sign in sign up
<<
Home , Cementation process, Hammerscale

2001 01

Centre for Archaeology Guidelines Archaeometallurgy Archaeometallurgy is the study of metalworking structures, tools, waste products and finished metal artefacts, from the Bronze Age to the recent past. It can be used to identify and interpret metal working structures in the field and, during the post-excavation phases of a project, metal working waste products, such as slags, and moulds.The used in the past can be reconstructed from the information obtained. Scientific techniques are often used by archaeometallurgists, as they can provide additional information.

Archaeometallurgical investigations can provide evidence for both the nature and scale of mining, , refining and metalworking trades, and aid understanding of other structural and artefactual evidence.They can be crucial in understanding the economy of a site, the nature of the occupation, the technological capabilities of its occupants and their cultural affinities. In order that such evidence is used to its fullest, it is essential that Figure 1 Experimental working at Plas Tan y Bwlch: archaeometallurgy is considered at each stage of archaeological projects, removing an un-consolidated bloom from a furnace. and from their outset. (Photograph by David Starley)

These Guidelines aim to improve the its date and the nature of the occupation. For made use of stone tools or fire to weaken the retrieval of information about all aspects of example, archaeological evidence for mining rock (Craddock 1995, 31–7) and this can be metalworking from archaeological tin will only be observed in areas where tin distinguished from later working where iron investigations. They are written mainly for ores are found, iron working evidence is tools or explosives were used. curators and contractors within archaeology unusual before the beginning of the Iron in the UK and will help them to produce Age, and precious metal working is more Little is known about how ores were project briefs, project designs, assessments likely to be concentrated at high status and/or transformed into metals in Bronze Age and reports. urban sites. Britain. Neither smelting furnaces nor slags from the smelting of ores have been The Guidelines are divided into a number of The following chronological summary of the recovered from Bronze Age contexts in sections. First is a summary of the sort of archaeometallurgical record for the UK England (Craddock 1990; 1994), although metallurgical finds to expect on sites of all indicates the types of evidence that are likely some slag has recently been found on the dates (p 2-4). This is followed by a section to be found. Great Orme in North Wales (Jones 1999). entitled ‘Standards and good practice for archaeometallurgy’, outlining its relationship Bronze Age In the Bronze Age copper artefacts were with other aspects of archaeological projects Copper alloy and gold artefacts of this period produced by casting and smithing. Clay (p 4). Then come the fully illustrated show that these metals were worked. Some mould or fragments have been found sections describing archaeometallurgical evidence exists for copper mining, while on many Bronze Age occupation sites and a processes and finds: for iron (p 9), copper other evidence demonstrates working, mostly few have produced large quantities of these and its alloys (p 15), lead (p 18), silver and casting, of copper alloys. There is almost no objects, for example Dainton, Devon gold (p 19), tin (p20) and (p 21). A direct evidence for how other metals used (Needham 1980), Jarlshof, Shetland shorter section on non-metallurgical high during the Bronze Age were obtained. It is (Hamilton 1956) and Springfield Lyons, temperature processes illustrates finds that generally accepted that the tin ores in south- Essex (Buckley and Hedges 1987). However are often confused with metalworking debris west England were exploited from the Bronze finds of this type are rare in Early Bronze (p 21). A glossary of common metallurgical Age onwards but there is little direct evidence Age contexts. terms is provided (p 23). Finally come for this (Penhallurick 1997). sections introducing some of the scientific Some evidence for iron working has been techniques commonly used in Evidence for mining can only be expected in found in contexts that are culturally assigned archaeometallurgy (p 23) and a list of regions where ores are found. In England, to the Late Bronze Age. specialists who may be able to advise on copper ores are known in Cornwall, Devon, archaeometallurgical aspects of Shropshire, Staffordshire, Cheshire, North Iron Age archaeological projects (p 26). Yorkshire and Cumbria, and other sources Iron Age settlement sites generally provide are known in mid and north Wales more evidence for metalworking, and for a What to expect (Timberlake 1991). Old workings and wider range of metals, than Bronze Age sites. hammer stones (Pickin 1990) have been It is useful to know what sort of discovered during more recent mining and Iron ores, unlike copper ores, are found in archaeometallurgical evidence to expect from similar evidence has been recovered during many areas and iron mining and smelting a particular site. This depends on a number archaeological excavation of Bronze Age could be carried out on a small scale almost of factors, such as the location of the site, mining sites (Lewis 1990). Early working anywhere in Britain. No Iron Age iron mines

