Manufacturing Techniques of Byzantine Bricks

Manufacturing techniques of Byzantine bricks

Our knowledge on Byzantine brick manufacturing is based on excavations, laboratory tests and observations, very limited written sources and the traditional technology of brick manufacturing, which is rather simple and remained without significant alterations from the medieval period until the industrialization of production at the end of the 19th century.

The traditional productive procedure, as survived in old workshops existing in Greece until the middle of the 20th century, followed four stages : digging the clay out of the fields, molding of the product, drying of the bricks at the open air and firing.

Matters related with the location of brick kilns, distance between kilns and dwellings and neighboring kilns were regulated by Byzantine legislation. The clay was taken from selected clay fields located at the vicinity of the workshops, out of the cities and villages, from superficial layers of ground (0,5-1m deep) and was put in permanent pits, 1,5-4m wide and 0,6-0,8m deep paved with stones or bricks. There was mixed with water and remained over a period of one day to one week and then was worked by feet and spade. Clay for bricks was not submitted to purification, as was necessary for fine clay products (pottery).

When brought out of the pit clay was worked by hands to be soft and plastic, remained covered with wet textiles or straw to prevent quick drying, and all the so prepared quantity had to be molded until the end of the day. Moulds were made of wood or metal and in earlier periods (up to 6th century) were provided with a bottom baring a curved seal. In later periods the mold was bottomless and bricks stamps are lacking. Bricks were left out on a leveled field until the next morning ( first stage of drying) and then were stored under open sheds to dry slowly for three to six days. For final drying they were taken out, covered with tiles, for three or four more days.

Firing was taking place in built two-storied kilns or in temporary long heaps at open air, where bricks were placed together with the fuel. Kilns give the best products, while the firing at heaps give a great proportion of under fired or over fired products.

The lower level of the kiln, always subterranean, is the firing chamber and the upper the baking chamber for bricks. The kiln is built of bricks with clay mortar, its interior plastered over with clay mortar, and its exterior dressed with a thick stone wall. The floor of the baking chamber, carried on built arches and pierced with many holes, is almost at the same level with the ground. Brick kilns are usually rectangular, but those of circular form were producing bricks of more uniform firing. In any case the center of the kiln gives the best fired bricks. Laboratory tests give c.700*C as the most usual firing temperature of Byzantine bricks.