The black ink used by Egyptian scribes to write on 2,000-year-old papyri fragments also contained copper, an element previously not identified in ancient ink.
Papyri is a material similar to thick paper that was used in ancient times as writing surface. It was made from the pith of the papyrus plant, Cyperus papyrus, a wetland sedge.
Until recently, it was assumed that the ink used for writing was primarily carbon-based at least until the fourth and fifth centuries AD.
However, the findings showed that the Egyptian scribes began mixing copper into their carbon-based inks much earlier than previously thought.
Further, the particles found in the inks indicated that they were by-products of the extraction of copper from sulphurous ores.
"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," said lead author Thomas Christiansen, an Egyptologist at the University of Copenhagen in Denmark.
For the study, published in the journal Scientific Reports, the team conducted analyses of 2,000-year-old papyri fragments with X-ray microscopy.
The practice was apparently widespread, as copper was found in a variety of papyri fragments, hailing from different geographical regions and produced over a period of 300 years.
"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 in so far as it might facilitate the identification of fragments belonging to specific manuscripts or sections thereof," Christiansen said.
Knowledge of the composition of inks could help museums and collections make the right decisions regarding conservation and storage of papyri, the researchers said.