A Greek Mystery

You would rather not damage historical objects, and then having a scanner that allows you to see right through various materials is a big help. This led restorer Benita Jansma to ask the CWI if an almost 450-year-old dictionary from the Regional Archive Alkmaar could be scanned using the FleX-ray Lab's X-ray scanner.

The Greek dictionary – dating back to 1580 – was bound around 1600. "Parchment strips were used to reinforce the binding, especially along the spine," says Jansma's colleague Lisette Blokker, coordinator of the service team at the Archive. These strips were made from cut-up old books that were no longer in use. "That happened a lot in the 17th century," Blokker explains. "For reinforcing new bindings, Catholic books that had been discarded after the Reformation were often cut up."

Rare

What makes the discovery special is that the used strips are rare. That's why the archive wanted to know what readable text was still on the strips. This could provide important clues about the age and origin of the cut-up book. However, the parchment strips were glued to the spine of the book block, and some also served as endleaf guards. Blokker: "After Benita removed the bindings from the book block – which was relatively easy as they were partially detached – we were able to read the outside of the strips." However, the inside remained unreadable because they were still glued to the spine of the book.

"We wanted to keep the book block intact and leave the strips in place if possible. But the discovery was so remarkable that we also found it important to read both sides of the used parchment." With this question, Jansma approached CWI: can you make the text visible on the inside of the adhesive strips?

Shadows and streaks

CWI researcher Francien Bossema from the Computational Imaging group explains that this was not a simple task: "We were only interested in the spine, but when you put the entire book in the scanner, you automatically scan through the rest of the book as well. This resulted in a lot of material: there was already twenty centimeters of thick paper between the spine and the side where the book opens. The X-ray radiation had difficulty passing through. That's why we eventually decided to open the book and thereby reduce the amount of material perpendicular to the spine." (see photo).

But that wasn't the only problem. Because the material was uneven, there was a lot of ink ‘behind’ the strips; namely, the ink from all the letters on the pages of the book that were stacked on top of each other. Bossema explains: "A CT scan digitally slices the object so to speak. To read text, the text must be precisely in one of those slices.

This makes a puckered page very difficult to read: the bumps all end up in different slices. Moreover, the ink from the other pages contained metals. The high density of these metals creates a kind of shadow, which prevents us from seeing what's behind. On a CT scan, this often creates streaks that hamper interpretation."

Much older

"In the end, we couldn't separate the different layers in such a way that the back of the strips became readable," says Blokker. "Anyway, we tried everything to keep the book intact."

Although it wasn't possible to reveal the hidden text through scans, the Alkmaar researchers are glad they had the opportunity to try at CWI. Ultimately, they decided to detach the strips. This allowed them, among other things, to determine the age of the cut-up book – it turned out to be much older than the Greek dictionary. An article about this has been accepted by a scientific journal.

Contact

Are you interested to learn more about our research, the FleX-ray Lab, or want to collaborate with us? CWI's Computational Imaging group can tell you all about this lab, contact them at seewhatsinside@cwi.nl