1. Written documentation

The term «yalopsos», a glassmaker, and the activities linked with it can be found already in early Byzantine codices and hagiological texts.¹ Later texts contain much less information, but they do confirm the existence of glass-making activity in Byzantine Constantinople.

The Theodosian Code (439) mentions glassmakers among the craftsmen that were granted tax-exemption,² while John Moschos³ talks about the existence of Jewish glassmakers in Constantinople. Paul Silentiarios, a member of Justinian’s court, in his Ekphrasison St Sophia,⁴ vividly describes the polycandela, where the glass ouriachoi were placed. During this early period there are no specific references on glass-making workshops in the city. It is possible that these were not situated within the city, especially if the study of the architect Julian from the Palestinian city Askalon had been taken into account; written between 531 and 522, it mentions that the glassmakers’ workshops should be situated outside the towns because of the danger of fire.⁵

Written sources on glass working in the Middle Byzantine period in Constantinople are scarce. TheBook of the Eparch by Leo the Wise (912) does not mention a glassmakers’ guild in the capital. However, there is evidence of glass production in Constantinople and of the existence of a workshop inside the city during the Byzantine Middle Ages in the Miracles of St Foteini. This text describes that a fire broke out in a glassmaking workshop (‘εργαστήριον υελοψεστικόν’), situated on the road leading from the Strategion to St Sophia (fig. 1), and that it also spread in the quarter of the coppersmiths.⁶ The remaining surviving information comes from inventories, typika of monasteries and notary texts, which attest, among other things, to the existence of glass objects as part of the equipment of a monastery or a middle-class household.⁷

2. Evidence from excavations

2.1. Glass finds in St Polyeuktos (Saraçhane)

The church of St Polyeuktos was situated in one of the main roads of Constantinople, the Mese, and was attached, according to archaeologists, to the palace of Anikia Juliana.⁸ Excavations from Saraçhane, despite some chronological gaps, offer the most credible evidence concerning glass working activity in the Byzantine capital so far. Finds from the 6^th and 7^th centuries include mainly drinking vessels and lamps, but also glass fragments. Most glass objects belong to the 11^th, 12^th and 13^th centuries and are, apart from the aforementioned objects, fragments of bracelets of several types.

Glass vessels dating in the 6^th and 7^th century mainly consist of wine glasses on a stem that leads to a disk-like base. They are simple, clear, without decorations and of a soft green or yellow colouring. This type of drinking vessel can also be found in the Aegean and the greater Mediterranean area; it is difficult, therefore, to securely assume that these glass objects were manufactured locally. Local manufacture of glass can be verified by other significant finds, as far as quantity is concerned; these are oil lamps, and lamps with three handles.⁹ Fragments of rectangular glass pieces in several pale yellow, olive green and light blue colourings can also be dated to the early Byzantine period. They have been constructed with the cylinder method, already known from Roman times.¹⁰

Only a fraction of the Middle Byzantine glass finds from St Polyeuktos can be securely dated to the period under study. It appears that the major vessels continue to be wine glasses and lamps; these look so similar, that it is difficult to distinguish between them. The main divergence from the previous period is the abandonment of the yellow colouring of vessels; this is also evident in middle Byzantine glass pieces. Among them, disc-shaped pieces can be dated with certainty and they are made with the mouth-blown glass discs technique.¹¹

The remaining finds, even two enamel vessel fragments, are unique and cannot lead to any conclusions concerning the glass working activities in Constantinople during this period.

2.2. Pantokrator and Chora monasteries: stained glass windows

The excavations of the churches of Pantokrator (Zeyrek Camii) and Chora (Kariye Camii) in Constantinople brought to light coloured glass windows (vitraux), published by Arthur Megaw in 1963 (fig. 2).¹² The first group of these glass windows has been dated around 1126, while the second one ten to twenty years later.

Near the glass finds of the Pantocrator there were also lead plates, in the shape of an H, where the glass would be decorated with whole figures (fig. 3). Lead straps must have been used to hold the window panels with the glass boards together. These rectilinear glass fragments have been cast in disks and then cut in the required shapes. The finds in Chora that are similar to quantity and shape were accompanied by lead straps forming a frame with a geometrical theme.

Due to the iconographic programme of the glass windows and their colours, and due to the inscriptions accompanying them, Megaw assumed that the technique for making stained glass was a Byzantine invention that later spread to the West.¹³ Jean Lafond disputed this opinion, arguing that the West influenced Byzantium, during the period of the Latin occupation of Constantinople (1204-1261).¹⁴

Apart from the fact that the Constantinopolitan finds are placed to an earlier date, recent chemical analysis proved that western European cathedrals were decorated with stained glass windows of a different artistic tradition.¹⁵ What is more, glass fragments of several shapes and colours in the extramural basilica in Philippi, dated to the period of Justinian (second phase), and lead bands that were found during the excavation of the Museum basilica¹⁶ in the same city offer further evidence on the early presence of stained-glass technique in the Greek world.

3. Byzantine glass objects in collections and museums

3.1. Minor-glass working

Nothing is known of the conditions of minor-glass production in Constantinople; however, it should be mentioned that a large number of glass jewellery, amulets, σταθμίων and cloisonné enamels, has been found that could be attributed to the imperial workshops. Today they are scattered in collections and museums all over the world. A significant example comes from a pair of bracelets, ornamented with valuable stones and glass (fig. 4a); these probably derive from the capital, as they resemble the wristlets worn by Theodora’s servants in the mosaic of St Vitale in Ravenna (fig. 4b).¹⁷ Frescoes and mosaics in general, as well as manuscript details, often depict lavish examples of clothing, but also of books and sacred objects, thus informing us of additional uses of glass in their decoration.¹⁸

3.2. The Treasury of San Marco in Venice

The collection of treasures in the San Marco Treasury includes, among other things, a series of luxurious vessels, thought to be part of the spoils of the Crusaders, brought from Constantinople after 1204. The most renowned among them, the cup of San Marco (fig. 5) bears gold decorations and clear coloured enamel. It is dated to the period of the Macedonian dynasty, because of the archaic motifs in its decorations and the pseudo-Kufic characters inscribed on it.¹⁹

4. Glass tesserae

Glass tesserae were probably produced in mass quantities and in several places. Constantinople must have evolved into an importance location of coloured tesserae production, since mosaic decoration was the most wide-spread type of decoration in churches and palaces. There is, in fact, an account of an Arabian prince, who requested from the Byzantine emperor tesserae for the decoration of his new palace.²⁰

5. Evaluation

Our information on glass-working in Byzantine Constantinople is too fragmented and unclear to answer questions about production and distribution of Constantinopolitan products and about Constantinople’s presence within the glass-making activity of the period. Excavations have not yet confirmed the existence of a glass-making workshop in Constantinople. On the contrary, other areas, such as Corinth and Sardis, have shown clear evidence of Byzantine workshops and mass production of glass objects.²¹ Therefore, we could suppose that Constantinople was not a very significant production centre for glass objects. It is possible that its production was just enough to cover the city’s needs; glass was imported as feedstock and glass-workers processed it. Besides, recycled use of glass trimmings was a common practice of glass-workers in every period.²² The shipwreck of Serçe Limani opposite Rhodes has brought to light 3 tonnes of glass, ready to be processed. It had been loaded in Syria and, according to the latest studies, was on its way towards a Byzantine centre.²³ Why not Constantinople?