Metallic ink has been found in two papyrus fragments, says new research into the famous scrolls carbonized nearly 2,000 years ago by Mount Vesuvius' eruption.
The finding proves that metal-bearing ink was used several centuries earlier than previously believed.
The research, published in the journal PNAS, relied on synchrotron X-ray based techniques at the European Synchrotron Radiation Facility in Grenoble, France, to reveal a high concentration of lead in the ancient ink.
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"We are reasonably certain that lead was intentionally used. It doesn't come from contamination of water from Roman aqueducts or from a bronze container," Vito Mocella, a physicist from the National Research Council's Institute for Microelectronics and Microsystems (CNR-IMM) in Naples, told Discovery News.
Along with Emmanuel Brun at the Grenoble Institute of Neurosciences, Daniel Delattre, papyrologist from the CNRS-IRHT- Institut de Recherche et d'Histoire des Textes, and colleagues, Mocella examined two multilayered fragments that were handed to Napoleon Bonaparte as a gift in 1802 and now belong to the collection of the Institut de France.
"We do not know their exact dating. Most of the papyri in the villa date from the first century B.C., though the oldest one goes back to the 3rd century B.C.," Mocella said.
Until now it was assumed the ink used for the most ancient manuscripts, particularly the literary papyri both in Greek and Latin, was carbon-based -– obtained from smoke residues of wood burnt in furnaces.
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Researchers estimate that metal was only introduced to ink by the fourth century A.D.
From around 420 A.D., a metallic iron-gall mixture was adopted for parchments as this support required a more adherent ink. Thereafter, metallic inks became the standard for parchments in late Antiquity and for most of the Middle Ages.
The scroll fragments used by the researchers were excavated more than 260 years ago from the Villa of the Papyri in Herculaneum, a magnificent seafront estate perhaps owned by Lucius Calpurnius Piso, Julius Caesar's father-in-law.
Carefully stored in shelves covering the walls, the scrolls made one of the finest libraries of antiquity.
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They were reduced to lumps of coal by the 750-degree Fahrenheit cloud that enveloped the ancient Roman city of Herculaneum during the Mount Vesuvius eruption in 79 A.D. Ironically the incineration preserved the scrolls forever (Herculaneum's seaside air would have destroyed them otherwise) and they are now stored at the National Library of Naples.
They make up the only library known to have survived the ancient world. The carbonized scrolls are thought to hold Aristotle's lost 30 dialogues, philosophical work by Epicurus, erotic poems by Philodemus, Virgilius, scientific work by Archimedes and lesbian poetry by Sappho.
Out of the 1,785 scrolls discovered during the 18th century excavation, only 585 had been completely unrolled using a 18th century mechanical method, while 209 have been partly unrolled.
About 400 have never been unrolled and 450 are so difficult to read that their text remains unknown.
Any attempt using non invasive procedures to read the scroll, including multi-spectral technology, had proven ineffective -– until last year.
In January 2015, Mocella and colleagues used a powerful X-ray procedure to decipher words in the scrolls. Indeed, they reconstructed an almost complete Greek alphabet from inside badly damaged and rolled papyri.
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The latest work focused on the chemical composition of the ink and papyrus texture in the fragments.
It emerged that a lead-bearing material was intentionally introduced in the ink production process.
Moreover, the analysis revealed the scribes used straight and thick horizontal papyrus fibers to guide the writing of letters in straight lines, avoiding any additional material to trace ruled lines.
The finding "deeply modifies our knowledge of Greek and Latin writing in antiquity," the researchers wrote.
They speculate that lead could have been added for its property to speed up the process of ink drying.
The new finding promises to open new paths of exploration into the Herculaneum scrolls.
"It will allow us to optimize the next experiments on the reading of the invisible text within the scrolls," main author Brun said.
The researchers believe the discovery may also have some effect on other archaeological studies.
For example, black powders found in Pompeii were discarded as remainders of ink as they contained metals such as lead.
The researchers agree that more extensive research using other fragments from Herculaneum is needed. Further experiments may also help reveal the true recipe of the ancient ink.