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.T he development of alphabetic writing is one of the crucial steps in the history of Western civilization (1). Starting from the earliest examples, the writing that Greeks imported from Phoenicia is characterized by a quite regular layout, with letters evenly written between imaginary parallel lines (2). Capital letters, initially found in Greek manuscripts, then in Latin documents, and later in all of the languages based on Roman scripts (such as most Western and Central European languages, as well as many languages from other parts of the world), are based on this bilinear characteristic (3). If ruling lines is a well-established practice for writing on parchment supports in the Middle Ages (4), it is generally recognized that they were not necessary in papyri, the fibrous structure of which has been deemed sufficient for enabling the good alignment of written lines, even if their horizontal spacing was sometimes marked by a series of vertical dots. Eric G. Turner (3) argued that some material, no longer visible, was perhaps used for ruled lines on papyri; however, this claim cannot be supported by material evidence in the present state of paleographical knowledge (3, 5).The same historical considerations apply to the chemical composition of the inks used in antiquity. Pliny the Elder carefully describes the carbon-based ink used in his time, which was obtained from smoke from wood burnt in furnaces, without any deliberate addition of metal (1). In the case of the most ancient manuscripts, and particularly the literary papyri both in Greek and Latin, it has been assumed that the ink used for writing was carbon-based, at least until the fourth to fifth centuries AD (4, 6, 7). The occasional use of metallic ink before this period has been known: it is reported to be used for writing secret messages in the second century BC (8), and Pliny remarks that papyrus soaked in tannin turns black after contact with a solution of iron salt (1). Moreover, Wagner et al. demonstrate the use of metal in inks in an ancient Egyptian papyrus (9), although none of those special inks has ever been menti...