Mosaic glass fragment decorated with New Comedy theatrical half masks depicting a Seilenos with opaque lightcoloured face, black mouth outlined by red lips and green ivy set in a translucent blue matrix.

To achieve this type of mosaic glass, numerous polychrome glass canes were laid side by side to create a picture, then fused by pouring the vitreous matrix over the canes, leaving it to cool, and finally drawing it out so that the design became miniaturised. Slices were then cut, or sawn. Theatrical mask bars were made up in halves, cut and then joint up together to make a whole.

It seems likely that most glass plaques of this type were manufactured in Alexandria, but they seem to have had a wide distribution and may have been imitated elsewhere. The period of production is not certain although a small amount of archaeological evidence suggests that the bulk belong to the 1st century AD, and such a date is consistent with the style of masks represented in the series.