Study of Chemical Compounds of Sgraffito Ware: A Case Study of Shahkuh Site at Alamut

During archaeological excavations on Shahkuh site, large number of Sgraffito ware recovered. In Alamut, this type of Sgraffito ware has been obtained from Hassan-e Sabbāh Fortress, Shahkuh, and Lambesar Castle. Sgraffitos of Shahkuh are similar to other synchronous sites of Alamut region in paste, shape, thickness and inclusion. Because of similarity between potsherds of sites, probably a single source was considered the reason for this similarity. In this study, a total of 26 pieces of Sgrafito and plain pottery were selected from 2 known sites Alamut region. first aim of the research is to identify the chemical composition of the pottery of each site; The second is to understand the differences or similarities of the compositions of each site and then try to assess the possibility of producing Sgrafiato pottery of Alamut region in Shahkuh’s Kiln. After this stage it will be possible to gain an answer to these questions:  The chemical compositions of the pottery of these sites are similar or different? and how many distinct groups can be identified based on the chemical composition? How many of the sgrafiato specimens will be grouped with the unglazed specimens, and how can the relationship between the groups be explained on the basis of the archaeological-historical context? The samples of this research were analyzed by PIXE. The results were studied with SPSS and Dplot software. Three different groups recognized. First group consist of kiln sample (unglazed), second group consisted of Sgrafito samples of Shahkuh. Third group consisted of Lambsar Sgrafitos. samples of O38 was common between 1 & 2 groups. Based on these results, it was determined that the soil source of unglazed pottery inside Shahkooh kiln is different from Sgrafito potsherds. The second point is the difference between the second and third groups due to changes in the source and pottery workshop over time.
Keywords: Sgraffito Ware, Shahkouh, Lambesar, PIXE.
 
Introduction
Shahkuh site is situated at 6 km east of Rajaei Dasht. One of the important finds of Shahkuh site was the identification of a kiln where unglazed pottery was found inside the kiln. In addition, Sgraffito pottery was identified around the kiln. Due to the importance of discovery of the kiln in Shahkuh site, suitable conditions were provided for the study of the chemical composition of ware in the region and its comparison with the chemical composition of other types of ware obtained simultaneously sites in the region. a total of 26 pieces of pottery, including 21 sample of Sgraffito wares, which were obtained from Shahkuh and Lambesar and five unglazed, which were obtained from inside the kiln of Shahkuh analyzed. These samples were divided into four classes. The first class includes Sgraffito samples of Lambesar and the second one is related to the Sgraffito ware of the surface of Shahkuh site. The third class is composed of the glazed samples obtained from inside the kiln. The fourth one is a collection of the samples from O38 borehole, which continued more than four meters from the surface to the depth and includes two periods. The aim of this study is to determine the elemental composition of the ware inside the kiln and the glazed ware of Shahkuh and Lambesar areas. The aim of the study are to identify the chemical composition of pottery in each site; the second goal is to understand the differences or similarities in the composition of each site and try to assess the possibility of producing Sgraffito pottery in the Alamut region in Shahkooh. The questions in this study are: How similar or distinct are the chemical compounds of potsherds in these sites, and how many distinct groups can be identified based on chemical composition? How many samples of sgraffitos will be with the non-glazed samples in common group and how can the relation between the groups be explained based on the archeological-historical context? Archaeometry has been employed to respond to these questions. In this study, particle-induced X-ray emission (PIXE) spectroscopy has been to identify the elemental composition of the obtained glazed (Sgraffito ware) and unglazed glazed ware. In addition, SPSS and Dplot software were used to compare the ratio of the compositions in the samples and to assess the probabilities with regard to the soil resources used for ware.
 
Identified Traces
The number of 20 compounds was identified in the samples tested by PIXE method. Kolmogorov-Smirnov test was run in SPSS to examine the assumption of normal distribution of the research variables. Ten compounds, including Al2O3, SiO2, K2O, CaO, TI2O3, MnO, Fe2O3, Cu2O, PbO, and ZnO were revealed to be at the significant level. Dplot software was also used to better compare and understand the experiment results. To analyze the results, the purpose of the study should be to understand the differences between the samples, or even to identify the source; in this regard, two methods can be used as criteria. The first method is based on giving credit to the common compounds between the samples, which included seven compounds of Al2O3, SiO2, K2O, CaO, TI2O3, Fe2O3, and ZnO in this study. The other method is based on the lack of common compounds in one class and its absence in other classes. In this regard, one can refer to MgO, So3, and Cl compounds in the ware samples of the kiln that do not exist in other samples while they are present only in the two samples of Lambesar and one sample of the site. However, the abundance of measurements in these three samples differs significantly from the samples in the kiln. Moreover, Cu2O and PbO compounds are present in all samples of Lambesar, the site, and O38, but not in any of the kiln samples. Considering other factors, this can contribute to drawing conclusions and conducting analyses. In addition, 5 compounds of Al2O3, SiO2, K2O, CaO, and TI2O3 were presented in the form of graphs by means of DPlot software so that the differences among the results of each class can be understood and analyzed correctly.
 
Conclusion
Three groups were identified. Group 1 was all from unglazed samples of the kiln. The second group included samples of the Shahkuh site, which was different from the samples of other classes. The third group included samples from the Lambesar. Samples of O38 were common between 2& 3 groups. According to the excavations of Lambesar Castle, the establishment of the site dates back to the first period of Esmailid era/ Seljuq dynasty while Shahkuh site has two periods. The initial establishment of the site dates back to the first Esmailid era, and the second period goes back to the period of Esmailid new government. According to archaeological data, the oldest layer in Shahkuh dates back to Esmailid era/ Seljuq dynasty. Excavation in O38 continued from the surface (the Esmailid new government) to a depth of more than four meters. Therefore, the tested samples from this borehole included both group 1 and group 2. In addition, it was determined that no Sgraffito ware production workshop has existed in Shahkuh site. In Alamut region, Sgraffito ware production source changed with the transition from the first Esmailid period to the second Esmailid period.