The Archaeometric Study of 4th Millennium BCE Potteries from Tall-e-Eblis

Tall-e-Eblis, situated in southeastern Iran, is renowned as a significant prehistoric site. Joseph Caldwell initially conducted excavations at the site, and in 1964, further excavations revealed a remarkable amount of pottery related to the Aliabad culture. Surprisingly, this evidence remained untouched for years, stored in the National Museum of Iran’s archives. Consequently, we aim to rectify this by employing archaeometric methods to investigate these items. To accomplish this, a total of 10 Aliabad pottery from the Chalcolithic period were carefully selected and subjected to analysis using petrography, XRPD, and XRF techniques. The laboratory analyses have revealed diverse production techniques despite having a common origin. The soil utilized aligns with the geological outcrop of the area, indicating the extraction and utilization of soil mines and deposits surrounding Tall-e-Eblis. Furthermore, the examined potteries are categorized within the CaO+MgO-SiO2-Al2O3 system, ranging from high silica to high calcareous pottery. Samples and Methods Samples:Our samples consist of 10 pieces that were originally discovered by Caldwell in 1964 and belong to Tall-e-Eblis and the 4th millennium BCE. Specifically, the pottery being examined comes from level C of the stratigraphic layers, which contain cultural materials from the 4th millennium BC. The examined potteries show a variety of colors, ranging from buff ware to light pink, and are characterized by a thick layer of slip on its surface. It is important to note that the buff wares have higher porosity, while the pink-colored wares have lower porosity and greater strength compared to their buff-colored counterparts. 

 To conduct a mineralogical study and microscopic examination of the samples, as well as determine the technical characteristics of the pottery, thin sections (µ30) were created for each sample. This allowed for the use of an optical polarizing microscope, specifically the Camera Dp71, Olympusbx60, manufactured in Japan, to address this matter. XRPD analysis was utilized to identify and differentiate the crystalline phases present in the samples, and to ascertain the presence or absence of phases that may not be visible in thin sections. Consequently, a 0.5-gram sample was extracted from the desired pottery for analysis.The PHILIPS PW1730 diffractometer, manufactured in the Netherlands, was utilized to conduct the testing on the samples. The XRPD examination was carried out within the range of 10 to 60 degrees (2θ = 10-60). Additionally, the data was interpreted using the X'PertHighScore Plus software version 2008 (2.2.c). To determine the chemical composition of the samples, the XRF technique was employed with the PHILIPS PW1410 instrument, also manufactured in the Netherlands. Discussion Petrography:The pottery that was examined can be categorized into two primary groups based on their texture or fabric. Some samples possess a granule or silty texture, and some samples have a coarse or porphyry texture. The matrix of all the pieces is consistent and displays green or red colors, indicating the high temperatures that the pottery was subjected to during its production. A subset of the pottery exhibits an immature silty texture, with pieces of varying sizes placed next to each other, resulting in a somewhat disordered appearance. Despite their differences in size and quantity, all the pottery shares the same composition.       Quartz mineral is the most abundant component found in pottery, present in every sample. This mineral can be found in two forms: single crystal and polycrystalline. Among these forms, the single-crystal type is more prevalent. The angular to semi-rounded border of this mineral suggests that the quartz pieces were added to the primary source secondarily. The presence of polycrystalline quartz pieces in the texture indicates their origin from granitic and metamorphic sources, implying the use of soils from the studied area. Some of the studied samples exhibit a coarse texture, in which various fillers or tempers such as igneous rock, quartz mineral, plagioclase, sanidine, muscovite, biotite, amphibole, pyroxene, and pieces of chert and igneous rock have been incorporated.       Colloidal iron accumulation is evident in the samples, and in certain cases, high oxidation conditions have occurred, indicating the iron concentration on the surface of certain pebbles. The samples exhibit empty spaces and perfectly circular holes, suggesting the release of air bubbles from the pottery texture. These spaces do not show any signs of secondary calcite, indicating the presence of a minimal amount of moisture or carbon dioxide in the underground environment.        