عنوان مقاله [English]
During the third millennium B.C., Shahr-i- Sokhta had a number of peripheral sites for the production of pottery. Among these, two sites including Rud-i-Biyaban 2 and Tepe Dasht are of most important Tepe Dasht, which is located at 3 km southwest of Shahr-i- Sokhta, had been a big manufacturing site for pottery production. Despite enough studies on the ceramic of Shahr-i-Sokhta, less research has been done on the type of fuel and the degree of temperature in the pottery kilns of the Sistan region during the Bronze Age. Therefore, the discovery of kiln at Tepe Dasht led us to two questions: 1) what was the fuel of pottery kilns at Tepe Dasht? 2) What degree was the temperature of the fuel provided? The hypotheses of the questions are as follows: 1) It was likely that wood and animal dung were used simultaneously as fuel for the kilns of Tepe Dasht. 2) It seems that wood and animal dung had probably provided temperatures between 600 and 900 ° C. The present study is done with the purpose of investigating the type of fuel and the amount of temperature of the pottery kilns of Tepe Dasht, in three ways: 1) Experimental Archaeology: constructing kilns with different sizes and shapes, measuring the temperature of the kilns by thermocouple and analyzing the present temperature and pressure of these kilns by Solid Works software. 2) Ethno Archaeological interview with residents of a number of villages in Sistan regarding animal dung and the way collecting and preparing animal dung as fuel in Sistani’s villages. 3) Laboratory analyses such as Performing XRF test on the samples of the modern dung ash heated in a laboratory with a temperature of 900 ° C and on the discovered ash from excavation of Tepe Dasht. The discovery of Cow figurines, animal dung residues and ash layers from Tepe Dasht may indicate use of animal dung as a suitable fuel for pottery kilns in this area. According to experimental analyses, the temperature produced by this type of fuel was between 600-900° C and even higher, which is an indicative sign of the proper quality of animal dung as fuel for ceramic production at Tepe Dasht.
Tepe Dasht and Rud-i-Biyaban 2 were among the ceramic production centers for Shahr-i- Sokhta (Mugavero, 2008: 3). However, Tepe Dasht with 5.5 hectares’ extent may had been one of the most important manufacturing site for ceramic production during the third millennium B.C. Nowadays, many kilns are visible on the site (Mortazavi, 2010: 11-12). Based on the wooden remains discovered from Shahr-i-Sokhta, a number of researchers have mentioned to the existence of a massive forest around the site. However, evidence for the above claim is absent. If the current natural environment of Sistan is considered in this research, we find that in the case of productiveness in lake environment, the main part of the vegetation of the region is straw; and the bushes of tamarisk, Haloxylon and Willow are commonly found in non-lake environments. Fire fuel based on the lake environment is not reliable due to quick ignition. The laboratory studies of Marzieh Kordan on the potteries discovered at Tepe Dasht indicate that the temperature was about 900 ° C in the kilns of the site. Therefore, the uncertainty associated with the fuel of the kilns of Tepe Dasht caused the authors to perform an experimental study in order to understand the type of the fuel of kilns at Tepe Dasht during Bronze Age. The purpose of this study is two folded, firstly to understand the type of the fuel used in the pottery kilns at Tepe Dasht; secondly to reconstruct the temperature of the pottery kilns at site based on experimental activities.
The discovery of the kilns at Tepe Dasht provides design of two basic questions:
1- What was the main the fuel of pottery kilns at Tepe Dasht?
2- How much was the temperature of the fuel at kilns of Tepe Dasht?
Regarding the above two questions, two hypotheses are raised as follow:
1- It was likely that wood and animal dung were used simultaneously as fuel at kilns of Tepe Dasht.
2- It seems that wood and animal dung used at ancient kilns of Tepe Dasht had probably provided temperatures between 600 and 900 ° C .
Experimental Archaeology at Tepe Dasht
The process of creating fire was carried out in several stages in kilns with different sizes and shapes by animal dung and wood.
Ethno-archaeological activities for preparing animal dung as fuel in Sistan Basin:
To have a better understanding of preparing process, eleven villages were selected as follow :1- Hassaniyan 2- Pol Asbi 3- Siyah Poshteh 4- Badil 5- Hossein Mosafer 6- Ghaleh Noo 7- Kaftargi 8- Yadegar 9- Mohammad Shahkaram 10- Deh Noo 11- Kohak.
Analysis of single-part kilns number 5 and 6 and two-part kiln number 7 by Solid Works software
The temperature and pressure in single-part kilns number 6 and 5 were higher at the reservoir than at other parts, due to the fact that there was a free air flow in the kiln tank.
The shape of the kiln number 7 was composed of two parts; the temperature at the reservoir was higher than the baking part. The reason for this is four folded: 1- The thickness and the surface material of the baking chamber; 2- outflowing a portion of the heat through the cavities preceding the baking chamber’s surface; 3- The height between the fuel reservoir and the baking place; 4- few number of cavities on the surface of the pottery baking chamber for transferring heat. The two-part kiln of number 7 did not show any significant change in terms of pressure.
The XRF test was used to analyze the elements in the ancient ash sample and the ash sample of modern animal dung.
The test indicates a significant amount of calcareous or calcium and alkaline compounds in the ancient ash sample (see CaO and K2O amounts in table 2). The remarkable difference between the amount of silica in samples and the almost identical amount of alumina indicates that there is more free silica in the modern ash sample. Free silica is related to plant species found in animal nutrition and ultimately to animal dung. The reason for the difference could be explained in the past and present biological conditions of Sistan Basin.
In response to the first questions of this study, what was the fuel of pottery kilns at Tepe Dasht? we can say that based on some brief evidence of the animal dung discovered around the kilns of Tepe Dasht, it seems that animal dung had been used as the primary source of fuel for the kilns at Tepe Dasht. The results of the ashes test are as follows: The ancient ash sample excels the modern ash in terms of the analysis of elements. The existence of calcareous compounds in the ancient ash sample suggests three possibilities:
1- Passing of time and soil being synthesized with ash residuals available near the kilns.
2- The presence of other fuels alongside animal dung.
3- The difference in the environment of Sistan in the third millennium BC with the modern environment of the region.
Question 2: What degree was the temperature of the fuel provided? It seems that both the animal dung and the wood had provided a temperature of 600-900° C for the kilns of Tepe Dasht. The results of the temperature test showed that the animal dung had cent rated heat and the temperature produced by dung and wood reached 1237 and 1314° C. In other words, these two fuels had also the ability to produce higher temperatures.