Assessing the Quality of Iron Ores for Bloomery Smelting: Laboratory Experiments

Abstract

There is fragmentary knowledge of iron ore sources exploited in the past for many regions including the Southern Levant. This missing information has the potential to shed light on political, economic, craft-production, and trading patterns of past societies. This paper presents the results of smelting experiments performed in graphite crucibles and a muffle furnace, using 14 iron ore samples from the Southern Levant, in an attempt to determine their suitability for smelting using ancient techniques. A range of analytical techniques, including optical and electron microscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction, and portable X-ray fluorescence were used to comparatively investigate the mineralogy and composition of the precursor iron ores and their smelting products: Iron bloom and slag. Several parameters attesting to the ability of a given ore to be successfully reduced and consolidated into a solid metal mass were quantified. The generated results highlight the significance of a 'correct balance' between iron oxides and other major elements in the smelting system in order to form fluid slag and a well-consolidated bloom. These data contribute to the understanding of factors, potentially influencing choices of iron ore exploitation by past human societies in the Southern Levant.The assaying (i.e., small-scale experimentation to determine quality of an ore) has always been an important component of ancient technology, as it represented an easy and resource-efficient technique to predict and coordinate subsequent large-scale processing and smelting [17]. For past societies, this was an advantage, given that properties of materials could be grasped only empirically and use of metallic resources was often associated with high resource and labor costs (e.g., extraction, transportation, and processing of the ore and fuel, cf. iron production in Africa [18]). The assay furnaces described by Agricolla [19] are a historical example of methods traditionally used for cupellation of small amounts of costly argentiferous ores to predict the outcome of large-scale cupellation performed in larger furnaces set to a greater consumption of raw materials.Determining the iron content and the quality of iron ores, prior to large-scale bloomery smelting, thus, is highly advantageous. Significantly, despite the common occurrence of iron ores in nature, knowledge about the types of deposits exploited in the past often remains limited and poorly understood. In fact, for some regions of the Ancient Near East, for example, south-eastern Arabia and Cyprus, there is still a lack of evidence about indigenous iron ore exploitation, although certain types of iron-rich rocks (e.g., gossans) exist in these regions [20][21][22][23]. Whereas in other regions, such as the southern Levant, evidence of past ore exploitation is only known so far from the Mugharet el-Wardeh deposit in the Ajloun, Jordan [5,24], although this is certainly not the only ore deposit in the region.In this paper, we present the results of a ser...

“A land whose stones are iron...”—Iron ore sources in the Southern Levant

“…Table 3 summarizes the major mineral components of the various ore deposits analyzed in this study. These are based on mineralogical characterization obtained by XRD and FTIR (some of which were previously published by Stepanov et al, 2020). Generally, the following minerals were identified: goethite and hematite as the major iron oxide phases and calcite, quartz, and occasionally barite and pyrite as secondary minerals.…”

“…Their mineralogy includes goethite as the main ore mineral that is occasionally intergrown with hematite. Based on previous XRD, FTIR, and scanning electron microscopy (SEM) analyses, quartz and calcite are the main associated non-metallic minerals, often in the form of lenses or veins, and small amounts of gypsum (CaSO 4 ) and barite (BaSO 4 ) are also commonly present (Stepanov et al, 2020). IP35 and IP36 were collected from a weathered yellow-ochre ore and show relatively lower iron oxide content of approximately 60 wt%, whereas the other samples (IP37-40) have iron oxide (Fe 2 O 3 ) content, which, on average, is higher than 85wt%.…”

“…Many of the Os isotopic ratio 187 Os/ 188 Os measured for the samples of the south Levantine sedimentary iron ores are within the variation range of sedimentary iron ores from southern Germany as presented in Dillmann et al (2017; Supplementary 2, Figure 7). This requires that Os isotope analysis, when applied to inter-regional trade of iron, will need to be combined with other chemical variables and will rely heavily on archaeological and historical considerations (Dillmann et al, 2017;Stepanov et al, 2023). For the Early Iron Age in Southern Levant, the possibility that iron was imported from Europe is doubtful, since, as mentioned previously, cultures there lingered behind in the adoption of iron technology (see Erb-Satullo, 2019).…”

Bloomery iron production in the Holy Cross Mountains (Poland) area during the Roman period: conditions during the metallurgical process and their uniformity between locations

“…In the case of many historical metallurgical centers, documentation describing the technical aspects of the metallurgical process is not available (e.g., [3][4][5]). Modern analytical methods based on determinations of the chemical and phase composition of metallurgical by-products, together with the use of experimental methods, allow to fill this gap by reconstructing the conditions under which the slags were formed and, thus, the conditions under which the smelting was carried out [6][7][8][9][10][11][12][13]. Since historical metallurgical processes often vary from location to location, there is no single path to follow during such archaeometric research.…”

Tradition and Innovation in Aegean Iron Technologies: A View From Early Iron Age Ionia

“… 9 When analysing a corroded object, the detection and interpretation of the so-called ghost structures, that is traces of carbon-rich structures in the fossilised background of the original internal structure, is crucial (Stepanov, Borodianskiy and Eliyahu-Behar 2020; Güder 2020; Verčík and Güder in preparation). …”