers would use a slightly different ink color or a finer pen, making the message nearly invisible to the casual reader. This method was a last resort when invisible ink was unavailable or too risky. The margin messages often included urgent instructions or rallying words, such as “Hold firm” or “Destroy after reading.”
Steganography: Concealing Within Art and Patterns
Steganography, the practice of hiding information within images or patterns, also made its way into Revolutionary correspondence. Some letters included odd drawings or flourishes that, when viewed under certain light or at an angle, revealed letters or numbers. Quilts and samplers, popular crafts of the time, sometimes contained secret codes stitched into their designs. In 2021, a textile historian found coded initials and dates sewn into a 1778 sampler, believed to communicate a meeting place for local patriots. Letters occasionally included elaborate doodles, which, according to experts at the Smithsonian, could contain hidden coordinates or references. These artistic codes required both skill and creativity, offering a layer of plausible deniability if intercepted.
Double Meanings and Wordplay
Writers were masters of double entendre. A letter might appear to discuss crops or family news but actually reference battle plans or supply routes. For example, “The corn is ready for harvest” could mean troops were prepared to march. In the infamous correspondence between Benedict Arnold and British Major André, seemingly mundane phrases masked plans for the surrender of West Point. Analysis by linguists at Yale University found that certain repeated phrases correlated with key events, suggesting a pre-agreed code. This method allowed for rapid, flexible communication with minimal risk of exposure, though it demanded that both sender and recipient be on the same page—sometimes literally.
Acrostics and First-Letter Codes
Some patriots got creative with acrostics, where the first letter of each line or paragraph spelled out a separate message. These codes could be hidden in poems, religious texts, or even love letters. One famous example, discovered in 2019 among the papers of General Nathanael Greene, contained an acrostic spelling “ATTACK DAWN” along the left margin. These were easy to miss unless you knew what to look for. Scholars say such hidden cues were especially useful for urgent or time-sensitive information. Acrostics sometimes combined with other methods, like invisible ink, for an added layer of protection. The British, too, adopted similar tricks, as revealed in captured correspondence from 1781.
Sealed and Folded Letters: Security by Design
Beyond the content, the very construction of a letter could hide secrets. Many Revolutionary letters were “letterlocked”—folded and sealed in complex ways to detect tampering. If a seal was broken or a fold disturbed, the recipient would know the message had been compromised. In 2024, the Massachusetts Historical Society used X-ray scanning to virtually “unlock” several unopened letters, revealing both their contents and clever folding techniques. Some letters included a false fold or secondary compartment, where the real message was tucked away. This physical security worked hand in hand with coded writing, making interception much riskier for both sides.
The Role of Women and Children as Couriers
Women and children often played a surprising role in transmitting hidden messages. Their letters were less likely to be searched, making them ideal couriers for sensitive information. Abigail Adams, wife of John Adams, wrote several letters containing veiled warnings and coded advice. In other cases, children’s drawings or schoolwork included subtle clues for sympathetic readers. A 2022 study at the University of Virginia uncovered references to women smuggling messages sewn into clothing or hidden in hairpieces. Their involvement was crucial, as they could move across enemy lines with less suspicion. The risks were real—if caught, they faced severe punishment or imprisonment—but their efforts contributed significantly to the Patriot cause.
Recent Discoveries and Ongoing Research
New hidden messages are still being uncovered. In 2024, a team at the New York Public Library used multispectral imaging to reveal secret text in a letter from Alexander Hamilton to a Continental Army officer. Digital forensics has become a powerful tool, allowing experts to see what the naked eye cannot. Scholars estimate that hundreds of Revolutionary War letters remain unexamined, some possibly containing vital intelligence. The National Archives continues to digitize and analyze new collections, and discoveries are often shared at annual conferences. Each revelation adds a new twist to what we thought we knew about America’s first spies and their incredible resourcefulness.
The Enduring Mystery of Revolutionary War Secrets
Despite centuries of investigation, many messages from the Revolutionary War remain undeciphered. Some letters feature codes or stains that modern researchers have yet to crack. The allure of a hidden message—waiting, perhaps, in a family attic or library vault—continues to inspire historians and amateur sleuths alike. As technology advances, experts hope to unlock more of these secrets, shedding fresh light on the war for independence. The ongoing search for hidden messages reminds us that history often whispers, rather than shouts, its most astonishing truths.
Besides founding Festivaltopia, Luca is the co founder of trib, an art and fashion collectiv you find on several regional events and online. Also he is part of the management board at HORiZONTE, a group travel provider in Germany.
