Rehren, T

Veldhuijzen, HA

English

UCL Discovery

34th INTERNATIONALSYMPOSIUM ONARCHAEOMETRY3-7 May 2004Zaragoza, SpainOrganising InstitutionsDepartment of Analytical ChemistryUniversity of Zaragoza, SpainPatrimoni-UB GroupUniversity of Barcelona, SpainCREDITS         PREFACE INDEX COLLABORATORS ARTICLESInstitución «Fernando el Católico» (C.S.I.C.)Excma. Diputación de ZaragozaZARAGOZA, 2006Maqueta symposium archaeome.  25/4/06  18:04  Página 1INDEX34th INTERNATIONALSYMPOSIUM245IRON SMELTING SLAG FORMATION AT TELLHAMMEH (AZ-ZARQA), JORDANXander VELDHUIJZEN and Thilo REHRENInstitute of Archaeology, University College London, United Kingdom1. ARCHAEOLOGICAL BACKGROUNDAt Tell Hammeh (az-Zarqa), Jordan, a wide range of metallurgical debrisfrom an early iron smelting operation (ca. 930 CalBC) was excavated (van derSteen 1997; van der Steen 1997; van der Steen 2001; van der Steen 2001; vander Steen 2001; van der Steen 2003; van der Steen 2003; van der Steen 2003;Veldhuijzen 1998; Veldhuijzen 1998; Veldhuijzen 1998; Veldhuijzen 2000;Veldhuijzen and van der Steen 1999; Veldhuijzen and van der Steen 1999;Veldhuijzen and van der Steen 2000). Tell Hammeh is a relatively small site innorthern Jordan, located where the Zarqa river valley opens into the JordanValley. It is close to several of the larger tells in this part of the Jordan Valleyas well as the main iron ore deposit of the wider region at Mugharet al-Warda(Abu-Ajamieh et al. 1988; Bender 1968).Several periods have been attested at the site, starting with Chalcolithic(ca. 4500-3000 BC) and Early Bronze Age (ca. 3000-2000 BC) material,followed by more substantial layers of Late Bronze Age (ca. 1600-1150 BC)material, to Iron Age I (ca. 1150-1000/900 BC) and Iron Age II (ca. 1000/900-586 BC) (van der Steen 2003).It is at the transition of Iron Age I and Iron Age II that metallurgicalactivity took place at the site. As iron production finds predating the Romanperiod are very rare in the Near East, Hammeh allows a unique insight intothe earliest developments of iron smelting technology in this region.2. THE IRON PRODUCTION PHASEThe large deposit of iron production debris at Hammeh forms astratigraphically well defined phase. It has a complex internal layering,possibly indicating seasonal activity over an extended period of time.Based on elevation levels of the remaining tell, half or more of theoriginal production area may have been lost due to bulldozer activity. LessMaqueta symposium archaeome.  27/3/06  16:20  Página 245than 7% of the projected production area has been excavated, yieldingroughly 500 kg of slag. The excavated area reveals no indication of domesticor non-metallurgical use of the site, nor of any distinct activity areas, exceptpossible furnace structures.Radiocarbon analysis of two charcoal samples (identified by Eleni Asoutias olive wood (Olea europaea), pers. comm.), provides a date at 930/910 CalBC (±40 years; 1 sigma ranges of 1000-900 and 940-850 Cal BC; AMS Analysiswith C13-C12 correction). With due caution (see: “van Strydonck et al. 1999),these dates place Hammeh among the earliest known finds of iron smeltingin the Near East (Pleiner 2000; Pleiner 2000; Pleiner 2000; Snodgrass 1980p.338; Waldbaum 1999). Taking these dates as a terminus post quem,production at Hammeh may cover a period from around 910 BC to ca. 800 BC. 3. CLASSIFICATIONInitial classification of the finds took place during excavation, based onmacroscopic features that can be observed in the field such as colour, shape,presence or absence of rust, flow patterns, and surface inclusions (Bachmann1982 p. 2-6; pers. comm.; Sperl 1980; Sperl 1980). This was examined furtherusing various laboratory techniques (Veldhuijzen and Rehren 2005). Several types of material were identified, the bulk consisting of slagand tuyère fragments. The slag types range from black/grey, free flowing slag(tap slag; ca. 50%), through less dense glassy slag (possible ceramic origin)and plano/concavo-convex slag-cakes (furnace bottom and possible primarysmithing) to rusty lumps (bloomery furnace mess; ca. 45%). The non-slagmaterial ranges from tuyère fragments (approx. 