Imaging Locked Letter Collections

UH0218, virtually unfolding a sealed unopened letter from the Brienne Collection, DB-1538.

Welcome to our page of images and animations of letters including XMT scanned and virtually unfolded letters from the Brienne Collection, and models you can print out and fold at home.

Virtual unfolding is a computational process that analyzes CT scans of folded letterpackets and creates a flattened image of their contents. This process allows us to read the contents of sealed, historical documents – showing their text legible for the first time since they were sent some 300 years ago – without damaging the rare artifacts. Our virtual unfolding pipeline generates a 3D reconstruction of the folded letter, a corresponding 2D reconstruction representing its flat state, and flat images of both the surface of the writing substrate and each letterpacket’s crease pattern. For a full explanation of our findings see our Nature Communications paper. Our latest code can be found on Github.

Our foldable models have been developed so that you can try letterlocking at home, using pre-prepared guidelines that enable you to make replica models of the letters we studied for this article. Red and blue lines indicate whether creases are “mountain” or “valley”. The article contains step-by-step instructions for how to fold each one, and you can follow along with videos on our YouTube and Vimeo channels.

Normal Illumination

Art In Print

Texturized imaging with normal illumination

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The Brienne Collection. Images courtesy of The Sound & Vision (The Hague, The Netherlands).

Algorithmic Computation

by Cultural Heritage Imaging (CHI)

Photogrammetry

Italian Locked Letter

A letter from Maggioni to della Vernaccia sewn with cord and seal, Italy (1689). Unlocking History Historic Manuscript Study Collection. Imaged by Cultural Heritage Imaging using photogrammetry. (UH0089).

The Brienne Collection, The postmaster and postmistresses trunk, The Sound and Vision The Hague, The Netherlands

Reflective Transformational Imaging (RTI)

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“A computational photographic method that captures a subject’s surface shape and color and enables the interactive re-lighting of the subject from any direction. RTI also permits the mathematical enhancement of the subject’s surface shape and color attributes. The enhancement functions of RTI reveal surface information that is not disclosed under direct empirical examination of the physical object.” See examples of RTI used on letters from the Unlocking History’s Historic Manuscript Collection in the DoLL seal entry image gallery.

by Microtomography Research Group

X-ray imaging / micro-XMT scanning

“We’re x-raying history,” says Dr David Mills. Professor Graham Davis adds: “Who would have thought that a scanner designed to look at teeth would take us so far?”

Virtual Unfolding

CT Scan Cross-Sections, “Letterset 3”, virtually unfolding process 2016–2021

The following drawings, images. fly-through animations, and reconstruction videos show our latest virtual unfolding results, as well as some animations of the reconstruction process in progress. “DB” numbers (DB-0046, DB-0048, DB-1538, DB-1627, DB-1976, and DB-2040) refer to shelfmarks in the Brienne Collection held at Sound & Vision (The Hague, The Netherlands).

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“When we got back the first scans of the letterpackets we were instantly hooked,” says Amanda Ghassaei. “Sealed letters are very intriguing objects, and these examples are particularly interesting because of the special attention paid to securing them shut.”

— by the Unlocking History Research Group Algorithm engineers

Fly-through Animations

Fly-through of a scan of 10 letterpackets from the Brienne dataset, showing cross sections of the folded letterpackets.

Time delay integration, computed micro-tomography

High contrast TDI CT scan of a letter set 1, bundle of locked letters. March 2015.

High contrast XMT scan of Letterset 3. November 2016.

Courtesy of the Apocalpto Project. A video showing the layers of a high contrast TDI CT (Time Delay Integration, computed micro-tomography) test scan of a bundle of 20 locked letters. Using historic letterlocking formats, iron gall ink, a quill, and sealing wax, the #SignedSealedUndelivered team made up the batch of new letters for testing, writing secret messages inside, folding them using historic letterlocking formats, and sealing them with wax. The Unlocking History Research Group and their collaborators are developing the technology virtually reveal the contents and folding patterns to be revealed without tearing open the letters.