Previously published results have preliminarily characterised the prehistoric production (12th-3rd century B.C.) of black slipped pottery recovered from the excavations of Gotihawa, in Kapilbastu District in Southern Nepal. Some clayey materials, still used nowadays by local potters for producing vessels, have been collected in the surroundings of the site and analysed. Two different ceramic classes have been particularly investigated: the so-called Black Slipped Ware (BSW) and the Northern Black Polished Ware (NBPW). So far it has not been possible to define clearly distinctive markers of these on the basis of either archaeological studies or archaeometric analyses. The main result obtained for the NBPW and BSW pastes is the high compatibility with the examined clays. The use of local clays for artefacts manufacturing is therefore assured. More interesting information is obtained by analysing the glossy layers of the two classes. Three groups of glosses have been evidenced in which the differences are related to the different amounts of potassium, iron and aluminium oxides. The glosses of the Al-group present values of aluminium higher than the corresponding pastes; in the AlFe-group glosses the quantities of aluminium and iron are very high, and finally in the third group (KAlFe) all three elements are more abundant than in the pastes. Practically all the BSW glosses fall in the AlFe group, while the NPBW glosses are distributed in the three groups. Other information regarding working techniques, in particular the firing conditions of the artefacts, have to be clarified in order to assess the whole manufacturing process. The detailed reconstruction of the firing techniques of such artefacts with the usual analytical methodologies (XRF, XRD and observation in thin section) is highly problematic due to the peculiar features of the samples. The low calcium content gives rise to an extremely simple mineralogical composition, without any of the calcium silicates which usually form during firing, and give indications on the firing temperature. Moreover, the absence of crystalline iron oxides in the diffractograms limits the possibility to evaluate the firing temperature to the sole estimate of illite content. The determination of the firing atmosphere is mainly based on a visual examination of the colour of the sample pastes and slips. In an attempt to better define the range of firing temperatures, we have chosen to use Mo¨ssbauer spectroscopy on the basis of the high content of iron of the samples. In fact, 57Fe Mo¨ssbauer spectroscopy allows the identification of mineral phases to be used as a ''mineralogical thermometer'', such as spinel phases, hercynite and metallic iron. Also, the calculation of the reduction index (Fe2þ/FeTOT) yields interesting information regarding the firing technology, and particularly the control of the firing atmosphere by the potter. These results seem to be possibly linked to previous data obtained from the EDS chemical analyses of the above-mentioned three groups of slips.
Firing techniques of black slipped pottery from Nepal (12th-3rd century BC): The role of Mossbauer spectroscopy
Gualtieri S;Fabbri B;
2008
Abstract
Previously published results have preliminarily characterised the prehistoric production (12th-3rd century B.C.) of black slipped pottery recovered from the excavations of Gotihawa, in Kapilbastu District in Southern Nepal. Some clayey materials, still used nowadays by local potters for producing vessels, have been collected in the surroundings of the site and analysed. Two different ceramic classes have been particularly investigated: the so-called Black Slipped Ware (BSW) and the Northern Black Polished Ware (NBPW). So far it has not been possible to define clearly distinctive markers of these on the basis of either archaeological studies or archaeometric analyses. The main result obtained for the NBPW and BSW pastes is the high compatibility with the examined clays. The use of local clays for artefacts manufacturing is therefore assured. More interesting information is obtained by analysing the glossy layers of the two classes. Three groups of glosses have been evidenced in which the differences are related to the different amounts of potassium, iron and aluminium oxides. The glosses of the Al-group present values of aluminium higher than the corresponding pastes; in the AlFe-group glosses the quantities of aluminium and iron are very high, and finally in the third group (KAlFe) all three elements are more abundant than in the pastes. Practically all the BSW glosses fall in the AlFe group, while the NPBW glosses are distributed in the three groups. Other information regarding working techniques, in particular the firing conditions of the artefacts, have to be clarified in order to assess the whole manufacturing process. The detailed reconstruction of the firing techniques of such artefacts with the usual analytical methodologies (XRF, XRD and observation in thin section) is highly problematic due to the peculiar features of the samples. The low calcium content gives rise to an extremely simple mineralogical composition, without any of the calcium silicates which usually form during firing, and give indications on the firing temperature. Moreover, the absence of crystalline iron oxides in the diffractograms limits the possibility to evaluate the firing temperature to the sole estimate of illite content. The determination of the firing atmosphere is mainly based on a visual examination of the colour of the sample pastes and slips. In an attempt to better define the range of firing temperatures, we have chosen to use Mo¨ssbauer spectroscopy on the basis of the high content of iron of the samples. In fact, 57Fe Mo¨ssbauer spectroscopy allows the identification of mineral phases to be used as a ''mineralogical thermometer'', such as spinel phases, hercynite and metallic iron. Also, the calculation of the reduction index (Fe2þ/FeTOT) yields interesting information regarding the firing technology, and particularly the control of the firing atmosphere by the potter. These results seem to be possibly linked to previous data obtained from the EDS chemical analyses of the above-mentioned three groups of slips.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.