Lycurgus cup: the nature of dichroism in a replica glass having similar composition

The dichroic nature of Lycurgus cup glass exposed at British Museum and prepared by ancient roman glassmakers (IV c. AD) is still exciting the researchers minds and for this reason a series of replica glasses with optical properties and composition similar to Lycurgus cup glass has been prepared by secondary heat treatment. The glass microstructure has been investigated by SEM showing the occurrence of a phase separation in the form of droplets enriched with silica which crystallizes over time into the ?-quartz. The phase separation is due to the Fe2+, Fe3+ and P2O5 species that could enter the glass batch occasionally as also made by Au and Ag nanoparticles (NPs). The NPs size has been estimated according to Mie theory. It has been proposed that the wine-red color in transmitted light is due to the absorption of light by the metal NPs, whereas the olive-green color of glass, in reflected light, is mainly caused by Fe2+ and Fe3+ absorption and Rayleigh scattering on droplets.