This latest study builds on work over the past decade or so to investigate the invention and history of ink in ancient Egypt, Greece, and Rome. “Ink is history, in the sense that ink has been used to inscribe a vast number of scripts and languages on various media over the course of more than 5,000 years,” the authors wrote, with the earliest such examples dating back to Egypt, circa 3200 BCE. During this period, black ink was used to write the main body of a text, and red ink was used for highlighting headings, keywords, and so forth.

“By applying 21st-century, state-of-the-art technology to reveal the hidden secrets of ancient ink technology, we are contributing to the unveiling of the origin of writing practices,” said coauthor Marine Cotte, a scientist at the ESRF.

These inks were typically made from soot and ocher, mixed with some kind of binder (usually gum arabic), then suspended in animal glue, vegetable oil, or vinegar. Then the mixture would be dried and pressed into pellets so that scribes could easily carry the inks with them. When they needed to use it, they would mix the dried pellet with a bit of water, using the nib of a reed pen for the actual writing. In that sense, the colorants were more closely akin to paints, in that they would be classified as pigments rather than dyes.

Cotte, Christiansen, and their colleagues have previously studied the red, orange, and pink inks used on 11 surviving fragments from several manuscripts found in two small cellars in the so-called Tebtunis Temple Library, southwest of Cairo. That work revealed an unusual red ink based on a mixture of iron and lead compounds that had not been previously documented, although there is a reference in Pliny’s Natural History to blending red ocher and lead white to make an orange-reddish pigment. It was generally used as a flesh tone by Egyptian painters between 30 BCE to 400 AD, according to the authors, but had not been identified in ancient Egyptian papyri until their study.

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 coauthor 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.”