350) to charcoal and possiblefurnace structures. The tuyère fragments are characterised by a vitrifiednozzle and a 5 x 5 cm square section with a 1 cm bore (Veldhuijzen in press). 4. SLAG FORMATIONAAnalyses of the main type of slag demonstrate that clay is a majorcontributor to the slag formation in the Hammeh iron smelting process(Veldhuijzen 2003; See also: Serneels and Crew 1997; Crew 2000).Mass balance calculations, based on a haematite ore sample from Wardaand smelting tap slag from Hammeh (see table 1), indicate that 100 kg of orecontain theoretically enough wüstite (FeO) to enable the production of ca. 48kg metallic iron, while retaining 38 kg of slag of an iron oxide levelcomparable to the Hammeh slag. Other oxide components in this theoreticalslag, however, do not match the actual slag composition, particularly in theirlime content, which is too high, and alumina levels, which are too low. Theaddition of a further ca. 20 kg of local and tuyère clay to the system,34th INTERNATIONALSYMPOSIUM3-7 May 2004 • Zaragoza, Spain246 INDEXMaqueta symposium archaeome.  27/3/06  16:20  Página 246simulating the absorption of furnace wall and tuyère material, balances thetheoretical and archaeological slag composition much more closely. SiO2 Al2O3 FeO TiO2 MnO CaO MgO K2OP 2O5 SMugharet al-Warda Ore 8.50 0.38 82.32 0.07 0.05 8.29 0.15 0.03 0.21 0.00Local Clay/Tuyèreaverage (3 samples) 58.76 12.13 5.05 1.05 0.05 17.04 2.54 2.82 0.32 0.24Hammeh Tap Slagaverage (6 samples)  24.05 5.47 52.80 0.31 1.32 11.26 2.30 0.74 1.42 0.33Hypothetical slagceramic-free 22.98 1.03 52.20 0.18 0.15 22.39 0.41 0.09 0.56 0.00Hypothetical slag with ca 20 kg ceramic 26.31 3.65 52.37 0.36 0.08 15.19 0.86 0.77 0.35 0.06Table 1. Main components of Hammeh slag formation related materials (Warda ore, local clay and tuyèreceramic), actual Hammeh slag, hypothetical ceramic-free slag and hypothetical slag with ca. 20 kg of ceramiccontribution. Results are expressed in weight % and normalised to 100%. Samples were measured by (P)ED-XRF on Spectro XLab Pro 2000 with “Slag_fun” calibration method (Veldhuijzen 2003). See text for details onhypothetical slag composition.This addition though reduces the iron metal yield to ca. 33 kg, i.e. lessthan 2/3 of the amount calculated without the addition of ceramic. Whilethere is little doubt that a major ceramic contribution did in fact occur duringthe smelting operation, one wonders why the design in particular of thetuyères was done in such a way as to actually promote the absorption ofceramic material, which reduces the iron yield.5. DISCUSSIONOne possible explanation for this seemingly counter-productive featuremay be found in the relevant phase diagram CaO-FeO-SiO2 (see figure 1), andin particular in the morphology of the liquidus surface of this system.The hypothetical ceramic-free slag has been calculated to about 20 wt%SiO2, 50 wt% FeO and 20 wt% CaO; alumina being a major contributor to theremaining 10 wt%, but not exceeding 2 wt% on its own. Reducing such a slagto its three main components (or rather six, adding Al2O3 to SiO2, MnO to FeOand MgO to CaO) and plotting it into the phase diagram indicates a meltingtemperature in excess of 1250 °C, probably beyond the thermal ability of anearly furnace and the thermal refractority of the local clay.The addition of clay/ceramic to the system, in quantities of ca. 1/5 of theore weight, lowers the estimated liquidus temperature to around 1120 °C ifnot less, much more in line with the assumed performance characteristics of34th INTERNATIONALSYMPOSIUM3-7 May 2004 • Zaragoza, Spain247 INDEXMaqueta symposium archaeome.  27/3/06  16:20  Página 247INDEX34th INTERNATIONALSYMPOSIUM3-7 May 2004 • Zaragoza, Spain248an early furnace. This difference of ca. 100 °C makes the difference betweenthermal survival of the technical ceramic and fuel consumption and sufficientfluidity to allow the metal/slag separation to occur.ACKNOWLEDGEMENTSExcavations at Tell Hammeh (az-Zarqa) are part of the Deir cAlla RegionalProject, a joint undertaking of Leiden University (the Netherlands) andYarmouk University (Jordan) in conjunction with the Department ofAntiquities of Jordan.Figure 1. CaO-FeO-SiO2 Phase diagram. Plotted are six Hammeh tap slag (in green) and theiraverage composition (yellow), the local ore (red) and average local clay/ceramic composition(light blue), the hypothetical, ceramic free slag (dark blue) and the hypothetical slag when ca. 20kg of local ceramic is added to the system (purple) (for numerical values see table 1); values areplotted with MgO added to CaO, MnO added to FeO and Al2O3 added to SiO2.Maqueta symposium archaeome.  