2 Archeo guidelines v10 hi res 28/6/02 11:45 am Page 3

are known, but bog ores and other surface of metalworking. These gradually developed structures and occupation layers have been outcrops were probably exploited. Only a few to incorporate some ‘Roman’ techniques. preserved, for example at Caerleon sites have so far yielded furnaces and large (Zienkiewicz 1993). Where workshop remains quantities of iron smelting slag, for example Roman are well preserved there is often evidence for Brooklands, Surrey (Hanworth and Tomlin A great variety of evidence for Roman a range of both ferrous and non-ferrous 1977), Welham Bridge,Yorkshire (Halkon and metalworking has been found throughout metalworking. Millett 1999) and Bryn y Castell and Britain. Any substantial excavation of a Crawcwellt, Gywnedd (Crew 1986; 1998). Roman period site is likely to recover The best known evidence for Roman lead some evidence. production consists of large inscribed lead Evidence for iron smithing is much more ingots, but some large litharge cakes, widespread, as at Dragonby, Lincolnshire Roman sites with large numbers of furnaces showing that silver was extracted from lead, (May 1996) and Scalloway, Shetland and huge quantities of iron smelting slag have have also been found in the Mendips and (Sharples 1999). Iron smithing can also be been discovered in the Weald of Kent and Welsh borders, for example at Pentrehyling indicated by cut fragments of iron stock and Sussex, for example at Bardown and Beauport (Bayley and Eckstein 1998). Small litharge hoards of ’ tools – for example at Park (Cleere 1974). Other major iron smelting cakes, produced during the extraction of silver Waltham Abbey, Essex (Manning 1991) – centres existed in the , from debased alloys, are also often found on while the microstructure of finished objects Northamptonshire and Lincolnshire but iron urban sites. provides information about the smiths’ smelting evidence has also recently been found techniques (Salter and Ehrenreich 1984). in other areas, such as at the Blackdown Hills, The only evidence for tin mining in the Important information on the use and trade Devon (Griffith and Weddell 1996), and can Roman period is the occasional inscribed of different types of iron stock can be be found almost anywhere. Iron smithing slags ingot. The casting of pewter is fairly well obtained from currency bars, for example the are routinely discovered on almost all Roman known from stone moulds that have been hoard found at Danebury, Hampshire sites, and occasionally blacksmiths’ workshops recovered from both urban and rural sites (Cunliffe 1984), and from more rare smithed are found, for example at Ashton, Northants (eg Blagg and Read 1977). blooms and billets. (Hadman and Upex 1975). Roman-period gold mining is known Most English Iron Age settlement sites have A number of large, circular, stamped copper from Dolaucothi, Dyfed (Burnham 1997). yielded some clay mould or crucible ingots have been found, particularly in Wales Parting vessels, for separating silver from fragments for casting copper alloys but a few (Kelly 1976), although no evidence of copper gold, have been found on a few urban sites sites, including Gussage All Saints, Dorset mines, furnaces or slag involved in their (Bayley 1991a). (Wainwright 1979) and Grimsby, production has yet been discovered. Lincolnshire (Foster 1995), have produced Specialised crucibles for production have Early medieval large assemblages. Coin manufacture can be been identified on a few urban sites (Bayley Both urban and rural settlements produce a demonstrated at a number of oppidum sites, 1984). Clay moulds and crucible fragments great variety of evidence for the working of such as Verulamium (St Albans), are relatively common finds on many Roman many different metals. The finds are not all the Hertfordshire (Frere 1983), and there was sites and occasionally the evidence is same in the different cultural areas of the possible silver production at Hengistbury particularly abundant, for example at British Isles (Bayley 1992c). Head, Dorset (Northover 1987). Castleford (Bayley and Budd 1998). Stone and metal moulds are also known, but are far A variety of iron smelting technologies, which Those parts of Britain that were not within less common. A number of workshops have produced distinctive types of slag, were in use. the Roman Empire kept Iron Age traditions been discovered in which a variety of Large slag blocks have been found at a number of sites, including Mucking, Essex and Aylesham, Norfolk (Tylecote 1986, fig 81), while at Ramsbury, Wiltshire (Haslam 1980) both non-tapping and tapping furnaces were found. Virtually every settlement site will produce at least small quantities of iron smithing slag and larger amounts are not uncommon, for example at Deer Park Farms, Antrim (Lynn and McDowell 1988) and Coppergate,York (McDonnell and Ottaway 1992). Metalworking tools are found, both in burials, for example at Tattershall Thorpe (Hinton 2000), and on settlements, for example at Coppergate (Ottaway 1992). The variety of manufacturing techniques employed by smiths increased and a much wider range of structures, including pattern-welding, are commonly seen in metallographic studies of iron artefacts.

