Jouttijärvi - The Shadow in the Smithy

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The Shadow in the Smithy

Arne Jouttijärvi aa Heimdal-Archaeometry, Virum, Denmark

Online Publication Date: 01 September 2009

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Jouttijärvi, Arne(2009)'The Shadow in the Smithy',Materials and Manufacturing Processes,24:9,975 — 980

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10.1080/10426910902987176

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Materials and Manufacturing Processes, 24: 975–980, 2009Copyright © Taylor & Francis Group, LLCISSN: 1042-6914 print/1532-2475 onlineDOI: 10.1080/10426910902987176

The Shadow in the Smithy

Arne Jouttijärvi

Heimdal-Archaeometry, Virum, Denmark

The work of a blacksmith leaves various kinds of debris. Well known are hearth-bottom slags, pieces of bloom, or forged iron and hammer-scale.Archaeologically, these materials can be used for identifying the remains of blacksmiths’ workshops. Detailed analysis of microscopic residuelike hammer-scale and slag spheres shows that they can be divided into different types corresponding to the different smithing processes such asbloom-consolidation, forming, welding, etc. It is, therefore, possible to identify the processes that took place in a given workshop. In a recentlyexcavated workshop dating to about 1020 [1], in successive years the floor was levelled out by the addition of a layer of sand that preserved theprevious layer of debris on the floor. Analyses of several hundred samples by combining archaeometallurgy, archaeobotany, and dendrochronologyhave yielded a detailed record of the use of the workshop until it was demolished in 1025. By mapping the spatial distribution of charcoal andmicroscopic debris like hammer-scale and slag spheres, it has proved possible to identify the position of an anvil, and by material dragged fromthis area, it is possible to trace paths made by the artisans when moving around the workshop. In one area close to the anvil the charcoal wascrushed, and the concentration of hammer-scale was low. This seems to represent the shadow of the blacksmith himself, crushing the charcoal ashe stands there with glowing hammer-scale deflected away from the anvil by his apron. A similar approach also can be used for less well-preservedworkshops.

Keywords Analysis; Blacksmith; Hammer-scale; Iron; Sampling; Slag.

On hammer-scale and slag spheres

The following is a brief outline of the conclusions drawnon basis of the examination and analyses of hammer-scaleand several hundred slag spheres from a number of differentiron smithing sites in Denmark and Norway.

The hot bloom, as it is extracted from the smeltingfurnace, will still hold quite a large amount of slag. Theslag at the surface will be knocked off as soon as the bloomis struck, but as much as possible of the rest of the slaghas to be removed by successive cycles of heating and

forging during the subsequent consolidation of the bloom.This refining process will give rise to the typical plano-convex slags often found in connection with remains of smelting or smithing activity. These slags will essentiallyhave the same composition as the smelting slag, apart froma tendency to a higher CaO, MgO, and K2O content due toreaction with charcoal ash in the hearth.

A simplified way to look at the analyses of slag, hammer-scale, and slag spheres is to look at the ratio of FeOto SiO2 and the total amount of K2O, MgO and perhapsCaO (Fig. 1). During the initial heating and forging of the slag filled bloom, slag droplets will be expelled fromthe iron, freezing in mid air as spheres, and solidified slagon the surface of the iron cracks into pieces of slag-scaleresembling hammer-scale, but thicker and more uneven instructure (mean thickness: approximately 700m). Thesespheres and slag-scale will have the same composition asthe internal slag.

Received August 12, 2008; Accepted April 2, 2009Address correspondence to Arne Jouttijärvi, Heimdal-

Archaeometry, Skovledet 30, Virum DK2830, Denmark; E-mail:[email protected]

As the amount of slag in the bloom gets smaller duringthe refining process, it cannot cover the entire surface ofthe iron and thereby protect it against oxidation. As theiron oxidizes, the oxides will react with the remaining slagat the surface, giving it a higher iron content than that ofthe slag-scale removed earlier (Fig. 2). The relatively smallamount of slag present will also dissolve oxides from thecharcoal ash, mainly K2O, CaO, and MgO. The scale formedat this stage is generally thinner than the slag-scale (meanthickness: app. 530m). When at last almost all of the slag

is removed from the iron, spheres and scales of molten slagcan no longer form. The refining process is now finished,the end product being a raw billet of consolidated iron, andfurther working of the iron will be the actual smithing ofartefacts.

At this stage, the iron surface is now exposed to hot air,and a thin layer of oxide will readily form. When the ironis forged, this layer will fall off as the well-known thin,even metallic bluish black-hammer scales. These scales willconsist mainly of magnetite, a magnetic form of iron oxide(>90%, Fig. 3), and have a relatively uniform thickness ofaround 100–300m. As iron oxide has too high a meltingpoint (around 1400C) spheres of this will not normally beformed.

The value of systematic sampling

When a site showing traces of smithing is excavated, fewif any samples of material from floors pits or postholes arenormally taken. A more systematic approach to samplingcan, however, be of great value, and in the present studyyielded much detailed information about the operationof the workshops. Three examples of excavations wheresystematic sampling was used is briefly described below.

