Lead in ancient ink makes burned Herculaneum scrolls 'light up' in X-ray scans

To solve a nearly 2,000-year-old problem, Douglas Seiler first had to create one. He sourced papyrus and reed pens from Egypt and traditional lampblack ink from Japan, paid high school students to inscribe the papyrus with lines from Star Wars, the Bible, and a quote from the 1960s TV show The Outer Limits — then rolled it up, sealed it in a container, and burned it to a crisp in a high-temperature furnace.

The destruction was the point. Seiler, an affiliate of Berkeley SETI, was replicating what Mount Vesuvius did to more than a thousand papyrus scrolls in Herculaneum in 79 C.E. — turning an entire library into fragile, carbonized husks that crumble at a touch. His question: could X-rays read what no human hand can safely open?

The answer, published September 16 in the journal PLOS ONE, is yes — but only if the ink contains lead. Even minuscule amounts of the metal absorb up to 25 times more X-rays than the surrounding burned papyrus, causing inked letters to stand out dramatically in X-ray CT scans. A software algorithm, adapted from lithium-ion battery analysis, can then virtually unroll the scans to expose the hidden text.

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. They're having problems reading a lot of them because of the low contrast of carbon ink on carbon paper. We're relatively certain that if they start searching for lead, or they let us search for lead, it will help this whole process. This is the Holy Grail.— Douglas Seiler, Berkeley SETI affiliate

The Herculaneum collection — roughly 1,800 scrolls and scroll fragments now held in Italy, France, and England — is the only known intact library to survive from antiquity. When the scrolls were discovered in 1752, early attempts to physically unroll them mostly produced heaps of ash. Italian authorities eventually halted the practice. Of those that were successfully opened, every single one contained texts previously unknown to scholars, many of them works by Philodemus, an Epicurean philosopher who lived in Herculaneum about a century before the eruption.

To date, only a small number of the charred scrolls have been virtually unrolled and read using modern imaging — and none of them were first tested for lead in their ink. No systematic search for lead-based ink across the collection has been carried out, though at least one previous researcher detected lead in ink from a fragment left over from the early physical-unrolling attempts, according to the Berkeley team.

The researchers also demonstrated that a relatively inexpensive handheld X-ray fluorescence scanner can quickly detect whether a scroll's ink contains lead — providing a practical screening tool to identify the most promising candidates for full X-ray CT imaging before committing to the more intensive process.

The lead-ink finding draws support from work already underway at Berkeley. Leah Packard-Grams, an archaeology graduate student and papyrologist who consulted on the project, has been studying ink chemistry on the Tebtunis Papyri — fragments dating from 300 B.C.E. to 300 C.E., excavated for UC Berkeley 126 years ago at the site of the ancient Egyptian city of Tebtunis. Using a handheld X-ray fluorescence scanner, she confirmed that some of those scrolls — generally those written after the first century C.E. — contain ink with lead and/or copper. That finding, she said, bodes well for finding lead in at least some of the Herculaneum scrolls.

If we know that the Herculaneum papyri have lead in them — some of them do, some of them don't — then when they take the CT scan, they can scan it with a sensitivity for the element lead and we can see where the ink is. As you unroll it, you can map the letters a lot more clearly.— Leah Packard-Grams, Berkeley archaeology graduate student and papyrologist

Packard-Grams also has a longer-term hope: that ink chemistry — including any metals, whether accidentally present or deliberately added — could eventually serve as a kind of fingerprint to identify the author of a specific ancient text. Traditional ink was made from soot, water, and a binder such as gum Arabic; any metallic variation from that baseline could carry identifying information.

The value in this project is practically unquantifiable. The stakes are the largest in the history of Greek literature.— Leah Packard-Grams, Berkeley archaeology graduate student and papyrologist

For Packard-Grams, the stakes are personal as well as scholarly. She currently translates Greek and Egyptian writing at UC Berkeley's Center for the Tebtunis Papyri in the Bancroft Library, including fragments written by a man named Dionysios — a school teacher and scribe-for-hire whose surviving notes record the costs of food he bought for his children along the canal.

This is what drew me to papyrology — that I could read the words of ancient people not through a library book or through a Renaissance copy but actually sit down and know that someone wrote this letter to whomever, his father or something. It's autograph history — not just from a book, but from what they were actually writing.— Leah Packard-Grams, Berkeley archaeology graduate student and papyrologist

Seiler frames the broader loss in stark terms. Most ancient writing is gone — surviving only in copies made by medieval scribes, or on papyri preserved by accident in Egypt's dry climate. The Herculaneum scrolls are different: originals, frozen in time, from Roman intellectual circles. The eruption that destroyed them also, paradoxically, kept them from the slow decay that erased nearly everything else.

Almost everything from antiquity has been destroyed. 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.— Douglas Seiler, Berkeley SETI affiliate

The new findings sit alongside ongoing efforts under the Vesuvius Challenge, a broader initiative using artificial intelligence and imaging to decipher the original Herculaneum scrolls. The lead-ink method, developed with collaborators including researchers at the National Institute of Standards and Technology (NIST), offers a complementary and potentially faster first step: screen for lead, then scan.

Why it matters — If lead-based ink is found in significant portions of the Herculaneum collection, a cheap handheld scanner combined with X-ray CT could unlock hundreds of ancient texts — including works of philosophy, science, and literature that exist nowhere else on Earth.

Reported by sciencedaily.com, sciencealert.com, news.berkeley.edu, ancientist.com