The pottery production shows the presence of Gerag and some samples exhibit visible sanidine grains, which align precisely with the mineralogical and characteristic traits of the Kerman region. In some samples, plagioclases undergo degradation and clay formation due to the Silicification process. Additionally, alkali-feldspars are discernible in two samples. Although apatite grains are present, they are found in minimal quantities. The majority of these samples lack calcite minerals, except for one sample where a small residue of calcite remains. Calcite mineral acts as a thermometer in the firing process. This mineral decomposes at a temperature of about 800 degrees Celsius and above, so it can be concluded that the firing temperature of pottery with calcite is lower than 850 degrees Celsius. Lime is one of the cases where the texture of pottery exists and shows itself as a secondary compound, and none of them have a crystalline state, which indicates a temperature higher than 850 degrees Celsius. Minerals of the mica group (muscovite and biotite) present in the texture of pottery have lost their optical properties in some cases. This property in these minerals can be considered as a thermal indicator because, at a temperature between 950-1000 °C, it loses its mineralogical optical property and turns from orange to yellow. XPRDAll Tall-e-Eblis potsherds exhibit a prominent and significant quartz phase in their spectra, which serves as a dominant indicator. The ratio of crystalline quartz phase to carbonate phases is evident in all samples, pointing towards their texture being rich in silica. In addition to quartz, feldspars are also commonly identified in the pottery's texture, with minerals such as orthoclase, microcline, albite, anorthite, plagioclase, sanidine, anorthoclase, and labradorite being present.       Hematite can be observed in two different forms within the texture of pottery. This particular mineral is formed either as a secondary mineral during the oxidation process at high temperatures in the furnace, resulting from the release of iron in muscovite at temperatures exceeding 950 degrees Celsius. Alternatively, it can also be formed as an oxide phase at lower temperatures, primarily as a product of the oxidation process in an underground condition (Maggetti & Schwab 1982). Pyroxene, on the other hand, is a secondary mineral that forms at high temperatures. Considering that this phase typically occurs at temperatures of 900 degrees Celsius and above, it can be inferred that the pottery has been subjected to significant heat. However, during the fourth millennium BC, pottery production had not yet reached a level of advancement where they could effectively control the firing temperature of pottery kilns to achieve proper firing. Therefore, it can be considered that their pottery production was more unconscious and based on their limited progress. Glenite, another high-temperature phase, has been identified in several ceramics. The comparative analysis of XRPD data from Tall-e-Eblis reveals that the phases of these potsherds fall within a similar range and exhibit structural similarities among them. XRFBased on the findings, there is a strong correlation among the potteries, indicating that the dispersion of silica oxide, calcium oxide, aluminum oxide, and trace amounts of rubidium, strontium, etc. fall within a specific and equal range. This data suggests that the potteries share the same correlation and can be categorized together. Specifically, these potteries are classified within the CaO+MgOSiO2-Al2O3 system, ranging from high silica to high calcareous clay. The silica to alumina ratio ranges from 3.9-4.4% by weight (w%), indicating a common source of clay. The MgO values, as a real value, range from 3.9-4.5% by weight, which suggests the presence of dolomite carbonate or calcite associated with high magnesium content in calcareous rocks. The loss on ignition (LOI) measurement, which indicates the lime content in the pottery, is not significantly high, implying that the lime content in these potteries’ matrices is relatively low. (Emami et al., 2016). In terms of the main chemical composition, the pottery from Tall-e-Eblis exhibits remarkable similarities. These similarities are particularly evident in the raw materials used, matrix processing, production processes, and baking temperature. Conclusion The petrographic analysis reveals that the observed quartz fragments exhibit angular and sharp edges, providing evidence of the use of mining and grinding additives in the dough. Most of the quartz has either a metamorphic or granitic origin. Additionally, other minerals such as plagioclase, feldspar, muscovite, biotite, and pebbles have been observed. These minerals can be related to the region's geological outcrops and share a similar origin and locality to some extent.        Based on the study of the Petro-fabric of the pottery with a red and green background, it can be inferred that the pottery has been subjected to high temperatures. This suggests that the potters during the Fourth millennium BCE were able to achieve relatively high temperatures in their kilns. However, it is important to note that the artisans of that period had not yet reached a level of development where they could precisely control the temperature and conditions of the kiln.        The pottery exhibits a relatively high porosity, which can be attributed to the high firing temperature and the decomposition of organic materials or polymorphic changes. Examination of the grain size and fillers in the pottery's texture reveals variations in the kneading process. Some pottery shows well-kneaded dough, while others lack proper kneading. High-temperature phases and grains are observed in certain potteries, allowing for an estimation of the approximate temperature at which the piece was fired. The suggested average temperature range is between 850-1000 degrees Celsius. Potteries with high-temperature phases in the range of 900-1000 degrees Celsius, without exceeding 1000 degrees, and potteries with low-temperature initial phases such as calcite in the range of 850 degrees Celsius are considered.        In conclusion, it can be stated that the soil used in the pottery dough was sourced from the same location. The difference in samples is only in their manufacturing technique, which the similarity of dendrograms and PCA also proves.