Fulford battlefied under threat

July 2015 dig

The Fulford Tapestry

Iron finds

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Ferrous materials and rusting

Much of the material produced on a battlefield is ferrous in nature. The article looks at the chemistry and metallurgy of iron.

Properties of iron

  • Iron is a lustrous, ductile, malleable, silver-grey metal ( group VIII of the periodic table.)
  • It is chemically active but forms stable compounds. Iron forms oxides, hydroxides, halides, acetates, carbonates, sulphides, nitrates, sulphates, and a number of complex ions.
  • Forms two series of compounds
    • Bivalent ferrous
    • Trivalent ferric
  • It is known to exist in four crystalline forms.
  • The most common is the alpha-form, which is stable below 770°C and has a body-centred cubic crystalline structure
  •  Iron is attracted by a magnet and is itself easily magnetized.
  • It is a good conductor of heat and electricity.

Natural Occurrence

Iron is an abundant element in the universe; it is found in many stars, including the sun. Iron is the fourth most abundant element in the earth’s crust, of which it constitutes about 5% by weight, and is believed to be the major component of the earth’s core.

Iron is found distributed in the soil and water in low concentration. It is not found as a metal in nature but as ores and minerals which are abundant. The removal of elemental iron from the environment was one of the preconditions for the development of life on earth.

Iron is biologically significant as a component of haemoglobin, a red oxygen-carrying pigment of the red blood cells.

Rust

Iron rusts readily in moist air, forming a complex mixture of compounds that is mostly a ferrous-ferric oxide with the composition Fe3O4. Left undisturbed, the rust bloom can grow to many times the size of the object. X-ray is the recognised way to discover what, if anything, remains inside a lump of rust.

Production and Refining

Iron ores are refined in the blast furnace. The product of the blast furnace is called pig iron and contains about 4% carbon and small amounts of manganese, silicon, phosphorus, and sulphur. About 95% of this iron is processed further to make steel, often by the open-hearth process or the Bessemer process, but more recently in the United States and other countries by the basic oxygen process or by an electric arc furnace. The balance is cast in sand moulds into blocks called pigs. It is further processed in iron foundries.

Cast Iron

Cast iron is made when pig iron is re-melted in furnaces and poured into moulds to make castings. It contains 2% to 6% carbon. Scrap iron or steel is often added to vary the composition. Cast iron is used extensively to make machine parts, engine cylinder blocks, stoves and pipes.

Cast or 'grey' iron is produced when iron in the mould is cooled slowly. Part of the carbon separates out in plates in the form of graphite but remains physically mixed in the iron. Grey iron is brittle but soft and easily machined. White cast iron is made by cooling the molten iron rapidly and is harder and more brittle. The carbon remains distributed throughout the iron as iron carbide, Fe3C.

A malleable cast iron can be made by annealing white iron castings in a special furnace. Some of the carbon separates and becomes finely divided in the iron. A ductile iron may be prepared by adding magnesium to the molten pig iron - When the iron is cast, the carbon forms tiny spherical nodules around the magnesium. Ductile iron is strong, shock resistant, and easily machined.

Wrought Iron

Wrought iron is commercially purified iron. Pig iron is refined in a converter and then poured into molten iron silicate slag. The resulting semisolid mass is passed between rollers that squeeze out most of the slag. The wrought iron has a fibrous structure with threads of slag running through it; it is tough, malleable, ductile, corrosion resistant, and melts only at high temperatures. It is used to make rivets, bolts, pipes, chains, and anchors, and is also used for ornamental ironwork.

Steel

Steel is an alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulphur, and manganese. Steelmaking involves the removal of these impurities followed by the addition of desirable alloying elements.

Steel was first made by cementation, a process of heating bars of iron with charcoal in a closed furnace so that the surface of the iron acquired a high carbon content. The crucible method, originally developed to remove the slag from cementation steel, melts iron and other substances together in a fire-clay and graphite crucible. The famous blades of former times were made by these techniques.

Types and Uses

Steel is often classified by its carbon content

  •  High-carbon steel is serviceable for dies and cutting tools because of its great hardness and brittleness
  •  Low- or medium-carbon steel is used for sheeting and structural forms because of its amenability to welding and tooling.
  •  Alloy steels, now most widely used, contain one or more other elements to give them specific qualities.
  • Nickel steel is the most widely used of the alloys; it is nonmagnetic and has the tensile properties of high-carbon steel without the brittleness. Nickel-chromium steel possesses a shock resistant quality that makes it suitable for armour plate.

Possible sources of the iron objects on the battlefield

It is not impossible to rule out the possibility that the concentrations of metal objects along Germany Beck are the result of some activity other than the battle. Three other explanations were investigated.

