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

Abstract

Raman 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.

Rare Crucible from Medieval Karelian Hillfort: Mineralogical Fingerprints of Functional Use

“…In contrast to thorough archeometric research of medieval Karelian kitchenware [17][18][19][20][21], the technical ceramics remain overlooked by archeologists, being only mentioned [27] (pp. 105,198-199,231,247,274-275) or preliminarily counted for pieces that could be attributed to crucibles [25] (pp.…”

“…The crucible was attributed to the technical ceramics, as it is characterized by the signs of intensive thermal treatment including vitrification, bloating of the ceramic fabric, and numerous cracks (Figure 2a,b). However, based on the reconstruction of available remains of the crucible, its volume was estimated to be not less than 500 ml, which is In contrast to thorough archeometric research of medieval Karelian kitchenware [17][18][19][20][21], the technical ceramics remain overlooked by archeologists, being only mentioned [27] (pp. 105,198-199,231,247,274-275) or preliminarily counted for pieces that could be attributed to crucibles [25] (pp.…”

“…The model experiments [46] showed that the heating of hematite was accompanied with the intensity increase of a band centered at 680 cm −1 in hematite Raman spectra. The band intensity ratio (680/620), which increases with a firing temperature rise, was used to estimate the firing temperature of wheel-thrown pottery [21] from Karelian hillforts. It has been shown [21] that the intensity ratio (680/620) for most of the local pottery samples varied from 0.8 to 1.5 (Figure 7c).…”

“…Mineralogical methods have already been applied to study Karelian medieval pottery from the hillforts located on the north-western shore of Lake Ladoga [17][18][19][20][21]. During the Middle Ages (10-15th century) the territory of the North-Western Ladoga area and the Karelian Isthmus were occupied by the Karelian people, whose material culture has a long history of archeological research and has previously been described [22][23][24][25][26][27][28].…”

GeoRaman

“…A detailed study of the Leman Album, present in the V&A collection (London) is presented by Burgio et al, [40] including the characterization of arsenic sulfide glasses as unusual pigment used as substitutes for orpiment and relagar. The combined Raman, SEM-EDX, XRD study of the mineral phases present in archaeological ceramics coming from Karelia (Russia) allowed Chazhengina et al [41] to determine their firing conditions, in terms of temperature and atmosphere. Another combined investigation, based on Raman spectroscopy but supported by XRF, SEM-EDX, FTIR and HPLC, which allowed Klisinska-Kopacz et al [42] to reconstruct the history, in terms of manufacturing process and provenance of the materials, of Ko sciuszko banknotes, one of the oldest paper banknotes in Europe.…”