Abstract
Glaze is a prepared mixture of materials ready for application to ceramic wares by dipping or spraying. In Islamic period, decoration using the glaze was widespread. Different methods of glazing have played a major role in the beauty of glazed potteries during this period. Turquoise glazed potteries are one the significant groups of Islamic period. In this article, five turquoise glazed pottery sherds have been studied in order to identify their elements, composition and technology. The mentioned sherds dated back to 14 - 18 A.D (late Ilkhanate, Timurid and Safavid periods) , and identified from a historical house called Moravvej-e Ardabili House, in the historical part of Ardabil city. This site identified in a rescue excavation held by HassanYousefi which regarding to the cultural materials dated back to 11 - 18 A.D. The aim of this article is investigating and understanding the similarities and differences in five glazed sherds. Regarding to the mentioned point, XRD analyze applied for characterizing their phases as well as EDX analyze used for identifying the elements of glaze, and also their quantity. This research has an analytical approach and it’s method is based on analytical studies, textual evidences and comparative analyzes. According to the results obtained from analyzes, four glazes have an alkaline based and one has a lead base. Colorant oxides in glazes represent that copper used as the primary element to make the turquoise color. In general, the main elements in glazes include silica, aluminum, calcium, sodium, potassium and a negligible amount of lead. Statistical analyzes represent that the most similarities exist in sample two and sample five which belongs to the same period (late Ilkhanate and Timurid),and the most differences exist in sample four and sample five which dated back to a different periods. 
Keywords: Glaze, Turquoise, Moravvej-e Ardabili, XRD, EDX.

Introduction
In the prehistoric era, slip used as a sort of glaze in order to proof the body of the pottery, increase the aesthetical aspect of the pottery and protect the hand of the pottery maker to steak to the clay. In the historical period, using a transparent and colored glaze became widespread, but in the Islamic period the using of the glaze with various functions expanded. There are three main period in the evolution of the pottery in the Islamic era. 1. Early Islamic potteries 2. Middle Islamic potteies 3. Late Islamic potteries. During the rescue excavation in the Moravvej Historical House in Ardabil province in 2006, a vast number of pottery sherds mostly, belong to Seljuk to Safavid periods identified. This site located in the historical part of the city nearby the Sheikh Safi Al-Din Ardabili’s monument. Turquoise glazed potteries were the remarkable amount of the identified potteries in the above mentioned excavation. The questions of this article is on the subject of the turquoise glaze potteries; the amount and the type of the constructed elements ,and also study the similarities and differences between the glaze from different period. Five pieces (three sherds from 14-15 A.D and two sherds from 16-18 A.D) selected for the analytical studies with the aim of better understanding their constructed elements, technology and composition. In order to achieve to this aim, XRD and EDX analyses provided promising results about the technological aspects of the sherds, and also a comparative study not only was highly beneficial in clarifying the similarities along with differences of the composition of glazes, but also was helpful in better understanding of the turquoise glazes  in the larger region. Since there has not been applied any analytical study on the sherd identified from this site, this research would increase our knowledge about it. The pottery sherd divided into three categories, and then two samples from each category selected for the analytical studies. In the next step, technical characteristics of the sherds documented. After that, the pieces delivered to the laboratory for the analytical studies.  XRD analyses, was done in Razi Metallurgical Research Center using the Xpert Pro MPD system Panalytical model made in Poland. EDX analyses was done in Kansaran Binaloud Center using Micro Prob Horiba 7200 model made in Japan. Also, Peason Correlation Coefficient used for better understanding the correlation between different elements.

Discussion
Based on the XRD analyses, in the first sample dated back to the 14-15 AD, cristobalite, amorphous, quartz and silica were the main elements. Quartz, cristobalite and silica are the different phases of SiO2. Based on being buried,  the amount of silica decrease and the other elements increase which are shown as different picks. Quartz ingredients changed to the cristobalit as a result of increasing the temperature while baking. In the second sample dated back to the 14-15 A.D, calsite, quartz and silica phases reported. Quartz and silica represent SiO2, and calsite indicates the destruction process and release the alkaline ion from the glaze and formation on the surface of the glaze which regarding the date of the pottery and being buried, it seems reasonable. In the third sample from Safavid period , gypsum phase reported. The mentioned phase represent the destruction of the glaze as well as releasing the alkaline ion like calcium as a constructed element of the glaze. In the forth sample from Safavid period in addition to the silica and quartz, cesterite phase represnt SnO2 which functioned as a flatting element in the glaze. In the fifth sample dated back to the 14-15 A.D, in addition to silica and quartz phases, nepheline synenite was reported because of the slip. 
Based on the EDX analyses, copper functioned as the primary element for making the turquoise color. The amount of the copper in the samples is respectively 3/19%, 1/15%, 3/53%, 1/39% and 1/36%.  The glazes have an alkaline base since sodium, potassium, calsium, mangesium and stroncium was reported in EDX analyses; This means that the samples of this research have an alkaline base unless the sample four. The amount of lead in the samples respectively is 13%, 0/17%, 0/27% and 12/64%; this element was not reported in sample five. Comparing to the other samples, sample four shows a great amount of lead (12/64%), and also have 7/07% amount of tin. Calsium solfate was reported in the samples; the amount of this element is respectively 4/06%, 2/35%, 2/75%, 3/72% and 2/67% which mostly is as a result of the destruction during the decades. The first sample represents the most amount of the calsium solfate comparing  to the other samples. The aluminum is respectively 4/06%, 2/25%, 2/75%, 3/72% and 2/67% which indicates the destruction during time. The most amount of destruction belongs to sample one and then sample four and is almost equal in the other samples.
   
Conclusion
In Iran, the most ancient usage of glaze has been reported from the ancient site of Susa as well as Choghazanbil located in the southwestern part of country in Khuzestan province. In the Achaemenid period application of glaze on mud-brick of royal buildings was one the common architectural decoration methods. In Islamic period, decoration using the glaze was widespread since it can be seen in buildings namely masques, schools along with potteries. In general, the Islamic potteries can be divided into two distinct groups: glazed and unglazed potteries. In this article, five turquoise glazed pottery sherds have been studied in order to identify their elements, composition and technology. The mentioned sherds dated back to 14 - 18 A.D (late Ilkhanate, Timurid and Safavid periods), and identified from a historical house called Moravvej-e Ardabili House, in the historical part of Ardabil city. EDX analyses indicated that the copper is the main element which used for creating the turquoise color. It is respectively from sample one to five,  3/19%, 1/15%, 3/53%, 1/39% and 1/63% in the samples and shows that sample three have the most amount of the copper in the glaze. In addition to this, chromium has been used as a coloring oxide in this sample. chromium in the glazes is a key factor in order to making the different shades of green color and this is why the color of this sample is much more different than the other samples. Based on the analyses, glazes have an alkaline base as a result of  high amount of the alkaline elements such as potassium, sodium and calcium in all samples. The amount of lead compare to the alkaline elements is a negligible amount unless sample four which a considerable amount of lead (12/64%) was reported; The amount of lead is respectively from sample one to four, 13%, 0/17%, 0/27% and 12/64%;This element was not reported in sample five. Also, in sample five, nepheline syenite indicates using slip on the pottery. Regarding the statistical analyses, generally there is a signnificant correlation between the samples. The high amount of the correlation is in samples two and five dated back to 14-15 A.D as well as the less correlation is between sample four dated back to the Safavid period and sample five belongs to 14-15 A.D which is seems resonnable.

Acknowledgment
We are thankful of MS Nasim Feizi for her technical point of view in the statistical study in this article and also, Miss Habibeh Abbasi for her beneficial comments.