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Figure 1.—Squares: slag; circles: slag spheres; triangles: slag scale.

Figure 2.—Towards the end of the cleaning, the slag spheres (circles) andhammer-scale (triangles) will absorb iron oxide.

Figure 3.—Hammer scale from smithing consists almost entirely of ironoxide.

Figure 4.—The excavation of the smithy at Klosterbakken. Postholes markedby flour.

Klosterbakken (Southern Jutland, Denmark)

The remains of a 13th century building (Fig. 4) wasidentified as a smithy by the slag found in the postholes,from each of which soil was sampled. The uppermost partof this building had been disturbed, and no trace of thefloor was left, and only the lowest part of the post-holes

remained. Pieces of vitrified clay most likely from thetuyeres were found in some of the samples, with relativelylarge concentrations found in connection with the remnantsof two almost square constructions, thought to be theremains of two forges (Fig. 5).

Concentrations of clay together with slag and other typesof waste were also found in the northeast and the southwestcorner of the workshop, indicating a nearby waste heap.Two types of hearth-bottom slags could be identified inthe workshop. The plano-convex refining slags seemed toconcentrate around the eastern forge (Fig. 6), and a smallnumber of smaller slags containing relatively large amountsof clay was found in connection with the western forge.

This seems to indicate a difference in the function of

the two forges. As might be expected, the slag-spheres andhammer-scale were concentrated around the centre of the

Figure 5.—Distribution of vitrified clay. Forges are marked by light greysquares, slag heaps by light grey circles.


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Figure 6.—Distribution of hearth-bottom slags. Dark grey: planoconvexrefining slags; grey: slag/clay mixture.

building, where two larger holes marked the locations of the anvils (Fig. 7).

Analysis of hammer-scale and slag-spheres showed,according to the previous discussion of different types,that material originating from cleaning of bloom dominatedaround the eastern forge and anvil, while traces of smithingwas primarily found around the western forge and anvil(Fig. 8). This confirms the different use of the two forges.

Apparently the somewhat smaller eastern forge wasalmost exclusively used for the consolidation of ironblooms, whilst the subsequent forging of knives and otherobjects took place on the western forge and anvil. Thecomposition of most of the slag found in the workshop,corresponded very well with the known smelting slags fromthe eastern part of Jutland, indicating that the iron used inthe smithy was probably of local origin.

Figure 7.—Distribution of hammer scale.

Figure 8.—The distribution of hammer-scale and slag spheres from bloomconsolidation (dark grey) and subsequent smithing (grey).

Rødbøl, Vestfold, Norway

Rødbøl is situated in the south-eastern part of Norway,and is tentatively dated to the Iron Age [2]. The structure of interest is an irregularly shaped dark layer partly covered bya rather large number of stones. Preliminary investigationssuggested that a layer containing hammer-scale and relateddebris could be the remains of smithing activity. Withinthe boundaries of the layer, a number of smaller pits andstructures identified as possible hearths were found. Samplesof the layer were taken at a spacing of 50 cm where possible,although initially only one sample from each square metrewas analyzed (Fig. 9).

The map in Fig. 10 shows the distribution of hammerscale

(dark grey spheres) and vitrified clay (light grey spheres).These materials, indicative of iron working, are found inthree or maybe four concentrations in the southern and

Figure 9.—Sampling of smithing remains from Rødbøl, Vestfold. Thesamples marked by dots were used for the first series of analyses; black:supposed hearths; grey: pits.


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Figure 10.—Distribution of hammerscale (dark grey spheres) and vitrified

clay (light grey spheres).

eastern part of the area, the area surrounding the presumedhearts showing very little sign of smithing activity. Slagfragments showed a similar distribution.

The concentrations of magnetic material, slag, charcoal,and vitrified clay indicated that a probable total of fourdifferent forges had been in use on this site. One of thesecould perhaps be identified in the southeastern corner of thearea (Fig. 11).

A charcoal-filled hollow was probably the remains of the hearth, and a large stone nearby, surrounded byhammerscale and slag-spheres could have served as anvil.

Figure 11.—Possible workshop. Hammerscale around the anvil marked bygrey spheres.

Because of the large number of stones deposited over thearea, the anvil stone was not recognized during excavation.

Viborg S øndersø , Jutland, Denmark

At Viborg Søndersø, in central Jutland, the very goodpreservation of organic material, due to [waterlogged]anaerobic conditions, allowed extensive and very detailedanalysis to be undertaken. Single context excavation

and extensive sampling for archaeometallurgical analysis,together with archaeobotany and dendrochronology, madeit possible to reconstruct the use of the workshop in detail.The building was erected in 1019 but was not equippedwith a raised hearth until the following year. Slag, charcoal,and vitrified clay in some of the earliest layers in thebuilding indicate that the workshop might at first have beena traditional Viking Age smithy with a ground level hearth inthe middle of the building. In the later winter of 1019–1920or early spring in 1020 this hearth was removed leaving agap which was filled in with sand. Some of the sand wasleft on the floor during the summer 1020, a period whenno activity took place in the workshop, as can be seen byweeds growing in the sand.

