Moldmates Matter: Computational Tools to Enhance, Measure, Compare, and Match Historical Papers

Every sheet of premachine European paper bears the marks of three unique features of the handcrafted mold that was used to form it: the watermark, intervals between chain wires, and densities of laid wires (measured in frequency per inch/centimeter). Like a fingerprint, the internal patterns produced by the mold create a singular code. Two papers formed from the same mold and, thus, sharing the same code, are called “moldmates.” Scholars have long studied watermarks and, to a lesser extent, chain-line intervals in order to identify identical papers. Confirming moldmate status, however, has been difficult due to poor imaging. Laid-line density patterns have never been systematically recorded and studied. This article presents a protocol for applying computational programs to enhance, measure, compare, and match historical papers; the method is illustrated through case studies involving watermarked papers found in the Codex Leicester (Gates Collection) and the Codex Arundel (British Library, MS 263) by Leonardo da Vinci (1452–1519).