Romano-Egyptian Mummy Portraits from Tebtunis, Egypt

Roman-Egyptian portraits created in Egypt from the 1^st-3^rd centuries AD are often considered to be antecedents of Western portraiture. Painted on wooden panels using wax as a binding media, these visages of the dead were originally attached to mummies prior to burial.  A key archaeological site to understand this tradition of painting is Tebtunis, located in modern-day Umm el-Breigat on the southern rim of the Fayum depression. Two Oxonian archaeologists, Bernard Grenfell and Arthur Hunt, excavated the site during the winter months of 1899-1900. More interested in the papyri than the diverse material culture unearthed, the majority of the finds went unstudied at the time. Amongst these objects was a significant collection of portraits and panel paintings now housed at the Phoebe A. Hearst Museum of Anthropology at the University of California, Berkeley. One of the largest collections of Roman portraits to have remained intact since excavation, they present a rare opportunity to study how ancient paintings were made.

The Hearst portraits were studied using non-destructive and non-invasive imaging techniques that extract information about their underlying shape and color. Using a computational imaging algorithm called photometric stereo, quantitative measurements were made of brush and tool marks. Superposition of different layers was also determined to establish the order of painting of the various elements of decoration. Hyper-spectral imaging data was collected between the UV through NIR for measurements of color.  These color data were mined using machine-learning algorithms to identify pigments on a pixel by pixel basis. Using this information as a guide, micro-samples of paint were removed from discrete areas and prepared as cross-sections for a ground truth determination of the colorants used. These cross-sections were analyzed using a combination of Raman and scanning electron microscopy which revealed a rich palette of both organic and inorganic pigments that included a variety of iron earths, red lead, as well as indigo and Egyptian blue. The specific information obtained about painting methods and the overall distribution of pigments produces groupings of portraits made of similar materials and has led to the identification of ancient workshops and the hand of specific artists.