Proceedings of the 39th International Symposium for Archaeometry, Leuven (2012) 086-090

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Chemical- mineralogical studies on iron crucibles from Chahak, Iran

M. Emami1,2, Z. Karamad3

1. Department of Conservation, Art University of Isfahan, PO Box: 1744, Isfahan, Iran 2. Department of Building Material Chemistry, University Siegen, Paul Bonatz St. 9-11, 57068 Siegen,

emami@chemie.uni-siegen.de 3. Faculty of Art and Architecture, Azad University of Shiraz, Iran,

zahra.karamad@gmail.com

ABSTRACT Crucible steel was the material used to produce famous sword and sabre blades, so-called “Watered or Damascus steel”. The method of production improves the physical properties of the metal. Crucible processes were used to make metals for different purposes and for swords in various locations in central Asia, India and Iran. One of these recently excavated areas is Chahak, in southwest Iran. According to historical manuscripts, Chahak has been an important crucible steel production site in Iran since the 11th century. An inspection of the site reveals hundreds of cylindrical crucibles, all of them fragmented. Some of them have massive slag cake remains inside. Surveying on the site shows slag heaps and scatters with different densities, shape and colour, these also include crucible lids and fragmented pottery. A chemical- mineralogical investigation was carried out on these objects. XRD, XRF and optical microscopy allowed an understanding of the extraxted material (mainly iron) at this site KEYWORDS Archaeometallurgy, Crucible, Iron technology, Chahak, Iran Introduction One of the great achievements of steel industries in the world is crucible steel. This method improves the manufacture of sword blades, daggers, knives, battle axes, broadswords and poniards. The main goal of this research is to highlight iron production in the Achaemenid period (550 – 331 BC) which is, as yet, unknown. In terms of the locations where crucibles were manufactured, different regions have been mentioned in historical texts and papers, such as central Asia, the Middle East and India (Caraddock 2000). Iran has been regarded as one of the biggest and most important centres for the arms industry in the far and near east since ancient times. So far, little scientific study has been conducted. The site of Chahak is located in the south west of Iran, in the eastern part of the Fars province, close to the Zagros main orogeny belt of pollymetallic ore outcrops. It is located in the northern area of the city Neiriz and the eastern part of

Arsanjan (Fig. 1). In old texts and manuscripts, the names Chahak, Neiriz and Arsanjan have been mentioned as important areas for mines and iron manufacturing in Fars and Iran. Based on geological surveys, economical copper and iron outcrops exist, some of which have a historic background close to the Chahak region (Emami and Yaghmai 2009). Ahmad Moghdasi in the first century (10 AD), in the book “The best divisions to know areas”, pointed out that “The soil of this region is enriched with economic minerals such as iron, magnesia, and emery” (Maghdasi 1983, in arabic). Maghdasi also writes, “Chahak in the northern part of Neiriz was important because of the nice steel, blades and swords which have been made from the local ore”. The blades made in Chahak are known as Chahaki Blades in the Islamic literature. Ibne Balkhi, another historian, in the book “Letter of Fars” in the 12th century wrote: “In Sahe [Chahak] iron and steel were used to manufacture blades and Chahak swords”. Concerning the centres for manufacturing swords and steel in Iran, Persian and Arabian historians mention that the area of Chahiq (=Chahak) was a famous centre for sword making and good blades called Chahigi. Even Ferdowsi, the great Iranian poet praises the quality and benefit of Chahigi blades (Moshtagh Khorasani 2006: 111). With respect to the literature review about the metallurgy in this region, the main road between Neiriz and Arsanjan in the 19th century was the main restricted zone for metal extraction and production. Hoseini Fasai in the book “Naseri letter of Fars” (in Persian) in the 13th century points out that Neirizi’s steel and economical ores were carried from mines located around 25km north of Neiriz (Fig. 2). Materials and methods The surface of the Chahak site is covered with pieces of crushed ceramics mainly earthenware and crucibles related to the smelting process. Furthermore, smelting slags are found on the site; so that the local people call this area “burned stone area”.

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Fig. 1. Location of Neiriz and Chahak in Fars province and their connection to Arsanjan and Shiraz.

Fig. 2. Elevation profile of direct path between mine locations.

Some typological examples were selected from different areas and their morphological features were investigated. According to the shape and archaeological context, the ceramic pieces are characterized chronologically as Achaemenid. No intact crucibles were found on this historical site; most of the crucibles were broken or were covered with a porous, molten material (Fig. 3, sample 69). The walls of the cylindrical crucibles of Chahak are about 13-15cm high, and their diameter is about 5-6cm, (although the diameter at the base of the crucible was smaller than that at the top). In addition, the body and the base of the crucibles are different in terms of thickness, colour and texture. Towards the base, the thickness of the body was 1-1.3cm and the thickness of the rest of the crucible was 0.5cm. The outer surface of most of the crucibles is covered with a dark coloured metal (in some cases greenish and in some cases reddish). Due to the reddish colour of these objects, the crucible seems to have been put in sand beds during the smelting process (Tylecote 1980).

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Fig. 3. Different kinds of crucible pieces found in Chahak through surface surveying. !Crucibles from other places show a honey-comb pattern on the inside (up to a height of 6cm), due to interaction with the slag (Feuerbach 2000). The crucibles are thicker in this area. The crucibles are covered with dark colours of slag on the external surfaces and they also have high porosity and a brittle texture (Fig. 3 sample 78 & 79). The changes in the structure and body of the crucible are illustrated in figure 3.

