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Fig. 11. Variations in manganese concentration (as MnO) in the bloomery slags, with chronol- ogy. Within several of the bloomery sites, there is a large variation in the content of manga- nese in slag. There is also intra-site as well as inter-site variation within the same chronological periods. In Motala the variation is more limited. http://files.webb.uu.se/uploader/1338/Fig11.jpe

Figure 11 Variations in manganese concentration (as MnO) in the bloomery slags, with chronol- ogy. Within several of the bloomery sites, there is a large variation in the content of manga- nese in slag. There is also intra-site as well as inter-site variation within the same chronological periods. In Motala the variation is more limited. http://files.webb.uu.se/uploader/1338/Fig11.jpe

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By Who, for Whom? Landscape, Process and Economy in the Bloomery Iron Production AD 400-1000 Eva Hjarthner-Holdar, Lena Grandin’, Katrina Skéld & Andreas Svensson
By Who, for Whom? Landscape, Process and Economy in the Bloomery Iron Production AD 400-1000 Eva Hjarthner-Holdar, Lena Grandin’, Katrina Skéld & Andreas Svensson
Table 1. Iron Age chronology referred to in the text. http:// files. webb.uu.se/uploader/1338/Table1.pdf In Sweden, bloomery iron production started already in the middle Bronze Age, often occurring in the same contexts as small scale bronze casting. Today, approximately 40 Late Bronze Age iron production sites are known (Hjarthner Holdar 1993). During the latter part of the Late Bronze Age, iron production sites started to appear in locations characterised as outlying areas far away from settlements and burial sites. Examples of such areas can be found in areas like Réda Jorden (the Red Soil) in the province of Vastmanland, and in northern Uppland. ‘This was evidently a period for prospecting, when people searched fo rich ore in the form of various types of limonite ore, but also places with plenty of fuel (cf. Grandin & Hjarthner-Holdar 2000; Grandin et al. 2000; Forenius et al. 2014b). The reason for the prospecting may be an increased demand for iron. Subsequently, during the Pre-Roman Iron Age (Table 1), perhaps as early as the eighth century BC, the production of iron had become so prominent that we can no longer speak only of production for self-sufficiency; there woul also have been a surplus production.
Table 1. Iron Age chronology referred to in the text. http:// files. webb.uu.se/uploader/1338/Table1.pdf In Sweden, bloomery iron production started already in the middle Bronze Age, often occurring in the same contexts as small scale bronze casting. Today, approximately 40 Late Bronze Age iron production sites are known (Hjarthner Holdar 1993). During the latter part of the Late Bronze Age, iron production sites started to appear in locations characterised as outlying areas far away from settlements and burial sites. Examples of such areas can be found in areas like Réda Jorden (the Red Soil) in the province of Vastmanland, and in northern Uppland. ‘This was evidently a period for prospecting, when people searched fo rich ore in the form of various types of limonite ore, but also places with plenty of fuel (cf. Grandin & Hjarthner-Holdar 2000; Grandin et al. 2000; Forenius et al. 2014b). The reason for the prospecting may be an increased demand for iron. Subsequently, during the Pre-Roman Iron Age (Table 1), perhaps as early as the eighth century BC, the production of iron had become so prominent that we can no longer speak only of production for self-sufficiency; there woul also have been a surplus production.
