Advanced imaging technology has been used for over two decades to read hidden texts within parchment manuscripts. The early pioneering work in the field was carried out by an international team of data scientists, imaging experts, and manuscript scholars, who came together to image the now famous Archimedes Palimpsest, found to contain lost mathematical treatises of ancient Greek mathematician Archimedes. More recently, imaging was carried out on the Syriac Galen Palimpsest, that revealed the scrubbed off text of Sergius of Resh 'Ayno's Syriac translation of ancient physician Galen's Greek pharmacological treatise, "On Simple Drugs." Each project enhances the application of advanced imaging for manuscript studies and the HMML Palimpsest Project builds on these earlier imaging experiments, furthering technology in the field.
Narrowband multispectral imaging is often the first technology applied to imaging a palimpsest. This non-destructive technique projects multiple narrow wavelengths of light onto the sheet - ranging from ultraviolet through the visible and infrared - visually amplifying compounds found in inks, pigments, and residue. The resulting data, which captures this response, must be processed to produce images and adjusted to enhance specific areas of text. For texts that are sitting well below the surface of the parchment or are obscured by other elements, XRF imaging may be required to image them. This was the case with the HMML Palimpsest, which has a coating of calcium on the surface that made MSI imaging difficult. Early Syriac manuscripts often have calcium present, and these experiments will improve the knowledge of how to image palimpsests from this tradition.
Multispectral image of the HMML Palimpsest, with areas of Syriac underwriting circled (image: MB Toth)
X-ray Fluorescence Imaging
X-ray fluorescence (XRF) imaging provides non-destructive elemental analysis, using a high-powered x-ray source to cause elements in an object to emit x-ray energy. This response is captured and mapped to identify elements found embedded within the sheet, such as the iron, zinc, and copper that can be found in iron-gall ink. With XRF, the metals in inks can be isolated from the calcium in the sheet, and this differentiation produces more detailed data and imagery.
The Synchrotron Radiation Lightsource (SSRL) at Stanford’s SLAC National Accelerator Laboratory is one of a few places in the world where this imaging is performed. Similar to the MSI process, raw data must be processed to produce images. For the HMML Palimpsest, the research team will use SMAK processing software (an acronym that stands for SSRL data scientist Sam Webb's Microprobe Analysis Kit). The software puts data manipulation into the hands of scholars, so they can process images themselves, enhance, reduce, and refine certain elements for better analysis of the hidden texts.
Some of the XRF team at SLAC. Left to right: Sam Webb (SLAC/SSRL), Michael Penn (Stanford), Nicholas P. Edwards (SLAC/SSRL), Wayne Torborg and David Calabro (HMML), and Mike B. Toth (RB Toth Associates) (image: SLAC)
SLAC/ SSRL team member, Uwe Bergmann, adjusting the XRF lightsource before imaging the HMML Palimpsest
Initial processing of XRF data, showing columns of text (image: MB Toth)