Ink containing lead shows up sharply on X-ray scans even after papyrus has been burned to carbon. Researchers proved it by charring their own replica scrolls in a furnace, and they describe the results in PLOS ONE.
The target is the library of the Villa of the Papyri in Herculaneum. When Vesuvius buried the town in A.D. 79, more than 1,800 scrolls and fragments were carbonized. Many remain unread, and several contain works by the philosopher Philodemus.
"The stakes are the largest in the history of Greek literature," says Leah Packard-Grams, a papyrologist and archaeology graduate student at UC Berkeley and a co-author.
Star Wars on papyrus
Douglas Seiler, an affiliate of the SETI group at Berkeley, made the replicas from real Egyptian papyrus. He used a reed pen and Japanese soot ink mixed with a measured amount of lead nitrate. High school students wrote passages from Star Wars, the Bible and The Outer Limits on them.
Seiler then charred the scrolls inside a steel container with very little oxygen, in a furnace.
Letters that glow
Physicist Jake LaManna of NIST imaged the charred replicas with 3D X-ray tomography. Lead absorbs up to 25 times more X-rays than charred papyrus, so the ink stands out.
"If you look at the images, the letters light up like a Christmas tree," Seiler says.
A handheld X-ray fluorescence scanner also detected lead at concentrations as low as 25 micrograms per square centimeter.
Picking the right scrolls
The authors present the method as a new route to identifying which Herculaneum scrolls can be read. Seiler's advice is to look specifically for scrolls with lead in the ink.
The team also includes researchers from University College London and the Rutherford Appleton Laboratory in the UK.
