ИСТИНА

Study of thin sections of ceramic materials under petrographic microscope is widely used to identify the composition and abundance of its main components, and to trace some technological processes, which leave specific imprints in the ceramic micromorphology. We applied the micromorphological analysis to the archaeological ceramics from Volga Bulgaria – a powerful state which flourished in the Eastern Europe (Volga and Kama rivers confluence) between 7th and 13th centuries AD. The study was focused on the micromorphology of the sphero-conical vessels: abundant (more than 6000 exemplars found until now) but still enigmatic type of ceramic ware present in various sites of Middle Volga basin dated to the interval between 10th and beginning of 15th centuries. The function of these small (8-15 cm high) vessels is still debated: mercury containers, perfume jars, bottles for drinking water, lamps and even architectural features я бы лучше написала elements. Sphero-conical vessels have thick walls made of refractory material with high density and hardness (5-8 on the Mohs scale) acquired due to careful selection of clays, their pretreatment, and high-temperature firing. Two groups of these vessels are discriminated in the Middle Volga region by the colour: 1) red; 2) grey and yellow. The objectives of the study are: to establish the composition of clay paste and inclusions (natural and added as temper); to reconstruct temperature and technology of firing; establish the region of origin. The materials were collected at the sites: Bilär (10 samples), Bilär II (2 samples), Bolgar (10 samples). As a reference, 1 fragment of the Middle-Asian sphero-conical vessel (Termez, Uzbekistan) was also investigated. In all cases the clay paste was isotropic that points to high-temperature firing. The composition of coarse inclusions showed major differences. Part of the samples contained silt or fine sand particle consisting of quartz (predominantly) with admixture of K-Na feldspars and mica. These components resemble mineralogical composition of the alluvial deposits and mantle loams of Middle Volga region; thus the corresponding ceramic ware could be of local production. Some samples however contain coarse angular grains of fresh plagioclases, fragments of basic rocks. These materials are exotic for the studied region and suppose that the wares were imported. The type and abundance of pores also differs: most samples have only few pores of irregular shape, but some demonstrate also thin discontinuous fractures. In few thin sections we observed the layer of glaze on the outer surface. The study of bulk chemical composition combined with micromorphology also contributed to the identification of the origin: local ceramic is low-calcium whereas imported vessels have high Ca and lower Fe content. Micromorphological investigations combined with other geoarchaeological methods made significant contribution to the hypotheses about the origin of sphero-conical vessels in the Middle Volga medieval sites. The research was accomplished with the financial support of the Russian Foundation for Basic Research within the framework of the Project No.14-06-31184 «Sphero-conical vessels of Volga Bulgaria».