Spinel-rich slag and slag inclusions from a bloomery smelting and smithing experiment with a sideritic ore
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Published
Sep 15, 2021
Abstract
This paper describes the scientific investigation of the raw materials, iron products, slags and slag inclusions from a bloomery smelting and bloom forging experiment. The smelt used a high alumina sideritic ore, a clay-built shaft furnace and a blowing rate of around 200 litres per minute. The smelting slag produced was viscous and frothy, most similar in composition, microstructure and morphology to slag from medieval bloomeries smelting similar ores. Unusually, the slag contained magnetite rather than the typical wüstite, in the form of dendrites which were often nucleated on euhedral spinel crystals. The distinctive microstructure and composition of the smelting slag allowed inclusions of this slag to be differentiated from others which were formed and modified during smithing from bloom to bar. The silica to alumina and the silica to lime ratios in the bloom and bar slag inclusions were lower
than in the smelting slag. A series of materials balance calculations indicates the influence of different proportions of furnace lining, fuel ash and ore on the smelting slags and the inclusions.
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References
Bellamy B, Jackson D and Johnston G 2001, ‘Early iron smelting in the Rockingham Forest Area: A survey of the evidence’, Northamptonshire Archaeology 29, 103–128.
Blakelock E, Martinón-Torres M, Veldhuijzen H A and Young T 2009, ‘Slag inclusions in iron objects and the quest for provenance: an experiment and a case study’, Journal of Archaeological Science 36, 1745–1757.
Bottinga Y and Weill D F 1972, ‘The viscosity of magmatic silicate liquids: a model for calculation’, American Journal of Science 272, 438–475.
Cleere H 1971, ‘Iron smelting experiments in a reconstructed Roman furnace’, Britannia 2, 203–217.
Crew P 1987, ‘Bryn y Castell hillfort – a late prehistoric ironworking in north-west Wales’, in B G Scott and H Cleere (eds), The crafts of the blacksmith (Belfast), 91–100.
Crew P 1989, ‘Excavations at Crawcwellt West, Merioneth, 1986–9: a late prehistoric upland iron-working settlement’, Archaeology in Wales 29, 11–16.
Crew P 1994, ‘Currency bars in Great Britain, typology and function’, in M Mangin (ed), La sidérurgie ancienne de L’Est de la France dans son contexte européen (Besançon), 345–351.
Crew P 1996, Bloom refining and smithing slags and other residues (London: HMS Archaeology Datasheet 6).
Crew P 2000, ‘The influence of clay and charcoal ash on bloomery slags’, in M Tizzoni and C Tizzoni (eds), Il ferro nelle Alpi – Iron in the Alps (Bienno), 38–48.
Crew P 2013, ‘Twenty–five years of bloomery experiments: perspectives and prospects’, in D Dungworth and R Doonan (eds), Accidental and experimental archaeometallurgy. Proceedings of the 2010 HMS annual conference (London), 25–50.
Crew P and Crew S 2001, ‘Excavations at Llwyn Du, Coed y Brenin, Merioneth, 2001: woodland management and charcoal processing
at a late 14th-century ironworks’, Archaeology in Wales 41, 83–87.
Dillmann P and L’Héritier M 2007, ‘Slag inclusion analyses for studying ferrous alloys employed in French medieval buildings: supply of materials and diffusion of smelting processes’, Journal of Archaeological Science 34, 1810–1823.
Dungworth D 2010, ‘The possible water-powered bloomery at Goscote (Rushall), Walsall, West Midlands’, Historical Metallurgy 44(1), 15–20.
Gordon R B 1997, ‘Process deduced from ironmaking wastes and artefacts’, Journal of Archaeological Science 24, 9–18.
Hedges R E M and Salter C J 1979, ‘Source determination of iron currency bars through analysis of the slag inclusions’, Archaeometry 21, 161–175.
Hollingworth S R and Taylor J H 1951, The Northampton Sand Ironstone: Stratigraphy, structure and reserves (London: Memoirs
of the Geological Society).
Høst-Madsen L and Buchwald V F 1999, ‘The characterisation and provenancing of ore, slag and iron from the Iron Age settlement at Snorup’, Historical Metallurgy 33(2), 57–67.
Ige A, Rehren T 2003, ‘Black sand and iron stone: iron smelting in Modakeke, Ife, south western Nigeria’, IAMS 23, 15–20.
Jackson D A 1982, ‘Great Oakley and other Iron Age sites in the Corby area’, Northamptonshire Archaeology 17, 3–23.
Jackson D A and Ambrose T M 1978, ‘Excavations at Wakerley, 1972–75’, Britannia 7, 115–242,
Morton G R and Wingrove J 1969, ‘The constitution of bloomery slags. Part 1: Roman’, Journal of the Iron and Steel Institute 207, 1556–1564.
Morton G R and Wingrove J 1972, ‘The constitution of bloomery slags. Part 2: Medieval’, Journal of the Iron and Steel Institute 210, 478–488.
Muralha V, Rehren T and Clark R 2011, ‘Characterization of an iron smelting slag from Zimbabwe by Raman microscopy and electron
beam analysis’, Journal of Raman Spectroscopy 42 (12), 2077–84.
