When the printing press made its debut in Europe in the 15th century, hand-written manuscripts went the way of eight track tapes and CD players—becoming unfashionable in the face of new technology. So early book binders cut up some of these older texts and used the paper to reinforce the spines and covers of the newfangled printed books.

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That practice has put researchers in another type of bind: To get to the valuable fragments built into these early modern books, they have to tear them apart. But according to Dalya Alberge at The Guardian a new technology is giving researchers a peek at the manuscript fragments without damaging the printed books.

Using macro X-ray fluorescence spectrometry (MA-XRF), Dutch researchers are able to scan the bindings to image the manuscripts hiding underneath. Erik Kwakkel, a book historian at Leiden University in the Netherlands tells Alberge that one in five early modern books contain the fragments. “It’s really like a treasure trove,” he tells Alberge. “It’s extremely exciting.”

Kwakkel writes on his blog that he got the idea of scanning the bindings when he was asked what technology that does not currently exist could radically change his field of study. He wrote an essay suggesting that accessing the “hidden medieval library” in the spines of books could reveal thousands of new text fragments.

Then he recalled that a colleague, Joris Dik at the Delft University of Technology, was doing something similar with paintings. Dik used MA-XRF to look beneath the layers of a Rembrandt self-portrait to see the earlier version below the paint. Kwakkel and Dik brought the MA-XRF machine to Leiden University and began experimenting on the books. After some adjustments, they found that the technology produced legible images of the manuscript fragments, lighting up the iron, copper and zinc used in medieval ink.

As part of the experiment, the team scanned 20 books. According to a press release, their discoveries include fragments from a 12th century manuscript from the early English historian Bede as well as text from the Dutch Book of Hours. The X-ray was also able to separate out texts that had been pasted on top of one another.

“Every library has thousands of these bindings, especially the larger collections. If you go to the British Library or the Bodleian [in Oxford], they will have thousands of these bindings,” Kwakkel tells Alberge. “So you can see how that adds up to a huge potential.”

But it may be a while before the hidden library is fully revealed. The current method is painfully slow, taking up to 24 hours to scan a book’s spine. The researchers hope that advances in X-ray technology will soon help speed up the process.