27/3/06  16:20  Página 248Study of the material is part of ongoing PhD research, carried out at theWolfson Archaeological Science Laboratories, Institute of Archaeology, UCL.It is sponsored by BHP Billiton through the Institute for Archaeo-Metallurgical Studies (IAMS).REFERENCESAbu-Ajamieh, M.M., Bender, F.K. and Eicher, R.N. 1988. Natural Resources in Jordan,Inventory-Evaluation-Development Program. Amman: Natural ResourcesAuthority .Bachmann, H.-G. 1982. The Identification of Slags from Archaeological Sites.Occasional Publication 6 London: Institute of Archaeology OccasionalPublication 6.Crew, P. 2000. The influence of clay and charcoal ash on bloomery slags. in Tizzoni,C.C. and Tizzoni, M., (Eds). 38-48.Pigott, V.C. (1999) The archaeometallurgy of the Asian Old World. Ephrata,Pennsylvania: University Museum, University of Pennsylvania.Pleiner, R. 2000. Iron In Archaeology. The European Bloomery Smelters. Praque:Archeologick_ Ústav Av Cr.Serneels, V. and Crew, P. 1997. Ore-slag relationships from experimentally smeltedbog-iron ore. in Crew, P. and Crew, S., (Eds). 78-82. Maentwrog: Plas Tan y BwlchOccasional Paper 3.Tizzoni, C.C. and Tizzoni, M. (2000) Il ferro nelle alpi. Giacimenti, miniere emetallurgia dall’ antichità al XVI secolo. Atti del convegno/Iron in the alps.Deposits, mines and metallurgy from antiquity to the XVI century. Proceedingsof the conference. Bienno: Commune di Bienno.van der Steen, E.J. 2001. Excavations at Tell el-Hammeh. Studies in the History andArchaeology of Jordan VII, 229-232.van der Steen, E.J. 2003. Tribes and Territories in Transition: the central East JordanValley and surrounding regions in the Late Bronze and Early Iron Ages: a studyof the sources. Groningen: Rijksuniversiteit Groningen.van Strydonck, M., Nelson, D.E., Crombé, P., Bronk Ramsey, C., Scott, E.M., van derPlicht, J. and Hedges, R.E.M. 1999. What’s in a 14C Date. Rapport du Groupe detravail : Les limites de méthode du carbone 14 appliquée à l’archéologie, 433-440.Rennes: Mémoires de la Société Préhistorique Française, XXVI, 1999 etSupplément 1999 de la Revue d’Archéométrie.Veldhuijzen, H.A. 1998. Early Iron Smelting. Analysis and Interpretation of Late IronAge Iron Smelting Remains from Tell Hammeh az-Zarqa, Jordan. Leiden: LeidenUniversity, Faculty of Archaeology, unpublished M.A. Thesis.Veldhuijzen, H.A. 2003. ‘Slag_Fun’ - ANew Tool for Archaeometallurgy: Developmentof an Analytical (P)ED-XRF Method for Iron-Rich Materials. PIA(Papers from theInstitute of Archaeology) 14, 102-118.Veldhuijzen, H.A. 2004 (in press). Technical Ceramics in Early Iron Smelting. The Roleof Ceramics in the Early First Millennium BC Iron Production at Tell Hammeh34th INTERNATIONALSYMPOSIUM3-7 May 2004 • Zaragoza, Spain249 INDEXMaqueta symposium archaeome.  27/3/06  16:20  Página 249(az-Zarqa), Jordan. In Proceedings of EMAC ‘03, (Ed.). Série Monográfica,Instituto Português de Arqueologia (IPA).Veldhuijzen, H.A. and Rehren, Th. 2005 (submitted). Early Evidence for Iron Smeltingin Jordan; how classification in the field relates to analyses in the laboratory.IAMS Journal 25. London: Institute for Archaeo-Metallurgical Studies.Veldhuijzen, H.A. and van der Steen, E.J. 1999. Iron Production Center Found in theJordan Valley. Near Eastern Archaeology 62 (3), 195-199.Waldbaum, J.C. 1999. The Coming of Iron in the Eastern Mediterranean. Thirty yearsof Archaeological and Technological Research. in Pigott, V.C., (Ed.). 16, 27-57.Philadelphia: MASCA, University Museum, University of Pennsylvania.34th INTERNATIONALSYMPOSIUM3-7 May 2004 • Zaragoza, Spain250 INDEXMaqueta symposium archaeome.  27/3/06  16:20  Página 250

