Roman glass: Art and technology in a 4th century A.D. opus sectile in Ostia (Rome)

Abstract One of the most important Roman opus sectile (inlaid of stones and other materials to make a picture or pattern) is the both figurative and geometric decorated panel ensemble dating to the end of the 4th century A.D., discovered in 1959 near Porta Marina (Ostia, Rome) and now exposed in the National Museum of Early Middle Ages in Rome. A recent revision of the 190 panels provided an opportunity for a careful examination of the materials used. The only nonstone material used in the decoration is vitreous paste: it was used to make the entire mosaicated ceiling and in some other areas beside opus sectile . Monochrome vitreous materials of varying colours have been identified (among them several red tones), as well as polychrome materials imitating marbles ( serpentino and red marble), precious stones and mosaic materials (gold foil tesserae and opaque glass pastes coloured in several shades from green to blue and less frequently in red and black). Forming, cutting and shaping techniques of the vitreous materials were also investigated. Furthermore, analytical investigation of glass pieces and mosaic tesserae was performed in order to ascertain which melting, colouring and opacifying techniques were adopted to prepare these materials.