The Petrographic Analysis of Thin Sections on the Non-Glazed Painted Pottery Ceramics of Islamic Era in Qeshm Island

Qeshm Island is located in the northern coast of the Persian Gulf in the estuary of it in the span of Hormouz channel and its location on the communication routes have long affluence extensive commercial communications with other areas. During Archeological surveys were carried during two seasons in 2007 and 2012 by Ali Reza Khosrowzadeh were identified 161sites and a considerable number of marked potteries too which they are important. This type has a wide distribution in the northern and southern coasts of the Persian Gulf and appears to have spread throughout the northern and southern coasts of the Persian Gulf during Islamic times. But most of archaeological researches have been concentrated on the south of the Persian Gulf and archaeological information from the northern area is scattered and inadequate. Therefore, in order to identify and introduce this lesser known type of Pottery in Iran and for its mineralogical purpose14 sampled unglazed painted potteries were selected for microscopic examination and the samples were analyzed by thin section petrographic analysis using polarizing light microscope. The microscopic studies were an attempt to answer the questions: What are the mineralogical characteristics of Qeshm Island potteries? What are the similarities and differences in minerals among the tested samples? how is the quality and amount of making potteries? Considering Qeshm is located in the Zagros structural zone due to its geological location that saws the carbonate sedimentary and sandstone. These characteristics correspond with the findings of the potteries from Qeshm. The most common mineral in the sample structure is quartz and all samples have but one sample of grog, but some different minerals and rocks are remarkable in the samples. Furthermore, all the pottery samples have the same structure and porphyry texture. Iron oxide was used in the color of all samples. The most potteries are baked at a temperature of about 8000C. So most of them have enough baking.
Keywords: Non-Glazed Painted Pottery, Islamic Era, Petrography, Persian Gulf, Qeshm Island..
 
Introduction
Archaeologists have focused on Islamic archaeological sites in southern coast of Persian Golf more than other sites. However, despite the importance of the northern coasts of the Persian Gulf during the Islamic era, no Islamic sites have been explored on the Iranian coasts of the Persian Gulf. For this reason, the knowledge and awareness of researchers about the quantitative and qualitative characteristics of painted pottery on the northern coast is very little and insignificant and there is no information about the mineralogy of pottery on the site for researchers.
Therefore, it is necessary to study the petrography of unglazed pottery of the Islamic era as a common and important type of pottery from the collection of pottery obtained from two chapters of Alireza Khosrowzadeh’s study in Qeshm.
About 3500 potteries of different types have been found through these two studies. 14 samples of them are unglazed earthenwares found through first chapter, belong to Middle Islamic era until the end of the late Islamic era and were selected for petrographic studies.
Petrographic studies of the mentioned samples is done with the aim of providing accurate information about the characteristics and amount of minerals in the selected earthenware pieces, as well as the method and amount of fired painted earthenware’s of the Islamic era of the northern coasts of the Persian Gulf to benefit researchers and facilitate subsequent comparative studies and comparison of the results of the present petrographic experiments by findings of the southern Persian Gulf areas (especially Oman and UAE) with a focus on unglazed earthenware’s of Qeshm Island in order to understand the cultural relationship between them, and to respond to questions like this: What are the characteristics of Qeshm Island in terms of mineralogy? What are the similarities and differences among the samples in terms of minerals? And what is the quality and level of firing of these earthenware’s?
 
Identified Traces
For petrography of potteries, 14 samples of unglazed pottery related to Qeshm Island, which belonged to the Timurid period to the Qajar period, were presented to the Petrography Laboratory of the Faculty of Natural Resources and Earth Sciences in Shahrekord University of Iran. Based on the results obtained from the study of the samples, it was observed that the filling components are divided into the following two groups based on the source:
1) Of igneous or metamorphic origin, including quartz, feldspar, Plagioclase feldspar, pyroxene, and small amount of mica
2) Of sedimentary origin including parts of dolomite, microcrystalline lime, siltstone, fossilized lime and small amount of sandstone
The studied samples are classified into six subgroups based on the similarities and differences of mineralogy
Interestingly, the texture of all samples is porphyry. The most common mineral is quartz. All specimens except the sample number 6 have grog; the lime and calcite in the specimens have been destroyed. This condition is due to the heating at temperatures above 800 C and the use of organic fuel. This mineral is destroyed at a temperature of about 800 degrees (Emami, 2010: 275; Rothossi, 2010: 856). The surface of most specimens contains iron oxide.
In group one, sample 1 has a small amount of feldspar, and in sample 3 of the same group, a small amount of sandstone was observed. Group 2 also differs from other groups by having some feldspar, mica, and pyroxene. Group 3 has some plagioclase and plagioclase feldspar. Group 4 contains small amounts of plagioclase, feldspar and mica particles. Group 5 samples have a small amount of pyroxene and lime, and group 6 contains some Plagioclase feldspar and calcined dolomite particles.
 
Conclusion
Based on the results of petrographic experiments on 14 specimens of unglazed pottery from the Islamic era in Qeshm Island, it was observed that these potteries have elements of igneous origin such as quartz, feldspar, Plagioclase feldspar, collagen, pyroxene and a small amount of mica. All potteries has a porphyry texture, so the surface of the pottery is rough. In all cases, quartz is monocrystalline. Examples of Borka Khalaf 1, Samar 2 and Talagour 1 have angled to semicircular quartz. The geometric shapes of the angled margins to semicircular quartz indicate the change of all the constituent components relative to the original source or the addition of these materials as auxiliary materials. Iron oxide has also been used in the painting of potteries. All specimens except sample 6 have grog.
Comparing the minerals of the samples, the differences are interesting. In group one, a small amount of feldspar is seen and in sample three of the same group, a small amount of sandstone is seen. Group 2 also differs from other samples by having some feldspar, mica and pyroxene. Group 3 has some plagioclase and Plagioclase feldspar. Group 4 contains small amounts of plagioclase, feldspar, and mica particles. Samples of group 5 have a small amount of pyroxene and lime, and in group 6, some Plagioclase feldspar and calcined dolomite particles have been observed.
   In answer to the third question, petrographic studies show that there is not much control over the heating and baking of such potteries. The main mineral in limestone is calcite, and if it is not present in limestone, it means that the baking temperature of the pottery was more than 800 degrees. In samples 1 and 2 of the Borka Khalaf, Muzan, samples 2 and 3 of Talagour, Ramkan, Ziranak and Nakhlgol, the evidence indicates insufficient baking temperature.