Earlier analysis by the team of an extremely fragile carbonized papyrus scroll from Herculaneum revealed the "huge complexity" within, where the convolutions of the scroll were exposed to tremendous stresses. Image credit: Mocella et al. in Nature Communications

The eruption of Mount Vesuvius in 79 CE preserved the texts that lined the library walls of a sprawling villa at Herculaneum, a Roman town neighboring Pompeii. But the scrolls were carbonized in the eruption, and most of them are too fragile today to unroll mechanically. (The few texts that have been opened and translated give hope that the collection might contain lost works of the Greek philosopher Epicurus.)

Since the library was discovered in the ruins of Herculaneum in the 18th century, antiquarians and researchers have been trying to figure out ways to unroll and read these dried-out, brittle texts. Recently, a team of European scientists has been attempting to reveal hidden script using non-invasive x-ray scanning. Last year, they reported success in deciphering some words. This week, in the journal Proceedings of the National Academy of Sciences, the researchers announced another discovery: They detected traces of lead in the ink on two of the scroll fragments.

It was generally believed that there was no metal in Greco-Roman inks. One authority on ancient writing techniques, the Roman author Pliny the Elder—who died from breathing in the toxic gases from the Vesuvius eruption—described how carbon-based ink was obtained from smoke from wood burned in furnaces in his Natural History in the mid 1st century CE. The common belief among ancient historians was that the addition of metal to ink was a 4th–5th century CE innovation.

But this new discovery could push back the date of metal-laden ink by three centuries.

Papyrus is an absorbent writing medium, and lead was probably added to ink to quicken the drying process, Vito Mocella, of Italy’s National Research Council in Naples, told mental_floss.

“If we want to read these papyri, we should know the ink composition,” Mocella said.

Knowing the makeup of the ink could affect the approach Mocella and his colleagues use to scan the scrolls. With most x-ray scanning techniques, it would be tough to separate black charcoal ink from carbonized papyrus because they have a similar chemical composition. But metal absorbs x-ray radiation differently than carbon-based material. (It’s similar to how dense bone absorbs radiation differently than soft tissue, which is why medical x-rays produce images with such a clear contrast.)

For this study, Mocella and his colleagues only analyzed two fragments from Institut de France’s collection in Paris. But there are more than 1800 scrolls that were discovered in Herculaneum's Villa of the Papyri, and the scientists say they need to conduct more research to find out how prevalent lead ink is in the collection.