Summary

Researchers used lead-containing ink, tomography and virtual unrolling to detect writing in carbonized scrolls without opening them. The laboratory demonstration could improve efforts to read fragile scrolls buried by the eruption of Vesuvius.

Researchers have demonstrated a way to make writing inside burnt, rolled-up papyrus easier to detect without physically opening the scroll. The method combines lead-containing ink with three-dimensional tomography and software that virtually unwraps the damaged material.

The experiment used laboratory-made scrolls rather than originals from the ancient Roman town of Herculaneum. Its immediate result is a method demonstration: a chemical signal from the ink can help distinguish writing from the papyrus after both have been transformed by intense heat.

Contents

Why the scrolls are difficult to read

In AD 79, the eruption of Vesuvius destroyed Herculaneum, in what is now Italy. Hot gas, ash and pumice burned objects in the town, while later waves of volcanic mud buried the remains. More than 1,000 papyrus scrolls were carbonized and preserved in that state.

The collection is described as the only known complete library from antiquity. Attempts to physically unroll some of the scrolls after their discovery in 1752 caused several to crumble into ash. That history makes non-invasive reading especially important: handling the scrolls can destroy the very material researchers are trying to study.

X-ray computed tomography, or CT, has already allowed researchers to build three-dimensional models of some scrolls and digitally separate their layers. Machine-learning methods can then assist with virtually unrolling the scans. The major imaging difficulty is that conventional CT methods examine differences in carbon-based material, while both the papyrus and much of the ink contain carbon.

How the lead-detection method works

Douglas Seiler and colleagues tested whether lead could provide a more distinct signal than carbon. They sourced papyrus and reed pens from Egypt and used traditional lampblack ink from Japan. The researchers added different concentrations of lead to the ink, wrote on the papyrus, rolled the sheets and heated them in a high-temperature furnace to reproduce the carbonization of the ancient scrolls.

The resulting objects were scanned at the US National Institute of Standards and Technology using its Neutron and X-ray Tomography system. The scans produced three-dimensional renderings assembled from thousands of individual slices.

The team then virtually unrolled the model scrolls with a customised version of software originally developed to study thin-film coils inside lithium-ion batteries. In that earlier application, the software was used to understand performance loss in batteries. Here, it was adapted to follow the tightly wound layers of a damaged papyrus scroll and expose the locations of the writing.

Because lead can be distinguished from the carbon-rich papyrus more readily than carbon-based ink can, its presence gives the imaging system a clearer target. The researchers reported that this made the writing in their burned test scrolls detectable without opening them.

What the experiment could enable

The approach could support efforts to read the Herculaneum scrolls that remain too fragile to handle. Earlier virtual-unrolling work has already used CT scans and machine learning to identify writing in some of the scrolls, including a Greek work recovered through the Vesuvius Challenge. Improving the visibility of ink could make the digital-unwrapping process more effective and help researchers examine more of the collection.

The laboratory design is important to interpreting the result. The team recreated papyrus, ink, rolling and heating conditions; it did not report applying this lead-detection method to a newly deciphered passage from an original Herculaneum scroll. The next practical challenge is determining how well the signal survives in the ancient material and how reliably the resulting virtual surfaces can be converted into readable text.

For now, the study adds a chemical-imaging strategy to the existing combination of tomography and computational reconstruction. That could give researchers another way to separate ancient writing from the carbonized pages surrounding it, while preserving the unopened scrolls themselves.

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