A fragment of “ancient crystalline” glass from S. Sophia was exhibited at the Society of Antiquaries in 1876. It is described as only “one sixteenth of an inch thick, and nearly colourless except for iridescence.” Grelot remarked that the plain glazing was “of round panes set in plaster,” but this must refer to the gradual filling round of the panes by repairs, as may at present be seen in the baptistery windows; although circular panes in a plaster setting were much used in Byzantine work, the glass being spun in separate discs of slightly varying sizes was inserted in marble or plaster slabs in different combinations. Windows of this kind remained in the apse of the Theotokos church twenty years ago. Dr. Covel is precise as to S. Sophia in 1676; he says the windows were “cut out of entire stone into quarries exactly square,” 10 by 12 or 14 inches. “In the first window of the west gallery (coming in on the south side), are several pieces of white transparent stone which I take to be Indian alabaster.” * * * * * Modelled stucco work was much used by late Greek, Roman, and Byzantine builders. Paulinus tells us that at Nola “a cornice of gypsum” separated the mosaic and marble of the apse. A large number of examples from the fourth to the sixth century are found in Rome, Parenzo, and Ravenna. “About the middle of the fifth century Galla Placidia built the church of S. Croce in Ravenna ‘of very precious stones, and with stucco (gypsea) modelled with the tool’ (Agnellus. _Lib. Pontif._ i. 283). Decorative stuccoes in the apse of S. Ambrose at Milan were destroyed thirty years ago, as they were supposed to be ‘Baroque.’ Dartein analysed the material and found that it contained 85 per cent. of plaster (gesso), a little lime, sand and brick-dust or pozzolana.” “The rich decoration of the Chapel of S. Maria at Cividale (eighth to tenth century), and the Arab-Norman modelled stuccoes of Sicily show that the traditions of this kind of ornament were not lost at a later time.”[411] In the churches of Greece this material is largely used, and its application in Arab work was due to Byzantine example. At S. Sophia an ornamental plaster frieze runs along both sides of the south porch: this is a scroll throwing out acanthus leaves and fruits like poppy seed-vessels. The background is coloured blue. [Illustration: FIG. 74.--Plaster Friezes of Gynaeceum.] The flat frieze-like cornice of the first floor ornamented with two patterns of leafage appears to us to be of stucco; we figure these here, but we have not been able to verify the material. If of stucco, as we suppose, it is cast or stamped in small square panels as shown: certainly some of the Byzantine plaster-work, as for instance that forming the cornice of the apse at S. Apollinare in Classe, was cast in short sections and then applied.