The whole range of non-ferrous metals was Figure 2 Reconstruction of a Roman workshop, based on excavated features and finds from Verulamium. (Illustration by Michael Bayley) widely used (Bayley 1991b) and evidence for

3 refining, casting and smithing is common on Urban excavations frequently recover and experimental laboratories and many types of sites. Examples include urban evidence for secondary working of the whole workshops. Throughout the period their sites, such as Coppergate, York (Bayley range of metals (Bayley 1996). The scale of archaeology remains poorly understood, even 1992b) and Armagh (Gaskell Brown and metalworking increases in this period and the into the 20th century (Matthews 1999). Harper 1984), monastic sites, such as size of assemblages is often larger, although Recycling became more efficient in later Hartlepool, Tyne and Wear (Daniels 1988), the range of finds is similar to that of the early periods so quantities of finds are and some other high status centres, for medieval period. This change in scale is correspondingly reduced. example Dinas Powys (Alcock 1963) and particularly noticeable in crucibles whose size Dunadd (Youngs 1989). Typical finds are increases (Figure 23 and Bayley 1992a), and In the iron industry, blast furnaces, both small crucibles, cupels, litharge cakes, bar large clay moulds for castings such as -fuelled and (later) coke-fuelled, are ingots, and scrap and waste metal. Ingot- and cauldrons and bells became common well known archaeologically (Crossley 1990), object-moulds are made from stone, clay and (Richards 1993). Mass-production also led to but the finery-chafery forge and its later antler. Crucibles, scrap metal and clay changes in mould . Multi-part clay developments are less often identified. The moulds for small objects are common. moulds for casting dozens of objects at one few upstanding cementation furnaces time were developed (Armitage et al 1981) (Cranstone 1997) and crucible steelworks are Medieval and reusable limestone piece moulds were quite well known. furnaces dating From the medieval period onwards there was made for casting pewter trinkets (eg to this period have also been found, especially an increasing tendency for metal industries to Margeson 1993, fig 127). in more remote areas (Photos-Jones et al 1998). be concentrated in towns, and often in particular areas of towns, although iron Post-medieval As before, non-ferrous smelting is mainly smithing also took place in many rural During this period a wide range of both concentrated in areas near suitable ore settlements. Another exception was bell- ferrous and non-ferrous metalworking took sources. Slag scatters and patches of bare casting which was often, although not always, place, and technologies evolved rapidly, often polluted ground can indicate a bole hill lead- carried out where the bell was to be used with several complete changes in practice smelting site. Earthworks or ruins in ore-rich (Greene 1989). Smelting was still carried out within the period (Crossley 1990, Day and areas can indicate later smelting constructions, near the ore sources. Tylecote 1991). With the increasing whether for lead, copper or tin. separation of ‘industry’ from agricultural and Water power was being used to operate domestic life, many sites and field Archaeological interventions on ‘industrial bellows and trip hammers by the 12th century monuments become primarily industrial in archaeology’ sites usually concentrate on (Astill 1993) and its availability led to the function and can be immediately identified as surveys of above-ground buildings and development of the for iron such. This situation is less true, however, of features, but sampling of buried deposits can smelting from the end of the 15th century. craft workshops, small-scale urban industry, often clarify the uses to which the site was put.

