Some Herculaneum Scrolls Were Written in Ink Laced With Lead. Berkeley and NIST Scientists Baked Fake Scrolls in a Furnace to Prove X-Rays Can Spot the Metal, and Say It Could Finally Sort the Readable Ones From the Hopeless.

The only intact library to survive from the ancient world is a stack of charcoal. When Mount Vesuvius erupted in 79 CE, it buried the seaside town of Herculaneum under 20 to 21 meters of volcanic rock and ash, and the heat carbonized the roughly 1,800 papyrus scrolls in a villa believed to have belonged to Julius Caesar's father-in-law. The scrolls survived, but as brittle black cylinders that crumble when touched. A study published Tuesday in PLOS One proposes a way to decide, before anyone tries, which of the hundreds of unopened scrolls can actually be read: look for lead.

The problem has always been contrast. Modern efforts to read the scrolls, most famously the Vesuvius Challenge that produced the first legible words from an unopened scroll in 2023, use X-ray computed tomography to image the rolled-up layers and machine learning to virtually unroll them and pick out the ink. But the ink the Romans used was carbon black, essentially soot in water, and the papyrus it was written on is now carbon too. To an X-ray, the letters and the page are nearly the same material, and the algorithms are hunting for subtle differences in texture and density rather than a clear chemical signal. Some scrolls have yielded text; many have not.

Earlier chemical analyses of scroll fragments, however, found that some of the Herculaneum ink contains lead, either as a deliberate additive or a contaminant from the bronze inkwells and lead water pipes of a Roman household. Lead is a heavy element that X-rays cannot miss. Douglas Seiler, an affiliate of the University of California, Berkeley, Jacob LaManna of the National Institute of Standards and Technology, David Kreimer of Berkeley and their colleagues set out to test whether that difference could be exploited systematically.

They could not experiment on the real scrolls, so they made their own. The team wrote on fresh papyrus with inks containing a range of lead concentrations, rolled the sheets into scrolls, and cooked them in a high-temperature furnace until they carbonized into tightly packed, wavy black cylinders that closely mimic the originals. Then they scanned them. X-ray fluorescence, which detects elements by the characteristic X-rays they emit when excited, picked up the lead at every concentration tested. X-ray tomography combined with custom unrolling software let the team read back some of the words they had written, even through the collapsed and distorted layers.

The proposal is a triage system. Scan the entire Herculaneum collection with X-ray fluorescence, a fast and non-destructive step, to identify which scrolls contain lead in their ink. Then concentrate the expensive, slow work of high-resolution tomography and virtual unrolling on those, where the ink will show up as bright metal against dark carbon. Scrolls written in pure carbon ink can wait for better methods rather than consuming beam time with little chance of success.

The furnace-made scrolls have a second use. Because the researchers know exactly what they wrote inside each one, the scans serve as ground truth for training the unrolling algorithms, which currently learn from a small number of real scrolls whose contents were only discovered after the fact. A library of synthetic scrolls with known text, varied lead content and realistic damage could sharpen those models before they are turned loose on the originals. "It's amazing what you can get electrons to do," Seiler said. The scrolls read so far have revealed lost works of the Epicurean philosopher Philodemus and, last year, a treatise on vice; the several hundred still sealed could hold anything from lost Greek plays to the missing books of Livy.