Egyptian smiths may have wrought more than the desert kingdom's metals. X-ray microscopy studies have revealed the presence of copper in inks written on 2000-year-old papyrus scrolls. This previously unknown component was likely an unintentional addition to the compounds, and suggests that the pigments were obtained as a byproduct of ore processing.
Ancient Egyptians are perhaps best known for their pyramids and the emoji-like writing they employed, the hieroglyphs. They were, however, more advanced than you'd credit an 'ancient' people with, as evidenced by the fact that researchers are still running into surprises they left over.
One new such insight comes from a cross-disciplinary team at the University of Copenhagen, Denmark. The researchers, led by Egyptologist Thomas Christiansen, analyzed the chemical composition of inks etched on fragments of the university's Carlsberg Collection of papyri. They discovered traces of copper, a previously-undocumented compound in the pigments, suggesting they were a byproduct of sulfurous ore smelting.
The Carlsberg papyri were produced over a period of 300 years throughout ancient Egypt, and came from two primary sources. The first source was a man named Horus, a soldier stationed at a military camp in Pathyris (today's Gebelein). His personal papers, some 50 sheets of Greek and Egyptian papyri "that date to the late 2nd and early 1st century BCE," survived the destruction of the camp in 88 BCE during a period of civil war, and are now spread among several collections around the world.
The other source was the temple of Tebtunis (modern Umm el-Breigât,) the only known large-scale institutional library from ancient Egypt. An estimated 400-500 manuscripts were recovered from this site, "spanning the 1st through the early 3rd century CE, with the bulk dating to the late 1st and 2nd centuries." These sheets are especially poorly preserved and have broken down into thousands of smaller fragments over the years. It's so bad that on average, only 10% of each manuscript is likely to have been preserved, making it very difficult and time-consuming to puzzle together individual sheets. The researchers hoped that by analyzing the inks, they could help quicken this reconstruction process.
They worked with 12 fragments, all of them "of a light brown color and the inks range from deep black to light grey or brown," of approximately 0.3 mm thickness. These fragments were analyzed with advanced synchrotron radiation based X-ray microscopy equipment at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) as part of the University's CoNext project, an initiative that promotes "harvesting the full potential of the new neutron and X-ray research infrastructures close to Copenhagen University."
The authors report that despite the widespread origins of the papyri, both geographically and through time, the inks' composition "showed no significant differences." One unexpected finding, however, was that out of the 12 samples, six showed traces of copper, and a single fragment showed traces of lead. The other five were likely produced using soot or powdered charcoal as a pigment.
Signs of copper
The team further analyzed the four samples that showed the strongest response for copper and one sample written with carbon-based ink. Two of the former were Greek contracts recovered from Pathyris that date to 134 BCE and 101 BCE respectively. The other two came from Tebtunis and were dated to the 1st/2nd century CE. The fifth sample also came from Pathyris, dates to around 100 BCE, and was written in a cursive, more day-to-day Egyptian script called demotic.
Analysis of the black copper-less ink suggests it was based "on amorphous carbon obtained through the pyrolysis or macerating of botanicals," the authors report. Meanwhile, "it is likely that the soot/charcoal of copper-containing carbon inks were obtained during manufacturing processes related to the extraction of copper from sulfurous ores like chalcopyrite." They cite the production process of Egyptian blue, a copper-bearing pigment that the Egyptians made "from scrap or by-product copper obtained at temple workshops that either melted copper or produced glass and faience." However, considering the diffuse distribution of these elements and the absence of micrometric Cu-based spots, it cannot be concluded that these elements originate from the copper source; they are rather associated with the soot and the binder
"The composition of the copper-containing carbon inks showed no significant differences that could be related to time periods or geographical locations, which suggests that the ancient Egyptians used the same technology for ink production throughout Egypt from roughly 200 BC to 100 AD," says Egyptologist and first author of the study Thomas Christiansen from the University of Copenhagen.
The analysis found potassium (K) and chlorine (Cl) in the papyrus' fibers. Silicon (Si) showed complementary distribution, "as if it fills the holes left by the K-Cl based fiber structure." Sodium (Na), magnesium (Mg), aluminum (Al), phosphor (P), sulfur (S), calcium (Ca), and manganese (Mn) had a more homogenous distribution on the fragments "independently of the fibrous structure". Iron (Fe) was found throughout the fragments independently of the ink.
'Not significant' isn't the same thing as 'no difference,' however. None of these four inks were identical, the team write, and there were variations even within the same sheet. This showcases how variable ink composition could be, even for inks produced at the same location.
"This makes it impossible to produce maps of ink signatures that otherwise could have been used to date and place papyri fragments of uncertain provenance," explains Thomas Christiansen but adds:
"However, as many papyri have been handed down to us as fragments, the observation that ink used on individual manuscripts can differ from other manuscripts from the same source is good news insofar as it might facilitate the identification of fragments belonging to specific manuscripts or sections thereof."
According to the researchers, their results will also be useful for conservation purposes as detailed knowledge of the material's composition could help museums and collections make the right decisions regarding conservation and storage of papyri, thus ensuring their preservation and longevity
The paper "The nature of ancient Egyptian copper-containing carbon inks is revealed by synchrotron radiation based X-ray microscopy" has been published in the journal Nature.