In the autumn of 1020 another layer of sand wasspread across the workshop, probably to level the floorbefore the installation of a raised hearth and the next

Figure 12.—Charcoal storage with diagonal “footpath.”


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period of use of the workshop during the autumn/winter1020–1021. Refining slags show that during this winterperiod the workshop was used for the consolidation of iron blooms, probably imported from Southern Germanyor central Europe. A large concentration of charcoal in thesouthwestern corner of the workshop is likely to mark theposition of a square booth used for storing this fuel (Fig. 12).

A diagonal “footpath” within this booth is marked by

crushed charcoal and an elevated concentration of magneticmaterial dragged here from the vicinity of the anvil by thewalking of the craftsmen (Fig. 13).

A concentration of corroded iron fragments in the south-eastern corner of the booth indicates the presence of a boxor barrel used for storing iron. The presence of cruciblefragments show that the workshop also had been usedfor the casting of silver during this period. From time totime, the hearth had been cleaned or rebuilt, with wastedebris having been heaped in the southeastern corner of thebuilding before being dumped to the north of the building.Some time early in 1021, the craftsmen finished their workand left the workshop. As in the previous year, a uniformgrowth of weeds across the floor indicates the workshop

was not used during the summer and that it was left roofless.The roof was rebuilt before the next period of use during

Figure 13.—The “footpath” as seen in the distribution of hammer-scale andrelated magnetic waste material.

the autumn/winter of 1021–1022, although the layout andorganization of the workshop by that time had been changed.

The distribution of magnetic waste material and charcoalfragments indicates that a large box or chest was nowplaced in the south-western corner of the workshop. Asduring the previous season, iron blooms were worked andiron (and possibly steel) produced. Again some cruciblefragments show that silver casting was also carried out,

but other crucible fragments indicate that this was nowaccompanied by bronze casting. Numerous fragments ofantlers also indicate the presence of a comb-maker. Againthis period of activity came to a stop at some time in thespring of 1022, and the workshop was again left until later inthe autumn, but this time the door was not closed properly,allowing the wind to sweep in leaves, twigs, and catkinsthrough the open doorway, and for weeds to grow where itwas light enough. Stray animals, probably sheep or goats,also entered the building leaving small lumps of faeces.In the winter of 1022–1023, the workshop was again usedfor iron-working and silver and bronze casting. This seemsto have been the most intensive period of use, resultingin a layer of debris almost 7cm thick. This layer yieldedmuch information and, as it was preserved across the entirebuilding, it was possible to reconstruct a detailed picture of

Figure 14.—Distribution of hammer-scale from the winter 1022–1023. 1–2: “footpaths” in the workshop; the circle marking the “shadow” of theblacksmith.


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Figure 15.—Distribution of lead droplets.

the organization of the workshop during this period of use(Fig. 14).

As expected, hammer-scale and related magnetic wastematerial was concentrated around the anvil, but it was alsodragged to the north-western corner of the workshop bythe craftsman working the bellows (1 in Fig. 14), and alsotowards the southern end, which is interpreted as having

had an open gable and, therefore, to have been better lit (2in Fig. 14). The blacksmith himself shielded the floor wherehe stood, leaving a “shadow” in the distribution of hammerscale. The box or chest in the south-western corner probablyserved as a work-bench for work needing the daylight. Thiscould have been for the finishing of objects forged or cast atthe fire in the dark end of the workshop, or it could be othercrafts not needing the more intense heat of the hearth. One

of these crafts seems to have been lead-casting, as indicatedby the recovery of nearly 1.2 kg of irregular lead dropletsfrom this area (Fig. 15). The distribution of the lead dropletswas also irregular.

In the early 1023, the use of the workshop ceased forgood. During the following two years, the building wasapparently kept in good repair, but there was no signthat the blacksmith, the silversmith, or the bronze casterever returned. During this period, new sandlayers werespread on the floor several times. At some time in 1024,it seems that the roof was again removed, possibly havingcollapsed. Rainwater now affected the surface of the sandand washed pieces of charcoal down from the hearth. Finallythe workshop was pulled down, the sand from the final

hearth used for levelling the ground here, and a new buildingerected, probably during 1025. No workshop debris wasfound in this building, and it appears not to have been usedfor anything related to smithing or casting.

References

1. Jouttijärvi, A.; Thomsen, T.; Moltesen, A. The metal workshop.In Viborg Søndersø, Iversen, M.I., Robinson, D., Hjermind, J.,Christensen, C., Eds., 1018–1030. Arkæologi og naturvidenskabi et værkstedsområde fra vikingetid (=Jysk Arkæologisk SelskabsSkrifter 52). Hø jbjerg, 2005; 297–320.

2. Rønne, O. Lokalitet 27 Gnr. 2040 bnr. 2, Larvik kommune. In:L.E. Gjerpe (red): E18-prosjektet, Vestfold årsrapport 2006. Oslo,2007; s. 41–45.

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