Fig. 1a. Excavated and reconstructed furnace for multiple firings with a slag-pit for the accu- mulation of slag underneath the shaft. Photo: Geoarchaeological Laboratory. Reconstructior drawing Svante Forenius, The Archaeologists. http:/ /files.webb.uu.se /uploader/1338/Fig1a-collagel000.jpe
Fig. 1a. Excavated and reconstructed furnace for multiple firings with a slag-pit for the accu- mulation of slag underneath the shaft. Photo: Geoarchaeological Laboratory. Reconstructior drawing Svante Forenius, The Archaeologists. http:/ /files.webb.uu.se /uploader/1338/Fig1a-collagel000.jpe
Fig. 1b. Excavated and reconstructed furnace for single use with a slag-pit for the accumula- tion of slag underneath the shaft. In the burnt clay, in the shaft, there are imprints that clearly demonstrate that the wattle was placed on the inside of the clay shaft, and not covered by clay. Reconstruction drawing Svante Forenius, The Archaeologists. http:/ / files.webb.uu.se /uploader/1338/Fig1b-collace1000.jpe
Fig. 1b. Excavated and reconstructed furnace for single use with a slag-pit for the accumula- tion of slag underneath the shaft. In the burnt clay, in the shaft, there are imprints that clearly demonstrate that the wattle was placed on the inside of the clay shaft, and not covered by clay. Reconstruction drawing Svante Forenius, The Archaeologists. http:/ / files.webb.uu.se /uploader/1338/Fig1b-collace1000.jpe
Fig. 1c. Excavated and reconstructed furnace for double blooms and slag tapping. Photo: Geo- archaeological Laboratory. Reconstruction drawing Lars-Erik Englund, The Archacologists. http://files.webb.uu.se/uploader/1338/Fig1ca.jpe http://files.webb.uu.se/uploader/1338/Fig1cb.jpg
Fig. 1c. Excavated and reconstructed furnace for double blooms and slag tapping. Photo: Geo- archaeological Laboratory. Reconstruction drawing Lars-Erik Englund, The Archacologists. http://files.webb.uu.se/uploader/1338/Fig1ca.jpe http://files.webb.uu.se/uploader/1338/Fig1cb.jpg
Table 2. Radiocarbon data from the 14C-analysed furnaces at the Motala site. Note that one furnace has two datings from the slag pit, one (Ua-30623) was charcoal from oak and the other (Ua-30624) from unspecified seed. Atmospheric data from Reimer et al. (2004); OxCal v. 3.10 Bronk Ramsey (2005);cub 1:5 sd:12 prob usp [chron]. http://files.webb.uu.se/uploader/1338/Table2.pdf
Table 2. Radiocarbon data from the 14C-analysed furnaces at the Motala site. Note that one furnace has two datings from the slag pit, one (Ua-30623) was charcoal from oak and the other (Ua-30624) from unspecified seed. Atmospheric data from Reimer et al. (2004); OxCal v. 3.10 Bronk Ramsey (2005);cub 1:5 sd:12 prob usp [chron]. http://files.webb.uu.se/uploader/1338/Table2.pdf
Fig. 2b. The excavated area at Verkstadsvagen in Motala. The picture shows the location of the furnaces, and other archaeological contexts related to the iron produc- tion site. The blue line marks the former shoreline and the red dots illustrate the dump zones with reduction slag. Graphics Katarina Skdld, The Archaeologists. http://files.webb.uu.se/uploader/1338/Fig2b.jpg Fig. 2a. Map of Motala, showing Lake Vattern to the west and Lake Boren to the east. The red dot marks the location of the iron production site on the north- ern shore of Motala Strom. Graphics Katarina Sk6ld, The Archaeologists. http: / /files.webb.uu.se/uploader /1338 /Fig2a.jpge
Fig. 2b. The excavated area at Verkstadsvagen in Motala. The picture shows the location of the furnaces, and other archaeological contexts related to the iron produc- tion site. The blue line marks the former shoreline and the red dots illustrate the dump zones with reduction slag. Graphics Katarina Skdld, The Archaeologists. http://files.webb.uu.se/uploader/1338/Fig2b.jpg Fig. 2a. Map of Motala, showing Lake Vattern to the west and Lake Boren to the east. The red dot marks the location of the iron production site on the north- ern shore of Motala Strom. Graphics Katarina Sk6ld, The Archaeologists. http: / /files.webb.uu.se/uploader /1338 /Fig2a.jpge
Fig. 4. Map of Osterg6tland based on Lantmiateriet’s General Map. Sites mentioned in the text are marked on the map. Farmland and flat land is marked in yellow; woodland is marked in grey-green. Graphics Katarina Skdld, The Archaeologists. http://files.webb.uu.se /uploader/1338/Fig4.jpg
Fig. 4. Map of Osterg6tland based on Lantmiateriet’s General Map. Sites mentioned in the text are marked on the map. Farmland and flat land is marked in yellow; woodland is marked in grey-green. Graphics Katarina Skdld, The Archaeologists. http://files.webb.uu.se /uploader/1338/Fig4.jpg
Fig.5. Gold bracteate from Vadstena. A bracteate produced from the same stamp was recov- ered in Motala. Photo: Ulf Bruxe SHM, bild-id 12931. http://files.webb.uu.se/uploader/1338/Fig5.jpe
Fig.5. Gold bracteate from Vadstena. A bracteate produced from the same stamp was recov- ered in Motala. Photo: Ulf Bruxe SHM, bild-id 12931. http://files.webb.uu.se/uploader/1338/Fig5.jpe
Fig. 6. A blacksmith’s hammer from the burial in Aska RAA 36. Photo: Helena Rosengren, SHM. http:/ /files.webb.uu.se/uploader/1338/Fie6.jpe
