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High-energy X-rays reveal the secrets of ancient Egyptian inks:

For this latest study, the team was interested in analyzing the mineral compounds of the red and black inks from the temple papyri fragments, especially the specific iron and lead compounds. They used numerous synchrotron radiation techniques to probe the chemical composition, including micro X-ray fluorescence, micro X-ray diffraction, and micro-infrared spectroscopy. They found a complex mix of lead phosphates, potassium lead sulphates, lead carboxylates, and lead chlorides.

"The iron-based compounds in the red inks are most likely ocher—a natural earth pigment—because the iron was found together with aluminium and the mineral hematite, which occur in ocher," said co-author Sine Larsen, also of the University of Copenhagen, of the results. "The lead compounds appear in both the red and black inks, but since we did not identify any of the typical lead-based pigments used to color the ink, we suggest that this particular lead compound was used by the scribes to dry the ink rather than as a pigment."

[...] The team also noted an unusual "coffee ring effect" in the red ink markings. The coffee ring effect occurs when a single liquid evaporates and the solids that had been dissolved in the liquid, like coffee grounds, form a telltale ring. It happens because the evaporation occurs faster at the edge than at the center. Any remaining liquid flows outward to the edge to fill in the gaps, dragging those solids with it. In this case, the red ocher pigment is present in coarse particles, which stayed in place while the more finely ground soluble lead compounds diffused into the papyrus cells to create a ring effect, making it appear (at the micrometer scale) as if the letters had been outlined.

"The advanced synchrotron-based microanalyses have provided us with invaluable knowledge of the preparation and composition of red and black inks in ancient Egypt and Rome 2,000 years ago," said Christiansen.

Journal Reference:
Thomas Christiansen, Marine Cotte, Wout de Nolf, et al. Insights into the composition of ancient Egyptian red and black inks on papyri achieved by synchrotron-based microanalyses [open], Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2004534117)

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