"Writing on paper is essential to civilization, as Pliny the Elder remarks in his Natural History, when he describes the various types of papyri, the method of manufacturing them, and all that concerns writing materials in the mid-first century AD. For this reason, a rigorous scientific study of writing is of fundamental importance for the historical understanding of ancient societies. We show that metallic ink was used several centuries earlier than previously thought. In particular, we found strong evidence that lead was intentionally used in the ink of Herculaneum papyri and discuss the possible existence of ruled lines traced on the papyrus texture. In addition, the metallic concentrations found in these fragments deliver important information in view of optimizing future computed tomography (CT) experiments on still-unrolled Herculaneum scrolls to improve the readability of texts in the only surviving ancient Greco-Roman library."
"The common belief has been that no metal is present in Greco-Roman inks. In this work, we show that lead is present in the ink of two Herculaneum papyrus fragments. The concentration found is very high and not to be explained merely by contamination. The metal found in these fragments deeply modifies our knowledge of Greek and Latin writing in antiquity. Moreover, these concentration values allow the optimization of future computed tomography experiments on still-unrolled Herculaneum scrolls to enable the recovery of texts in the only surviving ancient Greco-Roman library. The possibility of using additional material to trace down ruled lines guiding the scribes' writing along straight lines is also addressed. We demonstrate that no additional material was used for this goal."
See also an article in Popular Archaeology.