The Victoria and Albert Museum
While the identity of the man is unknown, attempts have been made to deduce his profession from his costume and the staff he carries. Some believe him to be a centurion with a staff of office or a tibicine (player of a tibia or early musical instrument).
The Romans perfected this technique for making gold pendants and bowls of sandwich glass, in which the glass-blower applied gold-leaf to the outer surface of a bubble of molten glass. In these instances, the glass was either colorless, or a variation of pale blue, green or purple. The portrait was created with a needle point which was used to scratch and stipple the gold-leaf. In the last step, the glass-blower would press a second bubble of colorless molten glass against the first - thus trapping the decorated gold-leaf between the layers. Hence, the name, “sandwich glass.”
Portrait medallions such as these were employed as decorative pendants, but most were set into the base of commemorative bowls—often given as wedding gifts. The portraits were later broken out of the dishes and used as to adorn grave markers in much the way glazed photos adorn modern tombstones.