Researchers have discovered traces of the pigment Egyptian blue on the underdrawings of 15 Roman-era portrait mummies from the Phoebe A. Hearst Museum of Anthropology at the University of California, Berkeley. The collaboration with the Northwestern University in Evanston, Illinois, also showed it was used for modulating colour. Marc Walton, a professor of materials science and engineering at Northwestern, says the discovery “defies our expectations of how Egyptian blue would be used”. Scholars had previously assumed that the pigment was too expensive to be used for preparatory purposes. The study was published in the journal Applied Physics.