Researchers studying the carbonized scrolls of Herculaneum published a new testing method showing that lead-infused ink absorbs X-rays and makes ancient text readable under 3D CT scans without unrolling the fragile, 2,000-year-old artifacts.
Recreating Vesuvius in the Lab
When Mount Vesuvius erupted in 79 C.E., it buried Pompeii and inundated a nearby library in the Italian city of Herculaneum with hot ash, turning roughly 1,800 ancient Greek and Roman scrolls into brittle, carbonized husks. Those preserved texts represent the only known intact library from antiquity. They are also notoriously difficult to read because the carbon ink used by ancient scribes blends directly into the carbonized papyrus paper.
To test a nondestructive alternative to physical unrolling—which historically reduced most attempted scrolls to piles of black dust—Douglas Seiler built his own replica artifacts. He sourced traditional papyrus and reed pens from Egypt alongside lampblack ink from Japan, and paid high school students to write lines from the Bible, Star Wars, and a quote from the television show The Outer Limits onto the material. Seiler, an affiliate of Berkeley SETI, then rolled up the papers, placed them inside a high-temperature furnace within a nearly oxygen-free container, and baked them to a crisp.
How Lead Absorbs X-Rays
The experimental premise relied on an elemental difference: introducing minute quantities of lead into the writing ink. In a paper published on Sept. 16 in the journal PLOS ONE, Seiler and his collaborators, including a range of Berkeley experts, report that even minuscule amounts of lead in the ink make the letters readable by X-ray tomography, or X-ray CT. When researchers scanned the barbecued imitation scroll using 3D X-ray computed tomography, the lead absorbed up to 25 times the X-rays absorbed by the charred papyrus. That elemental contrast caused the written letters to stand out sharply in the resulting digital models.
“With lead in the ink, you would get a huge friggin’ signature, so you really need to be looking for scrolls with lead in them,”—Douglas Seiler, co-author
Because the initial 3D scans of a rolled scroll remain illegible from a flat perspective, the research team utilized computer algorithms to virtually unroll the digital model. This process displayed the hidden text clearly, proving that elemental signatures can guide virtual recovery techniques.
Screening Artifacts Without Damaging Them
Prior physical efforts to open the Villa of the Papyri collection began after their discovery in 1752, but Italian authorities called a halt to such efforts when unrolling mostly produced heaps of ashes. Currently, what remains of the library’s 1,800 or so scrolls and scroll fragments are housed in Italy, France and England. Only recently have scientists managed to virtually read a complete scroll, though those prior efforts did not systematically test for metallic ink. Although no one has systematically looked for leaded ink in the scrolls, at least one researcher found lead in the ink of a fragment that remained from earlier efforts to physically unroll some of them.
To check real artifacts safely, Seiler and his collaborators demonstrated that an inexpensive handheld X-ray fluorescence scanner can easily detect leaded ink in a burned scroll, providing a simple way to identify those scrolls that would be more easily deciphered using X-ray CT without causing physical harm.
If you hurt a model, it’s fine. If you hurt a 2,300-year-old ancient artifact, you’ll have a bunch of archeologists ready to jump you. As Leah
Unquantifiable Historical Stakes
Almost everything from antiquity has been destroyed,
Seiler said. “There’s very little left except papyrus that was in a dry climate or some works that were copied by scribes and transferred down. But some of the Herculaneum scrolls aren’t copies. These are books directly from the ancient world frozen in time. They’re actually from Roman intellectual circles.”
Of those physically unrolled, all have been texts unknown to scholars, many of them written by the Epicurean philosopher Philodemus, who lived in Herculaneum a century before the Vesuvius eruption.
Researchers note that while some historical fragments from earlier unrolling attempts have tested positive for lead, no one has ever thoroughly searched the Herculaneum scrolls for it. Experts hope that scanning remaining scrolls for lead signatures will help this whole process, providing a viable roadmap to recover lost ancient philosophy, science, and literature.