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The internal surface of some of the crucibles appears to have a textile pattern (or impression) (Fig. 3, sample 35); an indication of the crucible manufacturing process, in which sand in textile bags is used to mould them. The lower part of the crucible showed no traces of the textile pattern, possibly because the smelting process has removed all traces. Examples of these crucibles are also seen in the Akhsiket (Rehren and Papachristu 2000). In some other cases, the top internal surface is covered with a ball like mass of rust coloured steel. Examples of these are seen in the Marv crucibles (Feuerbach 2000). Mineralogical- chemical investigations were carried out by means of a characterisation of the textural as well as the chemical properties of the material. Polarization microscopy (LM) and environmental scanning electron microscopy (ESEM) were used. XRD including the Rietveld refining method was carried out to study crystalline phases. XRF was used for determination of the bulk chemical composition of the samples.

Results and discussion Bulk chemical composition of the samples The samples prepared for XRF analysis had different shapes and colours. These samples are illustrated and described in table 1 below. The samples are crucible pieces found on the surface during surveying. The results of major, minor and trace elements are illustrated in table 2. The crucibles are rich in iron oxide, while TiO2 could be coming from the ore material used, possibly enriched in ilmenite (FeTi2O4) (Emami and Yaghmai 2009). The very low amount of P2O5 proves that no phosphorous ore was used for metallurgy (Modarressi-Tehrani 2004). !Mineralogical investigation by XRD !The XRD analysis determined different crystalline phases, illustrated in table 3. Major crystalline phases in the matrix are: quartz, aluminosilicates and iron-oxides. Feldspars are among the minor phases. Cristobalite and Mullite also occur.

Table 1. Description of the samples investigated. Sample 37 Parts of the top of the crucible including slag Sample 44 Body of crucible with a slag-like layer in the

centre Sample 67 Crucible body with a honey-combed pattern Sample 68 Base of crucible Sample 8 Upper part of the body of a crucible

Table 2. Bulk chemical compositions of major, minor and trace elements in the samples in wt%.

Al2O3 SiO2 Fe2O3 Na2O P2O5 CaO MgO SO3 TiO2 K2O Cl MnO L.O.I

Sample 37 23.5 58.3 8.2 0.55 0.22 2.8 1.3 0.24 1.3 2.7 0.44 0.38 0.0

Sample 44 22.5 55.8 7.7 0.67 0.17 4.4 1.5 0.22 1.2 2.6 0.31 2.1 0.79

Sample 67 22.7 54.0 7.7 0.039 0.18 5.2 1.5 0.17 1.2 2.4 0.34 2.5 2.17

Sample 68 20.5 58.9 8.7 0 0.31 5.5 1.4 0.08 1.1 3.0 0.29 0.24 0.0

Sample 8 24.0 57.1 8.3 0.48 0.21 2.6 1.3 0.09 1.2 3.3 0.22 0.37 0.78

Table 3. XRD results of the qualitative crystalline phase constituents.

Amorphous

Phase Magnetite

Olivine Ag Feldspar Feldspar

(Ca) Cristobalite Quartz Iron Clay

Mineral Aluminium

Silicate Fe3O4 (K) SiO2 SiO2 Fe Sample

37 * * * *

Sample 44 * * * * * * *

Sample 67 * * * * * * * * *

Sample 68 * * * * * * * *

Sample 8 * * * * * * * *

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Mineralogical observation The samples were studied both on their base as well as the molten material (slag) on the external surface. According to the observations, the texture is very porous and glassy with products of high temperature smelting materials such as mullite (Fig. 6). The glassy matrices contain fayalite and iron rich phases as well as cristobalite (Fig. 7).

Fig. 6. Mullite crystals in the melt. !!!

Fig. 4. Diffractogram of one of the analyzed crucibles.

Fig. 5. Comparative illustration of all diffractograms.

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Fig. 7. Fayalite crystals in the glassy matrix. !Conclusion This study includes the qualitative and quantitative description of ancient crucibles found in south-central Iran. The samples are from the Chahak settlement (Achaemenid Period). Chahak is one of the reputed ancient sites which has been mostly cited in the old literature, but scientific work in this field is relatively recent. Scientific investigation of the crushed crucible finds, using qualitative and quantitative methods, provides useful data on the production technology of iron. Well rounded iron fragments observed in a few cases, are interpreted as the results of the reduction of iron oxide in the clay. Metallic iron is observed as tiny droplets in the siliceous rich parts, this is due to the reduction of iron oxides in the crucible during the smelting process. Fayalite was detected in the matrix of the slags and represented the iron rich silica melt. Wuestite was not detected in the texture and it proves a rapid cooling process of the metal in the crucible. According to the mineralogical as well as the chemical investigation, the crucible was used for iron extraction. Unfortunately, most crucibles are only metallurgically examined, not archaeologically, so that the potential for comparison is limited. A quite interesting point in the crucibles from Chahak is the huge deposition of these objects in the field, which suggests the importance of Chahak and the surrounding region as a technological periphery during the Achaemenid period. References Caraddock, P. 2000. From hearth to furnace: evidences for the

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