Mineralogical Characterization of Slags from Oiola Site (Biscay) to Assess the Development in Bloomery Iron Smelting Technology from the Roman Period to the Early Middle Ages

Portillo-Blanco, Haizea; Zuluaga, María Cruz; Ortega, Luis Ángel; Alonso‐Olazabal, Ainhoa; Cepeda-Ocampo, Juanjo; Salcedo, Ana Martínez

doi:10.20944/preprints202001.0111.v1

2020

DOI: 10.20944/preprints202001.0111.v1

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Mineralogical Characterization of Slags from Oiola Site (Biscay) to Assess the Development in Bloomery Iron Smelting Technology from the Roman Period to the Early Middle Ages

Haizea Portillo-Blanco¹,

María Cruz Zuluaga²,

Luis Ángel Ortega³

et al.

Abstract: Oiola archeological site, located in the mining complex of La Arboleda (Biscay, North Spain) was an important iron smelting center from the Roman Period to the Early Middle Ages and even in more current times (19th-20th centuries). Tap-slags and some plano-convex slags were identified as smelting slags. Samples were analyzed by optical microscopy, X-ray powder diffraction, scanning electron microscopy coupled with electron-dispersive spectroscopy and Raman microspectroscopy to perform a mineralogical and textu… Show more

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Cited by 4 publications

References 27 publications

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Ancient Metallurgical Iron Slags—Chemical, Powder X-ray Diffraction and Mössbauer Spectroscopic Study

et al. 2023

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The production and trade of metals was the foundation of the economic wealth of many regions in the world, which makes the study of ancient metallurgical slags of primary importance. This type of study is relatively new for Bulgaria, where research in the field started in the late 1960s with chemical analysis of copper ore, slags, tools and finished goods from the ancient copper mine in the Ay-bunar area. Iron is one of the most commonly found elements in the earth’s crust and its deposits are widespread, including on Bulgaria’s territory. To this day, however, the study of iron slags from Bulgarian sites through chemical and phase analysis has almost never been explored. The application of these methods allows for the determination of the technology of the ancient metallurgical process. This study investigates iron slags from two Bulgarian archaeological sites, situated in close proximity to the Sarnevets hematite ore deposit, Sarnena Sredna Gora mountain. The ore bodies of the deposit outcrop on the earth’s surface and can be easily recognized due to the red coloring of the soil around them, which is a characteristic trait for finding iron deposits. In addition to the ancient mining activities in the region, proven by over 20 registered ancient mine workings, ancient metallurgical activities were established as well, as proven by the discovered slags. A sample from the hematite ore was studied along with the slags, so that the percentage of iron extracted during the metallurgical process can be determined. The samples were studied through X-ray fluorescence analysis, powder X-ray diffraction analysis, and Mössbauer spectroscopy. The obtained results show that the slags are of the “furnace bottom slags” type, which is a product of metallurgical activity achieved through bloomery technology. The temperature range of the furnaces was determined to be around 900–1100 °C. The reduction of iron was possible at such low temperatures due to the ore’s type—self-fluxing hematite ore. The percentage of iron extracted from the ore was calculated to be between 3.39% and 8.65%. Additionally, a relationship was established between the percentage of extracted iron, the Fe2+ content included in wüstite, and the viscosity index of the liquid slag. The acquired results are new to the archaeological studies conducted on Bulgaria’s territory and are a prerequisite for future interpretation and archaeological research.

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Ancient Metallurgical Iron Slags—Chemical, Powder X-ray Diffraction and Mössbauer Spectroscopic Study

et al. 2023

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Contribution of EBSD for the Microstructural Study of Archaeological Iron Alloy Artefacts from the Archaeological Site of Loiola (Biscay, Northern Spain)

Rémazeilles,

Zuluaga,

Portillo-Blanco

et al. 2024

Heritage

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Iron palaeometallurgy was carried out on three artefacts, classified as nails and excavated from the archaeological site of Loiola (La Arboleda, Biscay, northern Spain), to investigate Roman manufacturing techniques. Energy Dispersive Spectroscopy (EDS) coupled with Environmental Scanning Electron Microscopy (ESEM) and micro-Raman spectroscopy were used to obtain elemental composition and structural characterization of mineral phases. Metallurgical properties and crystallographic texture were studied by combining microscopic methods such as optical microscopy (OM), Electron Backscatter Diffraction realized in environmental mode (EBSD) and measurements of local Vickers microhardness. The three artefacts had different microstructures, distinguished by a large gradient of carbon content, although important segregations (inclusions) were observed in all of them. Two pearlite-rich artefacts showed a high density of structural defects (geometrically necessary dislocations and large crystallographic orientation gradients in pearlitic ferrite, curved pearlitic cementite) resulting from a high level of plastic deformation that occurred during the manufacturing process. The third artefact consisted of pure ferrite without structural defects. This one was clearly manufactured differently from the two others, so it probably had another functionality.

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Archaeometallurgical Characterization of Two Lombard Early Medieval Bloomery Slags from Ponte di Val Gabbia I Site (Northern Italy)

Merico

Faccoli

Corte

et al. 2023

Metals

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An archaeometallurgical characterization of two iron smelting tap slags recovered from the early medieval site of Ponte di Val Gabbia I (Brescia, northern Italy) was performed. The main goal was to infer from the slags the working conditions of the ancient bloomery furnace in terms of temperature and oxygen chemical potential. The petrology of both slags was investigated by light optical microscopy and scanning electron microscopy, while their chemical compositions were measured via scanning electron microscopy coupled with X-ray dispersive spectroscopy. High-resolution Raman micro-spectrometry was used to confirm the identification of the mineralogical phases. The software Rhyolite-MELTS was used to compute the liquidus temperatures of the two slags, which were found to be 1120 °C and 1146 °C. These temperatures approximate the working temperature of the bloomery furnace. A thermodynamic-based approach was adopted to estimate the redox conditions of the reducing atmosphere of the smelting furnace, revealing that the two slags formed in different redox environments. Specifically, the resulting oxygen chemical potentials were −382.61 kJ/mol and −243.80 kJ/mol at the liquidus temperatures of 1120 °C and 1146 °C, respectively.

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Mineralogical Characterization of Slags from Oiola Site (Biscay) to Assess the Development in Bloomery Iron Smelting Technology from the Roman Period to the Early Middle Ages

Cited by 4 publications

References 27 publications

Ancient Metallurgical Iron Slags—Chemical, Powder X-ray Diffraction and Mössbauer Spectroscopic Study

Ancient Metallurgical Iron Slags—Chemical, Powder X-ray Diffraction and Mössbauer Spectroscopic Study

Contribution of EBSD for the Microstructural Study of Archaeological Iron Alloy Artefacts from the Archaeological Site of Loiola (Biscay, Northern Spain)

Archaeometallurgical Characterization of Two Lombard Early Medieval Bloomery Slags from Ponte di Val Gabbia I Site (Northern Italy)

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