Bog Iron

Bog iron is produced from plants found in wet lands which concentrate ferrous salts that are found in the water. There are some bog iron production sites south of Market Weighton and north of the river Humber. This iron extraction started before the arrival of the Romans and continued into medieval times when the bog material was exhausted. It left a substantial deposit of slag.[i]

In one experiment, 7.6kg of bog ore was smelted and yielded a 1.7kg bloom of iron.[ii] This was worked into a 0.45kg bar. The procedure required 61kg of charcoal and produced 6.1kg of slag. These ratios depend on the quality of ore and the skills of the metalworkers. There is not sufficient by-product material to suggest that Fulford was even a short-term production site and certainly fails to explain why so many iron billets should have been abandoned at the site.

The lack of slag and no suggestion of suitable plants or the associated ferrous salts in the water make bog-iron an improbable source for the metal workings found at Fulford. Other long-term manufacture of iron using ore is not known in this area. The English Heritage manual suggests the following indicators:

“Usually large amounts of slag will be recovered, including tap slag or large slag blocks. The bases of furnaces and tapping pits sometimes survive. Hammerscale is often found, as the iron bloom was usually consolidated on the smelting site. There is sometimes later evidence for waterpower.”[iii]

The finds do not suggest that Germany Beck was a site of iron manufacture.

Nearby building work

Smithing hearths have been reported that can be associated with a nearby building project. The construction of a church or monastic buildings would probably require several smithies to produce the fixings required. No candidate building requiring so much smithing activity can be identified in the area.

One might also expect the craftsmen to carry away their tools and any surplus material when the project was completed so it is surprising that useful material was left in the location. The balance of the samples from the billets recovered from the surface does not suggest that the purpose was construction or domestic. One might explain away a few arrows and axe shapes but there are no brackets, ties or fixings that one would associate with a building project.

‘Town planning’

In the report on the finds associated with Coppergate and Bedern, it was noted that

“One can .. envisage a fairly abrupt change in the character of this particular part of the city at the end of the 10th century or the beginning of the 11th century these heat-using crafts were moved to some safer location away from the increasingly crowded streets and tenements”.[iv]

In the century before the time of the battle, metalworking was being carried out away from the city. Walmgate and Fishergate have both produced evidence of ‘industrial’ iron working. So, while not excluding the possibility that the remote location of Fulford was a metalworking site, it is suggested that because it is not associated with any buildings, Fulford was not a place to which the activity of metalworking was removed. Two other clues support this suggestion.

“By 12th century most properties owned by blacksmiths were in the suburbs or close to the city gates. One reason is thought to be the rise in shoeing of horses….”[v]

In the 19th century a smithy can be seen on the early maps near the ford. This might have been a good location to ply for trade from visitors needing new shoes for their horses. The locations that have been identified as hearths are near roads and do not lie on the outskirts of any known conurbation. With the possible exception of zone 2, the hearths are set in fields, not even adjacent to any recognised paths.

Dumping (translocation or night-soil disposal)

Throughout the project, experts were constantly cautioning that ‘night-soiling’ provides false trails and misleading locations. However, it was not possible to obtain any systematic study of this reported activity in a way that would enable this to be factored in. The professional caution has been interpreted as no more than a warning when dealing with surface objects that are not found within a context that can be fully investigated to provide relevance.

There might be reasons to dump slag but the logical place would be on trackways rather than in fields. In the 19th century, the linings of blast furnaces were broken up and spread on the land where their basic nature would help neutralise the acidic effect of manure. But there is no sensible explanation for dumping the iron billets or tools in these rather inaccessible locations identified as the metal-reprocessing sites.

The data that is available at present cannot exclude these explanations but the discussion above provided some of the reasons why they are not the interpretation of the finds that is presented here.


[i] Valley of the first iron masters, Peter Halkon Uni of Hull 1999

[ii] XP27, Smelting a phosphorous-rich bog ore in a low, non-slag tapping shaft furnace, Crew 1991

[iii] Centre for Archaeology Guidelines Archaeometallurgy (2001) Product Code XH20166

[iv]Patrick Ottaway and Nicola Rogers  The Archaeology of York Small Finds 17/15 Craft, Industry and Everyday Life. Page 2997 CAB/YAT 1902771265 2002

[v] ibid 2977

 

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Related sites Facebook  Twitter (@ helpsavefulford)        Visiting Fulford        Map York

There is a site devoted to saving the battlesite: The site has the story of the process that has allowed the site to be designated an access road to a Green Belt, floodplain housing estate.

And another website for the Fulford Tapestry that tells the story of the September 1066: This tells the story embroidered into the panels.

The author of the content is Chas Jones - fulfordthing@gmail.com  last updated June 2015

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