Stages Archaeological Action Specialist Action Standards and good practice

Initiation Curator identifies need Respond to any request for input to brief for archaeometallurgy for project and produces brief This section sets out the relationship between Planning Contractor contacts Provide input to Project Design. Plan excavation archaeometallurgy and other aspects of specialist and sampling strategy for metalworking features archaeological projects. It also contains specific information, mostly drawn from Fieldwork Survey site/landscape Identify features located and estimate scale of medieval and earlier examples, addressed to activity all those who are likely to encounter Excavation Advise on identification of metalworking archaeometallurgical evidence. The principles features. Establish metalworking reference are the same when dealing with later sites, collection. Suggest sampling strategies. Advise on but the scale of the industry is sometimes cleaning and packaging far larger.

Assessment Provide information on Assess all (or a sub-set) of the finds in an metalworking features assemblage in the light of the archaeological Most archaeological projects are initiated and debris (spatial information.Write assessment report, which through the planning process when curators distribution and phasing) should include recommendations for further (county archaeologists, etc) identify the need work (including a methods statement and for work to be done. The principles they estimate of time/cost for analysis phase) follow are laid out in PPG16 in England (Department of the Environment 1990), Analysis Liaise with specialist(s) Undertake the work identified at the assessment stage. Identify metalworking processes and NPPG5 and PAN42 in Scotland (Scottish estimate scale of work. Quantify debris by Office 1994a and 1994b), Circular 60/96 in context, phase, area, etc Wales (Welsh Office 1996) and PPS6 in Northern Ireland (Department of the Dissemination Incorporate Write archaeometallurgical report(s) for Environment (NI) 1999). Having decided archaeometallurgical inclusion in excavation report and/or specialist reports into excavation publication that a site needs evaluation, the curator report produces a brief for the work and the contractors (archaeological units) then

4 respond with a written scheme of activities. The desk-based study should include Fieldwork: excavation investigation. Alternatively, work is sometimes any metalworking evidence from earlier Many kinds of metalworking structures and commissioned by a statutory body such as archaeological interventions, but past debris are distinctive in appearance, and with English Heritage, in which case the metalworking activity can also be suggested by experience or training these can be documentation is known as a project design. local geology, documentary evidence, place- recognised in the field. Early consultation In either case, a contractor is selected to names and even vegetation surveys (Brooks with a metalworking specialist and a site visit undertake the archaeological project. 1989; Buchanan 1992). There is rarely will enable the evidence to be better substantial evidence, however, for understood. The metalworking specialist can The successful completion of archaeological metalworking in urban areas before excavation. provide training, suggest appropriate projects depends on careful planning and sampling strategies, put together a site implementation, whether they are small Fieldwork: survey reference collection, and advise on cleaning watching briefs or more extensive Much can be learnt about metal working sites and packaging procedures. excavations. Large archaeological projects prior to, or in the absence of, excavation. normally pass through five phases (English Information is sometimes gained about the Heritage 1991; Historic Scotland 1996): types of processes carried out and the scale of the craft or industry. The survey • Project planning and the formulation of methodologies employed will depend, to a research design large extent, on the current land use. • Fieldwork • Assessment of potential for analysis Aerial photography is a relatively inexpensive • Analysis and report preparation means of characterising well-preserved • Dissemination industrial landscapes, such as mining and smelting features in upland regions that are Figure 4 Iron Age bloomery furnace at Crawcwellt West, Each phase of a project should have clear now under pasture (Gerrard 1997; 2000). Merioneth. (Photograph by Peter Crew) objectives, and these should be regularly Metric surveys can determine the extent of reviewed. This framework can be applied metalworking debris that survives as The three metalworking processes most likely beneficially to all archaeological projects, earthworks, and so indicate the scale of to be encountered by archaeologists during although formal reviews might not be metalworking activity. The interpretation of fieldwalking, evaluation and full scale appropriate for minor interventions. upstanding metalworking remains from either excavation are iron smithing, iron smelting Archaeometallurgy is an integral part of aerial photography or from metric survey and secondary non-ferrous metalworking, archaeological investigations and plans requires input from a specialist (Cranstone such as casting of copper, lead or precious should be made for its inclusion, even in 1994; Gerrard 1996; Starley 1999). metals. Additionally, in certain geological small-scale evaluations, where sites have areas the smelting of non-ferrous metals archaeometallurgical potential. An Geophysical survey, especially using magnetic might be encountered. experienced specialist can advise on an techniques, is often well suited to detecting the appropriate level of provision. remains of archaeometallurgical processes. The range of possible metalworking evidence Many slags (in particular iron smithing slags) can be divided into structures and finds. Project planning and the formulation have higher magnetic susceptibilities than Structures and features include mines, pits, of research designs topsoil. Both primary (smelting) and water channels, dams, buildings, furnaces Curators should be aware of the secondary (smithing) sites will have fired and hearths. Finds can include slags, ceramic archaeometallurgical potential of sites in their structures such as furnaces and hearths that materials, tools, stock metal and metal areas and should ensure that any briefs they can produce strong magnetic anomalies (see residues. The excavation of metal working draft require adequate investigation of these p 24 for further details). sites should include the examination of aspects of the archaeological record.

