Knowledge in Surface Details: Reflectance Transformation Imaging for Studying and Preserving Medieval Manuscripts

Conventional photography does not capture surface details well. Generally, photographers attempt to minimize variations, like shadows, which could reveal such details. When variations occur, photographers tend to mitigate them through post-processing techniques—like flat-field correction. However, surface details hold invaluable information. In the case of medieval manuscripts, many contain dry-point glosses. These glosses are notoriously difficult to see. By design, they are made to go unnoticed, etched with a stylus but no ink. To view them requires an acute angle to the surface of the page and aid from a raking light—conditions antithetical to conventional photography. Developed to capture and highlight surface detail, Reflectance Transformation Imaging (RTI) generates a composite image from a series of photographs taken with varied directional lighting, revealing difficult to see features like dry-point glosses and other surface details.

In my talk, I will discuss uses of RTI to capture surface details in the 8th-century St Chad Gospels. These details include dry-point glosses and the state of the manuscript's pigments. RTI has generally been used to capture the likes of carved stones, cuneiform tablets, brick stamps, wall paintings, and small artifacts, like coins. As I will demonstrate, RTI has great benefits for capturing, studying, and preserving manuscripts. For instance, scholars studying dry-point glosses regularly report uncertainty as to a gloss' content. The composite images generated by RTI eliminate much of this uncertainty. Furthermore, RTI reveals vital information about the state of a manuscript's pigments, especially a manuscript such as the St Chad Gospels in which its artists layered pigments. When compared with a series of conventional photographs taken over time, visual information from RTI provides benefit for mapping the aging process of a manuscript.