(in press). Technical Ceramics in Early Iron Smelting. The Role of Ceramics in the Early First Millennium BC Iron Production at Tell Hammeh t h

(submitted). Early Evidence for Iron Smelting in Jordan; how classification in the field relates to analyses in the laboratory.

Early Iron Smelting. Analysis and Interpretation of Late Iron Age Iron Smelting Remains from Tell Hammeh az-Zarqa,

Il ferro nelle alpi. Giacimenti, miniere e metallurgia dall’ antichità al XVI secolo. Atti del convegno/Iron in the alps. Deposits, mines and metallurgy from antiquity to the XVI century.

Iron In Archaeology. The European Bloomery Smelters. Praque: Archeologick_ Ústav Av Cr.

Iron Production Center Found in the Jordan Valley.

Ore-slag relationships from experimentally smelted bog-iron ore.

Rennes: Mémoires de la Société Préhistorique Française, XXVI,

Slag_Fun’ - ANew Tool for Archaeometallurgy: Development of an Analytical (P)ED-XRF Method for Iron-Rich Materials. PIA(Papers from the

The archaeometallurgy of the Asian Old World.

The Coming of Iron in the Eastern Mediterranean. Thirty years of Archaeological and Technological Research.

The Identification of Slags from Archaeological Sites.

The influence of clay and charcoal ash on bloomery slags.

Tribes and Territories in Transition: the central East Jordan Valley and surrounding regions in the Late Bronze and Early Iron Ages: a study of the sources.

What’s in a 14C Date. Rapport du Groupe de travail : Les limites de méthode du carbone 14 appliquée à l’archéologie,

Iron Smelting Slag Formation at Tell Hammeh (Al-Zarqa), Jordan

Iron Smelting Slag Formation at Tell Hammeh (Al-Zarqa), Jordan

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UCL Discovery