Study of medieval ceramics excavated at the monastery of Karaachteke (Varna, Bulgaria)
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2015-01-01
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Various medieval unglazed and glazed ceramic artifacts discovered during archaeological excavations at the monastery of Karaachteke near Varna (Bulgaria) are for the first time chemically and structurally characterized by ICP-OES, XRD, SEM-EDS and the Archimedes method aiming to understand the technology of medieval ceramics production. The unglazed artifacts water absorption ranges from 10 mass % to 15 mass %, which indicates that the ceramics are well sintered and most probably fired at a high temperature, ca 950°C - 1050°C. The artifacts contain a certain amount of coloring oxides (Fe<inf>2</inf>O<inf>3</inf> + TiO<inf>2</inf>), which determine their slightly red color. The phase composition indicates the presence of crystalline phases of quartz and plagioclase, the amount of which differs in the different samples. SEM proves the presence in the sintered ceramic body of coarse quartz grains having a size of 0.05 mm to 0.3 mm. This leads to the conclusion that highly sandy clay or ceramic body containing red firing clay and coarse grain quartz sand was used. The study of the glazed artifacts proves that a transparent lead glaze prepared at a firing temperature of ca 950°C - 1050°C was widely used in the Middle Ages. Some of the objects are typical sgraffito pottery, which indicates that the ceramic masters during this period could produce ceramic bodies, engobes and glazes using different raw materials compositions. Other glazed artifacts refer to the type of the famous Preslav ceramics having a white ceramic body and transparent green glaze of the Seger formula PbO.0,16Al<inf>2</inf>O<inf>3</inf>·2SiO<inf>2</inf> and firing temperature higher than 1000°C.