Fig. 6. A blacksmith’s hammer from the burial in Aska RAA 36. Photo: Helena Rosengren, SHM. http:/ /files.webb.uu.se/uploader/1338/Fie6.jpe
Fig 7. Map showing half of Sweden. The province borders are marked along with bloomery iron production sites mentioned in the text. Graphics Henrik Pihl, The Archaeologists. http://files.webb.uu.se/uploader/1338/Fig7.jpe
Fig 7. Map showing half of Sweden. The province borders are marked along with bloomery iron production sites mentioned in the text. Graphics Henrik Pihl, The Archaeologists. http://files.webb.uu.se/uploader/1338/Fig7.jpe
Fig. 9. Variation in bloomery furnace sizes (approximate inner diameter) with chronology. For the sake of simplicity, the chronology is indicated as exact years, but is in fact a time span with the selected date as the core value. Examples from Motala and three sites with a large number of furnaces, distributed over a period of time. The furnaces in Viby increased in size during the first hundred years. Later the size was relatively constant or reduced in the later furnaces. A similar situation is seen in Jarnstad and Horsas, covering a shorter time interval. The three fur- naces from Motala display the same pattern although the number is limited. http://files.webb.uu.se/uploader/1338/Fig9.jpg What does this observation about the size of the furnaces mean? Does it have anything to do with the efficiency of the process, or the product that was planned? ‘The efficiency of the furnaces has often been assessed rather schematically with the help of the bulk content of iron in the slag; the less iron (iron oxide) in the slag, the better process and more iron extracted. In part, thi: is valid, but in this context another component needs to be taken into account namely manganese. Manganese is an element chemically related to iron and is common in lake and bog iron ores. It can occur in concentrations of a tenth per cent or up to several tenths per cent, by weight. Variations in the content o manganese can be used to determine if iron ores of different compositions wer« used in the bloomery process. If there is a high content of manganese in the ore, there will also be a correspondingly high content in the slag, resulting in a lower content of iron, although this is misleadingly low if the efficiency of the process is to be determined. process is to be determined.
Fig. 9. Variation in bloomery furnace sizes (approximate inner diameter) with chronology. For the sake of simplicity, the chronology is indicated as exact years, but is in fact a time span with the selected date as the core value. Examples from Motala and three sites with a large number of furnaces, distributed over a period of time. The furnaces in Viby increased in size during the first hundred years. Later the size was relatively constant or reduced in the later furnaces. A similar situation is seen in Jarnstad and Horsas, covering a shorter time interval. The three fur- naces from Motala display the same pattern although the number is limited. http://files.webb.uu.se/uploader/1338/Fig9.jpg What does this observation about the size of the furnaces mean? Does it have anything to do with the efficiency of the process, or the product that was planned? ‘The efficiency of the furnaces has often been assessed rather schematically with the help of the bulk content of iron in the slag; the less iron (iron oxide) in the slag, the better process and more iron extracted. In part, thi: is valid, but in this context another component needs to be taken into account namely manganese. Manganese is an element chemically related to iron and is common in lake and bog iron ores. It can occur in concentrations of a tenth per cent or up to several tenths per cent, by weight. Variations in the content o manganese can be used to determine if iron ores of different compositions wer« used in the bloomery process. If there is a high content of manganese in the ore, there will also be a correspondingly high content in the slag, resulting in a lower content of iron, although this is misleadingly low if the efficiency of the process is to be determined. process is to be determined.
Fig. 10. Variation in bloomery furnace size (approximate inner diameter) with bloomery slags containing manganese (as MnO). Within several of the bloomery sites, there is a large variation in concentrations of manganese. In Motala, the variation is more limited. However, there is no correlation between furnace size and content of manganese. http: / /files.webb.uu.se/uploader /1338 /Fig10.jpg
Fig. 10. Variation in bloomery furnace size (approximate inner diameter) with bloomery slags containing manganese (as MnO). Within several of the bloomery sites, there is a large variation in concentrations of manganese. In Motala, the variation is more limited. However, there is no correlation between furnace size and content of manganese. http: / /files.webb.uu.se/uploader /1338 /Fig10.jpg
Related topics:
ArchaeologyPrehistoric ArchaeologyCommodity ChainsLate Iron Age (Archaeology)Scandinavian ArchaeologyPolitical Economy and Historyancient bloomery
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