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A page from one of Leonardo Da Vinci’s notebooks
September 29, 2023

The fine art of electrical engineering

Written By: Jason Daley


Most people who travel to Europe on vacation only get to see the works of old masters from behind thick ropes. But on a visit to the Teylers Museum in the city of Haarlem in the Netherlands in May 2023, Professor William Sethares was able to get very close to several drawings by Rembrandt. That’s because Sethares is part of a project using watermarks and mold marks to date the works of several artists. Rembrandt, for one, was guilty of rarely dating his work. By dating the paper on which a drawing is made, however, researchers can make an educated guess about when an artwork was created.

Professor William Sethares uses the watermark imaging system (WimSy) to examine the Rembrandt painting "Return of the Prodigal Son"

In the past, paper was made by hand on molds, each with unique idiosyncrasies and makers’ watermarks. These molds also tended to wear out on a fairly regular basis, meaning they were often replaced. Looking very closely at the “mold marks” and watermarks on the paper can help researchers group together artworks from the same batch, which could provide information about a date.

To do so, Sethares created a device he and his collaborators call a watermark imaging system (WimSy). The artwork is placed on a lightbox, then photographed in multiple ways, gathering surface images, raking light images, and transmitted light images of the paper. Using software developed by graduate student Elisa Ou, the system can isolate the paper and any watermarks or mold marks created by the papermaker. These can then be used to match pieces of paper made on the same mold, which could help determine a date.

In this photo, Sethares is using WimSy to photograph a drawing made in preparation for Rembrandt’s painting “Return of the Prodigal Son,” which has not been definitively dated. Besides Rembrandt, Sethares has also used WimSy, currently being tested in European museums, on some of Leonardo da Vinci’s very jumbled notebooks.

Top image caption: A page from one of Leonardo da Vinci’s notebooks from around 1510. In the upper part of the image there is a faint watermark of an eagle, which Professor William Sethares matched with eagles from the Arundel Codex, thus confirming relationships between the two codices. Image courtesy of William Sethares.