Paynter S 2006, ‘Regional variations in bloomery smelting slag of the Iron Age and Roman-British Periods’, Archaeometry 48, 271–292.
Paynter S 2007, ‘Innovations in bloomery smelting in Iron Age and Romano-British England’, in S La Niece, D Hook and P Craddock (eds), Metals and mines. Studies in archaeometallurgy (London), 202–210.
Paynter S, Blakelock E and Hatton G 2012, Plas Tan y Bwlch, Snowdonia National Park, bloomery iron smelting – experimentation and archaeology (Swindon: unpublished English Heritage Research Report Series 25–2012).
Piaskowski J 1989, ‘Phosphorus in iron ore and slag, and in bloomery iron’, Archeomaterials 3, 47–59.
Pleiner R 2000, Iron in archaeology: The European bloomery smelters (Prague).
Rehren T, Charlton M, Chirikuri S, Humphris J, Ige A, Veldhuisen H A 2007, ‘Decisions set in slag: the human factor in African iron smelting’, in S La Niece, D Hook and P Craddock (eds) Metals and mines. Studies in archaeometallurgy (London), 211–218.
Taylor J H 1949. The Mezozoic Ironstones of England: Petrology of the Northampton Sand Ironstone formation (London: Memoirs of the Geological Survey).
Tholander E 1987, Experimental studies on early iron-making (Stockholm: Unpublished dissertation).
Thomas G R and Young T P 1999, ‘Bloomery furnace mass balances and efficiency’ in A M Pollard (ed), Geoarchaeology: exploration, environment, resources (London: Geological Survey of London Special Publication 65), 155–164.
Turner W E S 1956, ‘Studies in ancient glasses and glassmaking processes. Part V: Raw materials and melting processes’, Journal of the Society of Glass Technology 40, 277–300.
Turncock A C and Eugester H P 1962, ‘Fe-Al oxides: Phase relationships below 1000°C’, Journal of Petrology 3(3), 533–565.
Tylecote R F, Austin J N and Wraith A E 1971, ‘The mechanism of the bloomery process in shaft furnaces’, Journal of the Iron and
Steel Institute 209, 342–363.
Tylecote R F 1990, The prehistory of metallurgy in the British Isles (London).
Wolff von dr. E 1871, Aschen-analysen von landwirth-schaftlichen producten, fabrik-abfällen und wild-wachsenden pflanzen (Berlin).
Young T P 2011a, Archaeometallurgical residues from Ned’s Garden and Cindermill, Shropshire (unpublished GeoArch Report 2011/10).
Young T P 2011b, Archaeometallurgical residues from Little Furnace Wood, Mayfield, East Sussex (unpublished GeoArch Report 2011/21).
Young T P and Poyner D 2014, ‘Two medieval bloomery sites in Shropshire: the adoption of water-power for smelting’, Historical Metallurgy 46(2), 78–97.
Blakelock E, Martinón-Torres M, Veldhuijzen H A and Young T 2009, ‘Slag inclusions in iron objects and the quest for provenance: an experiment and a case study’, Journal of Archaeological Science 36, 1745–1757.
Bottinga Y and Weill D F 1972, ‘The viscosity of magmatic silicate liquids: a model for calculation’, American Journal of Science 272, 438–475.
Cleere H 1971, ‘Iron smelting experiments in a reconstructed Roman furnace’, Britannia 2, 203–217.
Crew P 1987, ‘Bryn y Castell hillfort – a late prehistoric ironworking in north-west Wales’, in B G Scott and H Cleere (eds), The crafts of the blacksmith (Belfast), 91–100.
Crew P 1989, ‘Excavations at Crawcwellt West, Merioneth, 1986–9: a late prehistoric upland iron-working settlement’, Archaeology in Wales 29, 11–16.
Crew P 1994, ‘Currency bars in Great Britain, typology and function’, in M Mangin (ed), La sidérurgie ancienne de L’Est de la France dans son contexte européen (Besançon), 345–351.
Crew P 1996, Bloom refining and smithing slags and other residues (London: HMS Archaeology Datasheet 6).
Crew P 2000, ‘The influence of clay and charcoal ash on bloomery slags’, in M Tizzoni and C Tizzoni (eds), Il ferro nelle Alpi – Iron in the Alps (Bienno), 38–48.
Crew P 2013, ‘Twenty–five years of bloomery experiments: perspectives and prospects’, in D Dungworth and R Doonan (eds), Accidental and experimental archaeometallurgy. Proceedings of the 2010 HMS annual conference (London), 25–50.
Crew P and Crew S 2001, ‘Excavations at Llwyn Du, Coed y Brenin, Merioneth, 2001: woodland management and charcoal processing
at a late 14th-century ironworks’, Archaeology in Wales 41, 83–87.
Dillmann P and L’Héritier M 2007, ‘Slag inclusion analyses for studying ferrous alloys employed in French medieval buildings: supply of materials and diffusion of smelting processes’, Journal of Archaeological Science 34, 1810–1823.