Given the frequency with which slags and other archaeometallurgical finds are discovered, contractors should approach appropriate specialists at the project planning stage. They can contribute to the research design and help to prepare an appropriate excavation and sampling strategy. If the site is thought to have been primarily metallurgical in function, then archaeometallurgy should be a major aim of the project design. Even when the metallurgical potential of a site is not thought to be large, some contact with a specialist is desirable, as small amounts of debris are not necessarily less important – and an initial contact will pay dividends when unexpected discoveries are made.

Prior to fieldwork, desk-based studies can indicate the likelihood of archaeometallurgical Figure 3 Earthwork survey of the Iron Age slag dumps at Sherracombe, Devon. (© Crown copyright. NMR)

5 associated features, such as domestic Secondary deposits are contemporary with or A workshop floor surface comprising a single dwellings, in order to place the technology in later than the metalworking activity that context should be sampled throughout (at its social and economic context. produced the debris. Careful recording of the 0.2–0.5m intervals) in order to examine the residues can indicate the direction from distribution of . A 0.2 litre sample Structures and context which the material was dumped, and so is adequate for magnetic susceptibility The most useful contexts are those within suggest where the metalworking activity was screening and quantification of hammerscale, buildings or areas where metalworking was located. Large features often contain larger, as at Burton Dassett (Figure 5 and Mills and practised (primary deposits). More and therefore more representative, deposits of McDonnell 1992). Samples should also be frequently, however, metalworking debris metalworking debris. The proportion of taken from contexts spatially and is recovered from middens, pits and ditches, features left unexcavated should be recorded chronologically removed from the iron- or from where it was used for surfacing to provide a means to estimate the total working areas, for comparison. paths (secondary deposits). The excavation quantity of slag. of the two types of deposit needs to be All charcoal associated with metalworking approached in slightly different ways, since Finds and sampling features and debris should be collected for the type of evidence recovered and its Finds include ores, slags, fragments of hearth species identification and tree age – this can interpretation is different. or furnace structure, crucibles, moulds, metal provide important evidence on the stock, scrap and waste, and iron or stone management and exploitation of wood In primary deposits, metalworking structures metalworking tools (hammers, tongs, etc). resources for metalworking. Radiocarbon (furnaces, hearths and pits) might be Three-dimensional recording of bulk finds, samples should be processed in the usual encountered, and the distribution of the such as slags, is not usually feasible or manner to avoid contamination. residues within a building can be crucial in desirable, but crucibles, scrap metal, etc should identifying and separating different activities. be treated as ‘registered finds’. Where large The identification of metalworking finds and For example, on an iron-smelting site, quantities of debris are recovered, it can be debris usually requires that they are cleaned. charcoal production, ore roasting and bloom difficult to make a distinction between Some materials, however, are delicate and may smithing might also have been carried out. structures and finds; for example, a large be damaged; any cleaning procedures must be The excavation of areas where metalworking dump of slag can be considered as a structure agreed with the metalworking specialist and/or was done requires gridding and careful or as a large quantity of finds. Sampling conservator. Materials that should not be sampling, both for hand recovered material strategies should be tailored to the size and washed (except by, or under the supervision and soil samples for micro-residues, in nature of the debris recovered. Best practice is of, the metalworking specialist) include particular hammerscale (see below). to initially retain all excavated bulk finds and crucibles, moulds, hearth and furnace linings. Some knowledge of the relevant metalworking soil samples. Where circumstances permit, a processes is greatly advantageous when site reference collection should be established Lead waste and some minerals are toxic. excavating furnaces and ground-level hearths. by the metalworking specialist. This will form Those handling or cleaning these materials The dimensions and layout (plans and the basis on which all slags and residues will should complete risk assessments and/or sections) of these structures should be be classified. COSHH assessments. recorded. Sometimes it might be necessary to ‘unpeel’ them layer by layer to understand Slag, ores, crucible and furnace fragments are Bulk finds, such as slag, should be packaged how they were repaired or modified during usually large enough to be easily recognised; in tubs or heavy-grade plastic bags. In most use. The relationships between furnaces or some residues, however, are so small that they cases they are extremely robust and do not hearths and other features (buildings, pits, appear only as coloured ‘soil’ deposits. Some require specialised storage conditions. Slags etc) should also be carefully recorded. It is of the more important evidence, in the form of with a high metallic iron content (test by possible that waist-high or above-ground hammerscale from iron smithing, is too small magnet), however, should be treated as metal hearths existed but do not survive. It is to be noticed during trowelling but can be finds, ie stored under conditions of low sometimes possible, however, to reconstruct detected using a magnet. Soil samples should relative humidity. Debris recorded as their positions from an examination of the be taken from contexts containing ‘registered finds’ should be packaged distribution of metalworking debris. hammerscale, particularly primary contexts. individually and particular care should be taken with delicate materials, such as ceramic moulds. All debris must be kept, for examination by a metalworking specialist.

