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Polygons to the rescue: ‘virtually unwrapping’ an ancient scroll long thought destroyed

Ein Gedi is the site of a large Jewish community of antiquity in Israel, dating from the late eighth century BCE. It was destroyed by fire ca 600 CE, including the synagogue and all its relics and sacred items. Excavation in the 1970s uncovered the synagogue’s Holy Ark. When it was opened, it was found to contain burned and crushed fragments of ancient parchment scrolls.

Since the Ein Gedi settlement stemmed from the Essene group responsible for the Dead Sea Scrolls, these charred scrolls were probably also important. But they were so badly damaged, unrolling them to read them just wasn’t an option. At a loss for what to do, conservationists left the fragments in archival storage until scientists could figure out technology that would let us read the scroll fragments without unrolling them.

Now, just such a technology has appeared. It’s called “virtual unwrapping,” and it takes place in four computational steps. In this case, researchers first ran a high-resolution micro-CT scan of the scroll fragments, which look like nothing but a piece of burned stick from the bottom of a fire pit. Then the researchers plugged that X-ray data into a suite of software that does “volume cartography.” The software detects the surfaces of the scroll based on their expected geometry, renders the page surface into polygons, and then looks for changes in brightness on the surfaces identified as pages. Dense areas — ones covered in metal-rich ink, for example — appear brighter on the scan. The software checks its own estimation of the scroll’s physical structure, using those differences in brightness to be sure it’s staying on the layer it thinks it’s on.

“When the segmented geometry drifts from the skin surface,” the authors explain, “the surface features disappear. When the skin is accurately localized, the surface detail, including cracks and ink evidence, becomes visible.” Finally, the software flattens the rolled-up text, showing the words as they would appear on a two-dimensional surface. What results is what the authors call a “master view:”

They needed a noninvasive method, the team writes, because even the most delicate imaging technique “necessitates physical handling of the friable material.” Normally, handling would have meant transporting it from its home in archival storage at the Israeli Museum in Jerusalem, but the curators weren’t thrilled about that. The scrolls had been burned to charcoal, and they disintegrate further at every touch. Rather than entrust such a fragile artifact to the hands of anyone else, the museum curators used an in-vivo CT scanner. This way they could do noninvasive scanning in house, without mounting the sample for scanning. “The curators do all the work in handling the objects, and they are experts,” explained lead author and computer scientist Dr. W. Brent Seales.

Coauthor Seth Parker compared this work with the CT scanning used to find the inscriptions buried inside the Antikythera mechanism. Parker remarks that their project builds on that basic technology to create a highly configurable “software pipeline,” tunable so that it can image many types of artifacts. “Ink-based texts show text as visual (luminance/color) contrast, but metal scrolls with etchings show text as morphological contrast (a height difference within the local area),” Parker said.

Using voxels on the order of a micrometer per side, the software establishes a baseline for what’s a letter and what’s negative space. “We’re currently focused on page-like materials (e.g. books, manuscripts, scrolls, etc.),” said Parker, “but the principles can be applied in a lot of places. It really comes down to exactly what features of the object you want to look at.”

The reward for all this work is the clear, legible text of a really old version of two chapters of Leviticus. While Jewish writers of the day didn’t specify vowels, the consonants in these chapters are “letter-to-letter identical” to the so-called Masoretic text, the authoritative medieval version of the Hebrew Bible. This represents the earliest known evidence of an exact version of that text, and the earliest known example of a Pentateuchal scroll outside of the Dead Sea Scrolls. It doesn’t change anything about how the Bible is currently published; in fact, this translation confirms many others. Coauthor Michael Segal explained: “There will not be any differences in translation, since the text is identical to that which is generally translated in Jewish and Christian Bibles.”

Seales and Parker still haven’t taken their eyes off Herculaneum. Seales succeeded in 2009 in working out the physical structure of the ruffled layers of papyrus in a Herculaneum scroll. While the En-Gedi scrolls have just a few layers, the scrolls from Herculaneum are probably hundreds of layers deep, written with metal-rich ink. Seales remarked that the materials they work with are of low density: papyrus, leather, parchment, and the like, so their process should be extensible to those scrolls.  “Herculaneum was our first passion,” said Parker, and Seales added that it “remains a huge hope of mine.”

“There’s a lot of things in the works,” said Parker, “but we are still and always will be dedicated to reading a full Herculaneum scroll.” Seales added that the suite of software programs he used, called “Volume Cartography,” will become open source next year as part of their NSF grant release.

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