Dungworth D 2010, ‘The possible water-powered bloomery at Goscote (Rushall), Walsall, West Midlands’, Historical Metallurgy 44(1), 15–20.
Gordon R B 1997, ‘Process deduced from ironmaking wastes and artefacts’, Journal of Archaeological Science 24, 9–18.
Hedges R E M and Salter C J 1979, ‘Source determination of iron currency bars through analysis of the slag inclusions’, Archaeometry 21, 161–175.
Hollingworth S R and Taylor J H 1951, The Northampton Sand Ironstone: Stratigraphy, structure and reserves (London: Memoirs
of the Geological Society).
Høst-Madsen L and Buchwald V F 1999, ‘The characterisation and provenancing of ore, slag and iron from the Iron Age settlement at Snorup’, Historical Metallurgy 33(2), 57–67.
Ige A, Rehren T 2003, ‘Black sand and iron stone: iron smelting in Modakeke, Ife, south western Nigeria’, IAMS 23, 15–20.
Jackson D A 1982, ‘Great Oakley and other Iron Age sites in the Corby area’, Northamptonshire Archaeology 17, 3–23.
Jackson D A and Ambrose T M 1978, ‘Excavations at Wakerley, 1972–75’, Britannia 7, 115–242,
Morton G R and Wingrove J 1969, ‘The constitution of bloomery slags. Part 1: Roman’, Journal of the Iron and Steel Institute 207, 1556–1564.
Morton G R and Wingrove J 1972, ‘The constitution of bloomery slags. Part 2: Medieval’, Journal of the Iron and Steel Institute 210, 478–488.
Muralha V, Rehren T and Clark R 2011, ‘Characterization of an iron smelting slag from Zimbabwe by Raman microscopy and electron
beam analysis’, Journal of Raman Spectroscopy 42 (12), 2077–84.
Paynter S 2006, ‘Regional variations in bloomery smelting slag of the Iron Age and Roman-British Periods’, Archaeometry 48, 271–292.
Paynter S 2007, ‘Innovations in bloomery smelting in Iron Age and Romano-British England’, in S La Niece, D Hook and P Craddock (eds), Metals and mines. Studies in archaeometallurgy (London), 202–210.
Paynter S, Blakelock E and Hatton G 2012, Plas Tan y Bwlch, Snowdonia National Park, bloomery iron smelting – experimentation and archaeology (Swindon: unpublished English Heritage Research Report Series 25–2012).
Piaskowski J 1989, ‘Phosphorus in iron ore and slag, and in bloomery iron’, Archeomaterials 3, 47–59.
Pleiner R 2000, Iron in archaeology: The European bloomery smelters (Prague).
Rehren T, Charlton M, Chirikuri S, Humphris J, Ige A, Veldhuisen H A 2007, ‘Decisions set in slag: the human factor in African iron smelting’, in S La Niece, D Hook and P Craddock (eds) Metals and mines. Studies in archaeometallurgy (London), 211–218.
Taylor J H 1949. The Mezozoic Ironstones of England: Petrology of the Northampton Sand Ironstone formation (London: Memoirs of the Geological Survey).
Tholander E 1987, Experimental studies on early iron-making (Stockholm: Unpublished dissertation).
Thomas G R and Young T P 1999, ‘Bloomery furnace mass balances and efficiency’ in A M Pollard (ed), Geoarchaeology: exploration, environment, resources (London: Geological Survey of London Special Publication 65), 155–164.
Turner W E S 1956, ‘Studies in ancient glasses and glassmaking processes. Part V: Raw materials and melting processes’, Journal of the Society of Glass Technology 40, 277–300.
Turncock A C and Eugester H P 1962, ‘Fe-Al oxides: Phase relationships below 1000°C’, Journal of Petrology 3(3), 533–565.
Tylecote R F, Austin J N and Wraith A E 1971, ‘The mechanism of the bloomery process in shaft furnaces’, Journal of the Iron and
Steel Institute 209, 342–363.
Tylecote R F 1990, The prehistory of metallurgy in the British Isles (London).
Wolff von dr. E 1871, Aschen-analysen von landwirth-schaftlichen producten, fabrik-abfällen und wild-wachsenden pflanzen (Berlin).
Young T P 2011a, Archaeometallurgical residues from Ned’s Garden and Cindermill, Shropshire (unpublished GeoArch Report 2011/10).
Young T P 2011b, Archaeometallurgical residues from Little Furnace Wood, Mayfield, East Sussex (unpublished GeoArch Report 2011/21).
Young T P and Poyner D 2014, ‘Two medieval bloomery sites in Shropshire: the adoption of water-power for smelting’, Historical Metallurgy 46(2), 78–97.
How to Cite
Spinel-rich slag and slag inclusions from a bloomery smelting and smithing experiment with a sideritic ore. (2021). Historical Metallurgy, 49(2), 126-143. https://hmsjournal.org/index.php/home/article/view/68
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How to Cite
Spinel-rich slag and slag inclusions from a bloomery smelting and smithing experiment with a sideritic ore. (2021). Historical Metallurgy, 49(2), 126-143. https://hmsjournal.org/index.php/home/article/view/68