portraits, some of which are considered very realistic as well. Gold glass Gold glass, or gold sandwich glass, was a technique for fixing a layer of gold leaf with a design between two fused layers of glass, developed in Hellenistic glass and revived in the 3rd century AD. There are a very few large designs, including a very fine group of portraits from the 3rd century with added paint, but the great majority of the around 500 survivals are roundels that are the cut-off bottoms of wine cups or glasses used to mark and decorate graves in the Catacombs of Rome by pressing them into the mortar. They predominantly date from the 4th and 5th centuries. Most are Christian, though there are many pagan and a few Jewish examples. It is likely that they were originally given as gifts on marriage, or festive occasions such as New Year. Their iconography has been much studied, although artistically they are relatively unsophisticated. Their subjects are similar to the catacomb paintings, but with a difference balance including more portraiture. As time went on there was an increase in the depiction of saints. The same technique began to be used for gold tesserae for mosaics in the mid-1st century in Rome, and by the 5th century these had become the standard background for religious mosaics. The earlier group are "among the most vivid portraits to survive from Early Christian times. They stare out at us with an extraordinary stern and melancholy intensity", and represent the best surviving indications of what high quality Roman portraiture could achieve in paint. The Gennadios medallion in the Metropolitan Museum of Art in New York, is a fine example of an Alexandrian portrait on blue glass, using a rather more complex technique and naturalistic style than most Late Roman examples, including painting onto the gold to create shading, and with the Greek inscription showing local dialect features. He had perhaps been given or commissioned the piece to celebrate victory in a musical competition. One of the most famous Alexandrian-style portrait medallions, with an inscription in Egyptian Greek, was later mounted in an Early Medieval crux gemmata in Brescia, in the mistaken belief that it showed the pious empress and Gothic queen Galla Placida and her children; in fact the knot in the central figure's dress may mark a devotee of Isis. This is one of a group of 14