A biological reading of a palimpsest

n the Middle Ages, texts were recorded and preserved on parchment, an animal-derived material. When this resource was scarce, older manuscripts were sometimes recycled to write new manuscripts. In the process, the ancient text was erased, creating what is known as a palimpsest. Here, we explore the potential of peptide mass fingerprinting (PMF), widely applied to identify species, to help reconnect the dispersed leaves of a manuscript and reveal differences in parchment manufacturing. In combination with visual methods, we analyzed a whole palimpsest, the codex AM 795 4to from the Arnamagnæan Collection (Copenhagen, Denmark). We find that both sheep and goat skins were used in this manuscript, and that parchment differed in quality. Notably, the PMF analysis distinguished five groups of folios which match the visual groupings. We conclude that this detailed interrogation of a single mass spectrum can be a promising tool to understand how palimpsest manuscripts were constructed