Glazed ceramics

In Byzantium

In Byzantium, decorated tableware was distinguished by its lead glaze—a thin layer of transparent, shiny, colourless, or coloured glaze in shades of yellow or green, which provided waterproofing for porous clays and facilitated the cleaning of the objects. It also played a decorative role by lending a coloured, shiny aspect to ceramic objects. It was often combined with various surface treatments: decorative painting with slip, or polychrome painting, using various metallic oxides, and decoration that was stamped, incised, or excised.

To make lead glaze, artisans mixed lead oxide (between 60 and 70%) with silica sand (between 40 and 30%). They transformed this mixture by heating it in the hottest part of the oven, or more rarely, in a purpose-made oven. This was accomplished by placing the mixture in a bowl or heat-proof crucibles, which were broken after cooling to extract the frit that was then crushed and ground in a mill. Byzantine lead glaze was transparent and shiny, but never colourless. The range of colours was fairly limited. The most commonly used oxides were: iron oxide that produced brown and yellow tones, copper oxide that produced various types of green, and magnesium oxide that became purple or brown. The glaze was applied on fired objects coated in slip (a layer consisting of a mixture of clay and water in a creamlike consistency that concealed the colour of the clay and created decorative effects) in the form of frit suspended in water, to which the potters added organic products to the make layer of glaze more cohesive on the surface of the ceramics. The glaze was applied with a brush or a cloth, which only required a small quantity of glaze applied in several stages in order to cover the piece in a uniform way. This technique was ideal for applying various bicoloured glazes on the same vase. The potter could also pour the liquid quickly on a flat surface, concentrically, in order to cover the whole surface in a uniform way. They could also immerse the piece in the glaze, a rapid and efficient process for applying even layers, but which required a large quantity of glaze. In order for lead glazes to develop satisfactorily on ceramic surfaces, they need to be heated to temperatures close to 1100°C. For the artisan, this technique was quick, the glaze was easy to apply, it adhered well to the vase, and there was less chance of faults developing during the firing process. The shiny, coloured appearance of this earthenware and the ease with which it could be cleaned and used made it popular with buyers.

Lead glaze wasn't a Byzantine invention—it was developed in Mesopotamia, during the Hellenistic period. It developed in Roman times along with alkaline glaze. Evidence suggests it was used in Athens around AD 360, and there are traces of it in productions from Pannonia and Raetia in the fourth century. Discoveries made in ex-Yugoslavia and North Italy show that the production of glazed ceramics continued from the fourth to seventh centuries. It was probably introduced into the workshops in Constantinople (in the seventh century) through Ravenna. This lead covering was also used in Sassanid Mesopotamia, but it wasn't until the ninth century that it came to Egypt. In northern France, there is evidence that lead glazes were used in the ninth century, but they weren't used in the south until the thirteenth and maybe even the fourteenth century. The continuous use of a particular type of glaze shows that Byzantine potters travelled little. In the Islamic world, lead, alkaline, and stanniferous glazes were often used in the same workshop, but the Byzantine workshops only used lead glaze.

The production of glazed crockery began in Byzantium at the beginning of the seventh century. Up until the tenth century, its production was centralized and its distribution was limited to large urban settlements like Constantinople, Athens, Corinth, Nessebre, Chersonese, and Otranto. Glazed whiteware, considered to be Constantinopolitan ceramics par excellence, was favoured but wasn't as widespread as general-purpose ceramics. In the eleventh century, there was an increase in the number of workshops, production diversified with the appearance of redware vases, and there was an increase in production rates. There was a reversal in the tendency for general-purpose ceramics to be favoured over glazed ceramics. Although this shows that there was an improvement in the standard of living for a part of the population in Byzantium, glazed crockery wasn't considered to be a luxury product—the aim instead was to produce decorative effects for sophisticated people who were open to new ideas and original decorations. It wasn't particularly prized in the courts, which had the means to buy gold and silver. Its appearance on the imperial table, recounted by a chronicler in the fourteenth century, reflects the poverty and decadence into which the Empire had fallen. The finds and the condition of the discoveries in urban, civil, and ecclesiastical buildings, fortified towns, and modestly sized rural fortresses, confirm that the tableware was quite ordinary and probably made for a ‘comfortable’ middle class.

V. F.