The Pompeiian ‘Blue Room’: in situ detection and economic estimation of Egyptian blue pigment in an ancient domestic sacrarium

Egyptian blue (EB) was a prized, intense blue pigment in antiquity, its color commonly associated with wealth, status, and divinity. While frequently used in small quantities for decorative enhancements, Pompeii’s newly excavated “Blue Room”, a shrine in Regio IX Insula 10, is remarkable in that the entire room is covered with this historically famous pigment. Using a combination of visible (white light)-induced luminescence, SEM-EDS, and Raman spectroscopy, we were able to spatially map the large-scale distribution of EB in situ, identify the method of application, and calculate the total quantity of EB used. We estimate that between 2.7 and 4.9 kg of EB was applied in the fresco technique, corresponding to a total cost of between 93 and 168 denarii. These findings demonstrate how modern multi-scale characterization tools can be employed to provide valuable insights into material investment, artistic practice, and social status in an ancient Roman domestic context.