Virtual letter opener unlocks new research area

Nadine Akkerman_Letterlocking

Within the NWO project ‘Signed, Sealed, & Undelivered’, an international, multidisciplinary team of researchers developed a new technology to read folded letters without opening them. With the Nature Communications article in which they describe this technology, the authors have put research into how letters are folded on the map, says project leader Nadine Akkerman from Leiden University.

It is 31 July 1697. Jacques Sennacques from Liege writes to Pierre Le Pers in The Hague that he needs an official death certificate as quickly as possible for a certain Daniel Le Pers. As the invention of the envelope will not take place for another 150 years, he folds the letter in such a way that this also immediately functions as a sealed envelope, and sends it. However, the letter cannot be delivered and ends up unopened in the trunk of postmaster Simon de Brienne and his wife, postmistress Maria Germain. Now, more than 300 years later, it has at last been read without disrupting the ingenious manner of folding, also called letterlocking.

Read the case


The computer scientists came with a draft algorithm and tested this on a letter. Subsequently, our contribution as handwriting and literary experts was to assess which pieces of the puzzle had not yet been put in the right place. The computer scientists used that information to further refine the technique.

Nadine Akkerman