Raman spectroscopy for firing condition characterization: Case study of Karelian medieval pottery

Abstract

AbstractRaman spectroscopy together with the scanning electron microscopy and X‐ray diffraction were applied to study the firing parameters (temperature and atmosphere) of medieval pottery from Karelian hill forts in the North‐Western Ladoga region (Russia). Because the evidences of pottery manufacture including firing facilities were not discovered during the excavations of medieval Karelian fortresses, the application of Raman spectroscopy combined with the other techniques appeared to be an effective approach to reconstruct the technology of ceramic production in medieval Karelia. Scanning electron microscopy ‐energy‐dispersive X‐ray spectroscopy and X‐ray diffraction analysis showed that the Karelian pottery refers to noncalcareous and low‐temperature fired ceramics. Using the thermometer based on the thermal evolution of Raman spectral parameters of the charcoal identified in the ceramic paste of some specimens, the firing temperature for those was estimated to be close to 800 °C. These data are in accordance with the more frequent occurrence of anatase rather than rutile in the studied ceramic sherds that also corresponds to low firing temperature. The presence of hematite suggests firing in oxidizing atmosphere, in rare case the detected magnetite indicated the incomplete oxidizing atmosphere. The reconstruction of Karelian pottery firing procedure based on the obtained data supposes that the firing was carried out in bonfires. The present study contributes to the deciphering the firing conditions for noncalcareous and low‐temperature burnt ceramics, for which no significant modifications of starting minerals during heating are usually observed.