Researchers burned their own papyrus scrolls to discover how to read those carbonized nearly 2,000 years ago by Mount Vesuvius.
In 79 CE, the eruption of Mount Vesuvius buried Herculaneum, near present-day Naples. More than a thousand scrolls from a library were found there centuries later. The heat carbonized them without reducing all of them to ash. However, they are so fragile that unrolling them by hand could destroy them.
A modern papyrus scroll before and after carbonization in an almost oxygen-free chamber.
Credit: Douglas Seiler / UC Berkeley
One solution is to scan their interiors with X-rays and then digitally reconstruct the rolled-up sheets. But one problem remains: many ancient inks consist primarily of carbon, sometimes with a small concentration of lead. Carbonized papyrus also contains a great deal of carbon, making the letters very difficult to distinguish from their support.
Douglas Seiler and his colleagues therefore made modern scrolls whose contents they knew exactly. They wrote on papyrus with several inks containing different amounts of lead. The scrolls were then heated in an oven to produce a carbonized material similar to that of the ancient documents.
Lead significantly changes the situation. Using a technique called X-ray fluorescence, the researchers were able to detect this element after carbonization, even when it was present in small amounts. The device measures the characteristic signals emitted by elements when they receive X-rays.
The team then produced three-dimensional X-ray images. Software virtually reconstructed the layers of the scroll without physically opening it. Some of the words written before carbonization could thus be read again. Above all, the experiment confirms that the presence of lead in the ink greatly increases the contrast with the burned papyrus.
This discovery could be useful even before lengthy digital-reading efforts begin. A portable X-ray fluorescence device is enough to search for lead without unrolling the papyri. Researchers could therefore examine a collection and prioritize the scrolls whose ink offers the best chance of appearing in the scans.
Not all of the Herculaneum scrolls will become readable as a result. Inks composed solely of carbon remain much more difficult to detect.
The fake scrolls also provide another tool: their original text is known. Researchers can directly compare what was written with what their software recovers after carbonization. These data can be used to improve and test virtual-unrolling methods before applying them to the precious ancient papyri.