METHODS OF RECOVERY have not always been kind to manuscripts. Concealing knowledge, damaged pages have long tantalized with traces of effaced script. To entice them to give up their secrets, reagents were applied, a practice which began at least in the seventeenth century but was more rigorously pursued in the nineteenth century. The results, however, were disastrous. These chemicals, such as gallic acid and ammonium sulphide, were theorized to revitalize inks. Instead, they did so only temporarily, before turning a page into something less than its previous self: regularly a brown slur (Web Fig. 1.1). Relying on the best knowledge of their day, such attempts remain a cautionary tale about the complex chemistry and fragility of the seemingly simple and common medieval materials of ink, pigment, and parchment.

Creating a theoretical frame for digital methods, early photography provided a means to recover damaged content through noninvasive techniques. It marked a critical turn from chemistry to physics, that is, recovery based on the properties of light. Early experiments generated new methods, such as using orange lighting to increase contrast and coloured filters to reduce “the obscuring effects of stains.” More complex methods demonstrated further possibilities. For example, in the early twentieth century, Pringsheim and Gradeviss devised a method for recovering erased text from palimpsests. This method required two film negatives: the first focused as sharply as possible on the erased script; the second focused equally on the two. To make the erased script more pronounced, Pringsheim and Gradeviss made a glass positive of the second negative (equal focus) and aligned and overlaid it with the negative focused on the erased script. When examined under a light, the glass positive helped to neutralize the later writing, making traces of the erased script stand out. Such early techniques exemplify the overarching goal for recovery through noninvasive photographic methods: capitalize on properties of light to increase contrast, revealing that which has been lost to the unaided eye.