Letterlocking

Kerstboom envelope:This envelope is the winner of the Envelope Design Contest held during the Dutch Convention 2015.

Unlocking History is the name for a group of conservators, paleographers, literary scholars, historians, publishers, book-artists, imaging experts, engineers, and scientists who are interested in the historical practice of letterlocking.¹

Letterlocking was “an early form of communication security.”

Letterlocking refers to the technology of folding and securing an epistolary writing substrate to function as its own envelope – a vital communications technology before the invention of the mass-produced envelope in the 19th century.²

The Spiral-Locked Letters of Elizabeth I and Mary, Queen of Scots

On the eve of her execution for treason in February 1587, Mary, Queen of Scots, penned a letter to King Henri III of France and secured it with a paper lock that featured an intricate spiral mechanism. So-called "letterlocking" was a common practice to protect private letters from prying eyes, but this spiral lock is particularly ingenious and delicate because it incorporates a built-in self-destruct feature.³

Four letterpackets from Renaissance Europe

Computational flattening algorithms have been successfully applied to X-ray microtomography scans of damaged historical documents, but have so far been limited to scrolls, books, and documents with one or two folds. The challenge tackled here is to reconstruct the intricate folds, tucks, and slits of unopened letters secured shut with "letterlocking," a practice-systematized in this paper-which underpinned global communications security for centuries before modern envelopes. We present a fully automatic computational approach for reconstructing and virtually unfolding volumetric scans of a locked letter with complex internal folding, producing legible images of the letter's contents and crease pattern while preserving letterlocking evidence. We demonstrate our method on four letterpackets from Renaissance Europe, reading the contents of one unopened letter for the first time. Using the results of virtual unfolding, we situate our findings within a novel letterlocking categorization chart based on our study of 250,000 historical letters.⁴

The Envelope and Letter Fold Association

Learn about how to do LetterLocking at Envelopes and Letter folds.

1. Letterlocking.

2. The Dictionary of Letterlocking (DoLL).

3. Quilette, J. (2021). Mary, Queen of Scots, sealed her final missive with an intricate spiral letterlock. Ars Technica.

4. Dambrogio, Jana, et al. “Unlocking History through Automated Virtual Unfolding of Sealed Documents Imaged by X-Ray Microtomography.” Nature Communications 12, no. 1 (2021): 1184–1184.