Dating The date of the archaeometallurgical activity on a particular site will affect its significance. It is not currently possible to date slag directly. Metallurgical processes, and the debris they produced, often remained virtually unchanged for very long periods. A range of other evidence can be used to determine date, however, including material culture, radiocarbon dating, dendrochronology and archaeomagnetic dating. Mining and smelting

Figure 5 Plot of magnetic susceptibility readings, with darker tones indicating higher values (corresponding to higher sites, however, often yield very little datable concentrations of hammerscale), within the medieval smithy at Burton Dasssett, Warwickshire.The building is 12m long. material culture. This might, in part, be due to

6 a focus on the obviously ‘technological’ aspects For large assemblages of metalworking debris, should be compared with other broadly of such sites (hearths, furnaces, slags heaps, the assessment may be carried out on a sub- contemporary sites locally, regionally etc); excavation of ancillary areas will increase sample of the available material. The sub- and nationally. the likelihood of recovering datable artefacts. sample should include examples of all the Most metalworking activities made use of different types of artefacts, and debris, This information will enable an assessment to charcoal fuel that can be radiocarbon dated. recovered, and should also reflect the full be made of the significance of the evidence Samples should be 100g of clean, short-lived range of contexts excavated. The selection of and of the requirements for the analysis charcoal, preferably relatively large fragments a sub-sample should be agreed with the phase. The assessment report should set out (Mook and Waterbolk 1985). Waterlogged metalworking specialist. On sites where little the procedures for further work and specify metalworking sites (especially mines and evidence of metallurgical activity is present, any scientific analysis required (chemical water-powered furnaces) can yield timbers the assessment is often the final opportunity analysis, micro-structural examination, etc). that can be dated using dendrochronology to examine the material. In these cases the The specialist will also be able to advise (English Heritage nd; 1996). The final use of total assemblage can be examined and where the evidence for metalworking does fired clay structures, such as hearths and interpreted in sufficient detail for inclusion not justify further work. furnaces, can be dated archaeomagnetically within the final excavation report. More (see p 24). complex and important assemblages are often Analysis and report preparation assessed in far less detail, with the assumption The analysis phase consists of the examination Site archive that an analysis phase will follow. of those records and materials identified during The product of the fieldwork phase of the the assessment phase, and the production of a project is the site archive, which should It is extremely important that the publication text that reflects the importance of include all the fieldwork data and a brief metalworking specialist is provided with a the results. The analysis phase can provide statement of the nature of the stratigraphic, brief summary of the site, including information on the range of metals worked, the artefactual and environmental record and stratigraphic and contextual data. Information technologies used, the social and economic finds. The Roman and Medieval Finds on related features and finds assessed by other importance of these activities, trade and Groups have issued guidelines (Cool et al specialists should be made available. Metal exchange, and cultural affinities. 1993) defining a minimum standard for the and fired clay objects – such as ingots, bar recording of all registered finds and groups stock, scrap, waste, unfinished artefacts, The metalworking specialist will provide of bulk finds. The site archive should include metalworking tools, crucibles and moulds – reports on features and/or groups of material plans, sections and context records relating to are particularly important. that have been identified as having potential metalworking features, finds and debris and for analysis and that are linked to specific the records relating to the contexts in which The metalworking specialist will make an objectives in the updated project design. All they were found. The presumption within assessment of the archaeological value of the metalworking debris must be made available English Heritage and Historic Scotland is metalworking evidence, which is dependent to the