A cache of papyrus scrolls damaged by the eruption of Mount Vesuvius may not be destined to keep their secrets forever.
The 1,800 scrolls were found some 260 years ago buried in the Villa dei Papiri in the ancient Roman city of Herculaneum, which was destroyed alongside Pompeii in the catastrophic eruption. Though the scrolls survived, volcanic gases carbonised the papyrus, making them extremely brittle. Attempts to unroll the scrolls would cause them to crumble.
From 1999, researchers were able to start reading and digitising most of the scrolls without having to unroll them using multispectral imaging, a technique that allowed researchers to differentiate the ink from the papyrus using reflected electromagnetic frequencies. Using this method, 1,600 of the scrolls were digitised.
For some of the scrolls, this technique proved ineffective as the scrolls were too brittle and dense. Using X-ray micro-computed tomography, a team of researchers at the University of Kentucky were able to ascertain in 2009 the physical properties inside two of these scrolls, discovering that they were very tightly furled. They were also too charred to find out more -- there was too little difference between the carbonised papyrus and the charcoal-based ink for multispectral imaging to be effective.
The only hope was to wait until imaging techniques were sophisticated enough to differentiate the ink from the papyrus -- which is exactly what has now occurred. Dr Vito Mocella and colleagues of the Institute of Microelectronics and Microsystems of the National Council of Research in Naples, Italy, have not only isolated writing, they have figured out the letters and -- they believe -- the individual handwriting.
The technique they have used is X-ray phase-contrast tomography. This monitors the changes in the phase -- that is, the speed -- of an X-ray beam as it passes through material. When the radiation beam passed through the ink, the change was faint, but detectable.
The team subjected two scrolls to this technique -- one unrolled and one rolled up. The unrolled scroll, called P.Herc.Paris. 1, was used as a "control" -- that is, to determine, before attempting the technique on the second scroll, known as P.Herc.Paris. 4, that the XPCT was effective at differentiating between ink and papyrus.
PHerc.Paris. 1 was partially unrolled in 1986, a process that broke the scroll. The piece X-rayed had several layers, and the team was able to successfully read two words on a hidden layer -- PIPTOIE and EIPOI, meaning "would fall" and "would say" respectively.
On the rolled-up scroll, P.Herc.Paris. 4, they managed to make out a variety of letters -- APN, HEY and KI. These are probably just fragments of words, and little can be ascertained about the contents of the scroll. However, the handwriting itself bore a strong similarity to another Herculaneum scroll, PHerc. 1471, penned by Epicurean philosopher Philodemus.
The team believes this is a good first step into one day reading these scrolls more fully, since the experiment was intended merely as a proof of concept, and can be fine-tuned -- perhaps using the more sensitive grating interferometry imaging technique rather than XPCT.
"The impact of our discovery that XPCT can read writing inside carbonised papyrus rolls reaches far beyond the study of one particular Herculaneum papyrus. It holds out the promise that many philosophical works from the library of the Villa dei Papiri, the contents of which have so far remained unknown, may in future be deciphered without damaging the papyrus in any way," the team concluded.
"This pioneering research opens up new prospects not only for the many papyri still unopened, but also for others that have not yet been discovered, perhaps including a second library of Latin papyri at a lower, as-yet unexcavated level of the Villa."