By Felipe Orihuela-Espina
Collaborative work led by Prof. Adam Gibson and Prof. Melissa Terras (University College London) using light to reveal information from Egyptian objects made the news recently. The project is a whole line of research that includes other investigators, institutions, and multiple funding sources, all focused on the further development and use of multispectral imaging for analyzing and digitizing heritage objects. Multispectral imaging is the combination of several monochromatic images from wavelengths in the ultraviolet, visible and near infrared range of the spectrum. Multispectral imaging usually refers to more than 3 images (to distinguish from “plain” color imaging) but not covering the whole spectrum (to distinguish from hyperspectral and broadband imaging).
What is newsworthy is the development of two closely related multispectral imaging techniques. One of these techniques employs light at 12 wavelengths from 370 to 940 nanometers to “read” papyrus cartonnage on mummy cases. Papyri containing information about life in Egypt can be found either in their original form (they were regularly used for documents), but also in a recycled form to fabricate other objects, such as mummy masks. Now these are providing an unconventional way to gather information about daily life in ancient Egypt.
Previous attempts to read the recycled papyri required carefully balancing risks so as not to destroy them. The new imaging approach exploits the fact that the ink used (known as “Egyptian blue”, and based on a pigment with carbon and iron) blue fluoresces in the near infrared range when illuminated at certain visible wavelengths. With the new multispectral imaging system, researchers were able to read the papyrus that had been used to made a mummy mask from UCL’s Petrie Museum. Multispectral imaging is the best available method to identify inks and pigments in the surface layers of cartonnage. Multimodality approaches including x-ray and terahertz methods are needed to read deeper inscriptions.
The other new technique is permitting recovery of hieroglyphs in the lids on mummy coffins. In this case, 18 distinct wavelengths and filters were combined to image the area beneath the pectoral, which was illuminated in red light. Alongpass filter allowed only wavelengths in the infrared region to reach the camera sensor, permitting the researchers to reveal the hieroglyphs non-invasively.
Beyond these two breakthroughs, the research team is pursuing whether there is a single, optimal way to acquire and analyze multispectral imaging data of archival material, with the long term goal of preserving cultural heritage for future generations. To achieve this, the team is using multispectral imaging on historic documents beyond Egyptian papyri. For example, samples of a circa 1753 manuscript were imaged prior to and following damage to allow for the the development of a multispectral imaging approach (combined with appropriate image analysis) to recover the writing therein. This multispectral imaging variant used wavelengths between 400 and 900nm. Importantly, the imaging may provide information not only about the writing itself, but also about how the document was written (for example, to analyze the chemical composition of the ink).
Needless to say, many people beyond Gibson and Terras are involved in this fascinating research, including Dr. Kathryn Piquette from the UCL Centre for Digital Humanities’ Advanced Imaging Consultants (UCLAiC), PhD student Cerys Jones from the EPSRC Centre for Doctoral Training in Science and Engineering in Arts, Heritage & Archaeology (SEAHA), Michael B. Toth from R. B. Toth Associates, Christina Duffy from the British Library, and Alejandro Giacometti who at the time was a PhD student at UCL. But the research team is much bigger. The papyrus imaging project alone involved at least a multinational collaboration of 25 people from 14 institutions.
The research received support from at least 9 funders (the Arcadia Fund, R B Toth Associates, SEAHA, EPSRC, the Petrie Museum of Egyptian Archaeology, ChiddingstoneCastle, Sussex Egyptology Society, UCL Advanced Imaging Consultants, UCLDH). Prof Gibson’s blog acknowledges this shortlist is likely incomplete.
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