The Art Institute of Chicago houses two second-century Roman-era Egyptian mummy portraits in its collection. In recent years mummy portraits have been the focus of considerable study, and the Art Institute’s examples have been examined using multiple analytical techniques in an effort to elucidate the methods and materials used in their creation. During the course of these investigations, intriguing differences between the two portraits were noted. With regard to the binding medium, one of the portraits bears the hallmark robust impasto of wax applied using the encaustic technique, and the other displays the flatter, matte appearance accompanied by the striking tratteggio and crosshatching that is often associated with tempera painting. Indeed, prior to technical examination the two paintings were perceived as such. Analysis of the binding medium of the first portrait using Fourier transform infrared microspectroscopy (FTIR) and gas chromatography mass spectrometry (GCMS) demonstrated, unsurprisingly, that it is composed of wax, supporting a description of the technique as encaustic. However, analysis of the second portrait unexpectedly also revealed the presence of wax. A limited number of published studies of media analyses of other portraits which yielded the same dichotomous results—assumed to be egg or glue based on visual appearance but found to be wax upon technical investigation—has confirmed the existence of similar objects in other collections. The Chicago painting is, consequently, one of a growing corpus of portraits that thrusts a tint of grey into an art historical construct that has been presented as quite black and white. Additionally, both portraits were examined with a combination of non-invasive in-situ scanning X-ray fluorescence (XRF) and near infrared luminescence imaging (visible induced luminescence spectroscopy, VILS). The presence of cuprorivaite, or ‘Egyptian blue’, was detected on both portraits, but its character and distribution varied startlingly between them. This discovery raises numerous questions as to the artists’ working methods, material choices, and the transmission of techniques between the Fayum region and the wider Graeco-Roman world. The analyses of the Chicago portraits, alongside collaborative work with other institutions housing similar portraits, adds to the body of information that will hopefully, ultimately address such questions. But it also serves as useful reminder that works of art often resist clear categorization since they are, after all, human creations and thus subject to the individualities and idiosyncrasies of their makers.
 
Authors: Rachel Sabino, Ken Sutherland, Emeline Pouyet, Marc Walton, Federica Pozzi