Physicists discover a text hidden in virgin Egyptian papyri

A team of German scientists used a combination of advanced physics techniques to virtually "unfold" an ancient Egyptian papyrus, which is part of a vast collection kept at the Egyptian Museum in Berlin. Their analysis revealed that an apparently blank spot on papyrus actually contained written characters in what had become "invisible ink" after centuries of exposure to light.

Most of the collection 's papyrus were unearthed around 1906 by an archaeologist named Otto Rubensohn, on Elephantine Island, near the city of Aswan. They accumulated dust during the decades that followed and, because of their fragility, more than 80% of the text is not encrypted. "Today, much of this papyrus has aged considerably, so valuable texts can easily crumble if we try to unroll them or unroll them," said co-author Heinz -Eberhard Mahnke from Helmholtz-Zentrum Berlin and Freie Universität Berlin. This makes the non-invasive imaging methods essential to the project.

In 2016, an international team of scientists developed a method to "unroll virtually" a severely damaged old parchment discovered on the west bank of the Dead Sea, revealing the first verses of the book of Leviticus. The so-called scroll In Gedi was recovered in the ark of an old synagogue destroyed by fire around 600 AD. To the naked eye, it looked like a small mass of charcoal, so fragile that there was no sure way to analyze the contents. The team's approach combined digital scanning and micro-computed tomography, a non-invasive technique often used for cancer imaging, with segmentation to create pages digitally, complemented by texturing techniques and flattening. They then developed a software (volume mapping) to scroll virtually the parchment.

"Much of this papyrus has aged considerably, so valuable texts can easily crumble if we try to unroll them or unroll them."

The artifacts analyzed by the German team were made of a different material. A different approach was therefore needed to discover the hidden text. "Gedi parchment is a parchment," said Mahnke. "We are dealing with a papyrus." The papyrus is produced from the plant's stems in two layers, perpendicular to the fiber direction, he noted. The varying thickness of the basic writing support can make it more difficult to identify the script. In addition, the papyri that he and his colleagues studied were folded along orthogonal lines rather than rolled, so that objects occupy as little space as possible. "Mathematically, a parchment is a roll, topologically identical, that it's a well-rolled or strongly deformed cylinder," Mahnke said. A folded papyrus does not have this benefit.

Thus, Mahnke and his colleagues used the synchrotron radiation source of the BESSY II facility of Berlin (German electron storage company for synchrotron radiation) in Berlin for their experiments, relying on work done earlier this year to demonstrate proof of principle on a simulated sample. Synchrotron radiation differs from conventional X-rays in that it is a very high-intensity thin X-ray beam generated in a particle accelerator. The electrons are drawn in a linear accelerator (linac), accelerated in a small synchrotron and injected into a storage ring, where they zoom at a speed close to that of light. A series of magnets bend and focus the electrons and, in doing so, emit X-rays which can then be focused on beamlines.

Secrets revealed

This makes it ideal for noninvasive imaging, because in general, the shorter the wavelength used (and the higher the light energy is), the more details can be viewed and viewed. / or analyzed. And the technique can be used to image fragile archaeological artifacts without damaging them. Shine this high-energy X-ray beam on a fragile papyrus and the photons excite the atoms, emitting X-echoes in response. These echoes will fluoresce in different ways depending on the atoms present in the sample.

According to Mahnke, it was common for Egyptian scholars to use a black ink made of charred wood or bone chips, in other words, carbon-based inks. But they would also use colored inks containing traces of metallic elements such as iron, copper, mercury or lead. The X-ray fluorescence produced during the sample imaging must therefore indicate if these metallic elements are present.

For example, the German team found traces of lead in the blank papyrus plate and was able to discern fuzzy and fuzzy characters. Infrared spectrometry identified the ink as being a colorless lead carboxylate. However, "we think the characters may have been originally written in bright minium (red lead) or perhaps in black galena like coal," Mahnke said. Over the centuries, these inks would have slowly turned into invisible lead carboxylate, leaving a seemingly empty space on the papyrus.

In order to improve the luminosity and to obtain a better contrast between the papyrus and the characters, the team combined the absorption x-ray and tomography to better illuminate the sample. This gave them a clearer picture of the characters, although no one has yet been able to translate them. The analysis of another papyrus revealed the word Coptic meaning "Lord".

The best part: German researchers have been able to virtually open fragile papyri without ever touching them. It should now be possible to use these techniques to study the remaining papyri collections of Elephantine Island. "The most important challenge is to reveal a text written in carbon ink, which shows virtually no contrast in absorption tomography," said Mahnke. "We need to find subtle differences to distinguish the organic (carbon-based) material from the ink (also carbon-based) [that is] good enough for a contrast. "

DO I: Journal of Cultural Heritage, 2019. 10.1016 / j.culher.2019.07.007 (About DOIs).