Interpreting the Chemical Variability of Iron Smelting Slag: A Case Study from Northeastern Madagascar

Morel, Mélissa; Serneels, Vincent

doi:10.3390/min11080900

Cited by 9 publications

(9 citation statements)

References 21 publications

(21 reference statements)

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“…Over time, more than 20 quarries were reported (Verin, 1986), and even more have been visited in the course of this project. The Rasikajy were also actively involved in the smelting and forging of iron 2 and even though the production was small and catered only to limited local demands, over thirty slag heaps have been found (Morel and Serneels, 2021;Serneels et al, 2021).…”

Section: Archaeological Overviewmentioning

confidence: 99%

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The exploitation, processing and use of softstone in northern Madagascar and its links to the Indian Ocean world, 800–1500 CE

Nitsche

2023

Azania: Archaeological Research in Africa

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From the 9 th to the 16 th century CE, northern Madagascar was settled by the Islamised Rasikajy population who, as active participants in the Indian Ocean Trade Network, quickly started exploiting the various natural resources of the island. Among the most spectacular remains of the Rasikajy are finely decorated lathe-turned tripod vessels made from a particular dark green to gray silicate softstone called chlorite schist, that crops out in the crystalline hinterland. In the course of this project, over 30 quarries were visited, many of them previously unknown. The survey allowed a detailed look into the production line and operation of the quarries, which is very similar throughout the sites. However, local differences were still observed and suggest that while the vessel production followed a common technological tradition, it can not be considered as a standardised procedure. A unique feature of the production line is the use of an iron bar for the shaping of preforms, which has not been recorded elsewhere in the world and highlights the particularity of this Malagasy tradition.The petrographic study on a vast array of quarry samples and geological material with petrographic microscopy, X-ray fluorescence and X-ray diffraction allowed the characterisation of the material. Chlorite schist, a faulty petrographic name for a type of rock which should be called Hoesbachite or Amphibole-Talc-Chlorite Fels after modern standards, is a unique metacumulate that was metasomatised into an amphibole-and talc-rich softstone, which occurs in a single geological unit called Manambato Suite. Zircon dating revealed an emplacement age between 750-700 Ma for the quarried occurrences and recorded Pan-African metamorphism around 500 Ma ago. The metasomatic processes responsible for the formation of chlorite schist resulted in a high compositional variation that can occur on a quarry scale. Rasikajy workers were aware of this and ensured their specific material choice by testing the rocks in the quarries, resulting in a homogenous compositional array for the material used for vessel production. The detailed geological processes behind the compositional variation on a quarry scale are also crucial for other, more commonly used softstones such as steatites, and should be considered for any provenance attempt on these materials.In an attempt to refine the knowledge on the styles and particularities of the finished vessels, different stylistic groups were distinguished for the first time. In addition to the remarkable tripod vessels that were produced in the studied quarries, a second group of feet-less bowls made from talc schist was identified. This group, which was most likely produced in a second and older quarry zone south of the Bay of Antongil, is a rare find in the Malagasy archaeological record, but dominates the softstone inventory of Démbeni, an important trading port on ii Mayotte that was active in the late first millennium CE. The results from this study largely expand the history of softstone exploitation in northern Ma...

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Section: Archaeological Overviewmentioning

confidence: 99%

“…Despite these difficulties, collaborative research teams continue to try to advance Malagasy archaeology and document the country's rich history (e.g. Crossland, 2014;Radimilahy and Crossland, 2015;Douglass et al, 2019b;Morel and Serneels, 2021;Anderson, 2021;Serneels et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

The exploitation, processing and use of softstone in northern Madagascar and its links to the Indian Ocean world, 800–1500 CE

Nitsche

2023

Azania: Archaeological Research in Africa

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“…The high or low P 2 O 5 composition of the slag is mainly based on combustion nutrients (charcoal) used in the extraction process. Further, phosphorus is reduced under conditions very close to iron, and the decisive factor is that charcoal behaves as essential to reducing conditions during iron smelting (Craddock, 2000;Morel & Serneels, 2021). However, in crucible steel production, a minimal amount of dried wood is incorporated into the crucible, which does not remove the slag as it absorbs enough of the steel ingot (Juleff, 1996;Srinivasan & Ranganathan, 2004).…”

Section: Inter-element Relationship Of Slagsmentioning

confidence: 99%

“…However, in crucible steel production, a minimal amount of dried wood is incorporated into the crucible, which does not remove the slag as it absorbs enough of the steel ingot (Juleff, 1996;Srinivasan & Ranganathan, 2004). Charcoal contains about 5wt.% of ashes, including CaO (Morel & Serneels, 2021). Also, due to the reduction properties of CaO, re ning slags may contain a higher percentage of CaO than extraction slags.…”

Section: Inter-element Relationship Of Slagsmentioning

confidence: 99%

Ancient metalworking at Yodhawewa site, Sri Lanka: tracing the archaeological and geochemical relationship by analyzing soil and slags

Wijepala

Young

Ishiga

2022

Archaeol Anthropol Sci

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The Yodhawewa archaeometallurgical site was the latest discovery in Sri Lanka in 2018. This study aimed to trace the archaeological and geochemical relationship by analyzing the soil and slags of the site dating back to the c. 1st to 8th centuries AD. The analysis was mainly based on the X-ray uorescence (XRF) method. The soil chemistry resulted in some clues to special metal processing zones in the excavation-1 area. The cultural layers of that area (pro les 1 and 2) showed relatively high copper composition (max. 470ppm), and crucible fragments containing copper particles were also detected in the same layers. The vertical distribution of soil elements and their correlations with TiO 2 suggested that long-term metal activity may have affected changes in environmental soil chemistry. Relatively high phosphorus was indicated in the soil-related furnace wall, suggesting the arti cial addition of organic matter to the clay body during the furnace wall construction to withstand the high temperatures. High iron slag (HIS) varies from 12.96 to 49.63 wt% of Fe 2 O 3 and shows high MnO, P 2 O 5 , and V. Lightweight amorphous/glassy slags (LIS) associated with secondary re ning have low iron content and a high CaO and Sr composition.

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“…In particular, the chemical and mineralogical characterization of slags is a powerful tool for estimating key parameters of ancient iron and steel-making technology, such as temperature, oxygen fugacity of the reducing atmosphere, slag viscosity, and cooling rate. These parameters are intimately related to the efficiency of the reduction process and can give insight into the evolution of ancient technology [3,4]. It is worth mentioning that in Europe, starting from the first millennium BC until the 13th century AD, iron was exclusively produced by a one-step solid-state process (i.e., performed below the iron melting temperature at ~1200 • C) called the "direct" method [5].…”

Section: Introductionmentioning

confidence: 99%

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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Interpreting the Chemical Variability of Iron Smelting Slag: A Case Study from Northeastern Madagascar

Cited by 9 publications

References 21 publications

The exploitation, processing and use of softstone in northern Madagascar and its links to the Indian Ocean world, 800–1500 CE

The exploitation, processing and use of softstone in northern Madagascar and its links to the Indian Ocean world, 800–1500 CE

Ancient metalworking at Yodhawewa site, Sri Lanka: tracing the archaeological and geochemical relationship by analyzing soil and slags

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

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