Since the scrolls’ discovery, people have tried various physical efforts to ferret out their contents. The results were largely disastrous. The most successful attempts were made in the 19th century, when about 300 of them were peeled apart by machine. This endeavor resulted in fragmented, layered sheets of brittle papyrus with visible, but largely illegible, writing on the black-as-charcoal surface.

These fragments are uneven and warped, which obscures and distorts the text even further. In addition, it’s practically impossible to tell where one layer of a papyrus wrap ends and another begins. This creates a jumbled mass of letters and words that is difficult to unscramble and understand. Finally, the top layers can hide three, four, or five — no one really knows how many — underlying sheets of writing. Thus, a non-invasive method for extracting the hidden text is needed.

Painstaking efforts to piece together meaning from these open fragments have resulted in limited success.  Papyrologists have identified some texts as important works by Epicurus and his followers, including the poet and philosopher Philodemus of Gadara (see Oxford Bibliographies), and a recent laboriously analyzed papyrus turned out to be a Latin text by Seneca the Elder. In 2008 the Institut de France granted Dr. Seales and his team permission to study a fragment in their collection. The investigation led to the discovery of lead and other trace elements in the ink and represented the first ever instance of reported heavy metals in Herculaneum writings.  The complete results were published in 2009 in the proceedings of the Academy’s annual program Lire Sans Détruire les Papyrus Carbonisés d’Herculanum. Although the quantities were very small, the presence of metal-based ink, a surprising discovery that Dr. Seales was first to report, suggested that imaging methods based on absorption, such as micro-CT scans, could produce contrast at the site of the writing.  As a result of the knowledge gained from the fragment study, the Institut de France granted Dr. Seales permission to scan two intact Herculaneum scrolls on site using a micro-CT machine.

View closed scrolls

EDUCE: Imaging the Herculaneum Scrolls

Following the fragment study, Dr. Seales and his team traveled to the Institut de France in 2009 to perform the first-ever micro-CT scans of completely closed Herculaneum scrolls. These micro-CT images revealed much that was previously unknown about Herculaneum papyri and definitively proved it was possible to see, without physically opening the scrolls, every papyrus strand and fiber inside them, even the grains of sand trapped in tiny creases. This study provided the first ever volumetric images of a Herculaneum scroll, revealing the complexity of the internal structure and the utter scale of the task at hand. The scrolls were so tightly wrapped that in many places the scans showed little to no separation between layers, and the team learned much in their attempt to process the images.

First, naive application of existing segmentation techniques does not address the unique problems that Herculaneum scroll strata and that of other ancient manuscripts present. Depending on the type of material being scanned, scroll strata can appear fuzzy or almost indistinguishable due to time-induced distortion, disintegration, or other deformations of the writing medium. Some commonly used writing surfaces like papyrus can fray easily over time, while others like parchment made from animal hide often bubble or suffer holes. Such local defects in the surface make it difficult to visually follow a layer through the volume across the CT slices.  Furthermore, undulations in and fusions of the scroll strata can cause the separations between layers to disappear and reappear at random, and tracking a single stratum through an entire scan becomes even more difficult as layers seem to merge together and then separate later on in the scan. The ink used to pen Herculaneum texts poses another challenge. Ancient writers used a mixture called “carbon black” which, when exposed to micro-CT scans, attenuates the x-rays the same way the carbonized papyrus, an carbon-based material on which it sits, does. Therefore, the ink of Herculaneum texts does not show up as readily in CT-scan data as that found in medieval texts, which usually contains metallic elements that are much denser than the writing surface and attenuate x-rays differently. In addition to these material-specific problems, micro-CT introduces its own anomalies and deformities into scan results, such as beam hardening, streaking, and ring artifacts, that must be compensated for in the final raw CT slices. These extra artifacts can make image processing much more difficult on scroll CT data and are heavily dependent upon the parameters selected at the time of the scan.

This confluence of challenges makes Herculaneum scrolls the most difficult digital restoration case encountered by Seales and his team.  Following the 2009 micro-CT scans, the team spent the next few years prototyping a step-by-step computational approach for processing micro-CT data that would produce a digital representation of unseen text rich enough to enable textual scholarship, a process called “virtual unwrapping.” These advances address most, if not all, of the segmentation challenges presented by Herculaneum materials. Most recently, the team successfully developed and deployed a machine learning algorithm that is powerful enough to reveal the carbon ink that has proven so stubborn to researchers.

Innovative Machine Learning Tool Reveals Carbon Ink https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0215775)