specialist for study during the analysis that projects will normally proceed to on a number of factors. The most important phase of a project. The entire assemblage assessment and usually to the analysis phase, is the current state of knowledge of that should be visually examined, classified and so there is no need to produce detailed metalworking process. For example, evidence identified as far as is possible (see below). catalogues at this stage. for medieval or earlier copper smelting in The finds should be weighed and/or counted England is extremely limited, so any early and recorded by context. Dimensions should Assessment of potential for analysis smelting is important. At some periods, some be recorded where appropriate – for example An assessment report consists of a summary processes are relatively well known (eg diameters and depths of furnace or hearth of the data and a statement of the academic medieval iron smithing), and such sites would bottoms, size of crucibles, diameter of hole in potential for the site and recommendations be particularly important only where primary tuyère mouths or blowing holes. The for further work, storage and curation. This deposits survive in good condition. The evidence should be compared with the phase is an opportunity to update the specialist will note any important or unique stratigraphic record in order to examine research design in the light of the discoveries features of the excavation record and spatial and chronological patterns in made, and to decide which parts of the data recovered finds and debris. The site metalworking activities (see Figures 6 and 7). warrant further investigation (analysis phase). It is important that all the evidence for metalworking is considered as a whole (features and slags, as well as metallic and ceramic materials). Where possible all material remains should be seen by a single specialist. Alternatively, several specialists might be involved, but provision should be made to integrate their work.

The metalworking specialist will classify the debris into different types depending on relatively simple characteristics (colour, density, size, shape, surface morphology, etc). Many of the recognisable types of debris are diagnostic of particular processes. In addition, the total Figure 6 Plan of the excavated features at the Roman site of Shepton Mallet, Somerset, where iron smelting (yellow) and quantity of debris should be determined. smithing (red) were taking place. Note the partial spatial separation of the two activities.

7 surface analysis can be performed without damage to the artefact. Scientific analysis of slags, crucibles and other debris can identify the metals being worked or the specific process being carried out (temperature, reducing conditions, etc). Finished metal objects, miscast objects, waste and other debris can be chemically analysed to determine their composition. With metal objects, the composition of the bulk metal or of an inlay or plating can be an aid to accurate description. A group of related artefacts could be analysed to show patterns of alloy use. Distinctive trace element ‘fingerprints’ can suggest a provenance for the artefact or for the metal of which it is made.

The benefits of chemical analysis of metal artefacts can be illustrated through recent work on Roman copper alloys. Analysis has been used to revise typological classifications of artefacts such as brooches Figure 7 The histogram shows the proportions of different types of slag for each phase of occupation at medieval (Bayley 1998), and has shed light on the Wigmore Castle, Hereford and Worcester. ways in which copper alloys reflect wider processes in society such as Romanisation Quantification 61kg of charcoal and produced 6.1kg of slag. (Dungworth 1997). Achieving a reliable estimate of the total The ratios of raw materials, waste and quantity of debris present in any partly finished product are likely to vary The microscopic examination of polished excavated, or unexcavated large feature (such considerably depending on the type and sections of metals (metallography) and as a slag heap) is difficult, but may indicate quality of ore, the technology used and the metalworking debris can reveal information the scale of activity on the site. The volume skills of the metalworkers. A certain amount about how objects were formed. of the features should be estimated and the of information on these variables can be Metallography has been applied to copper proportion of slag determined. The gained from chemical and mineralogical alloy, and especially to iron, artefacts to proportion of slag within a context might analyses of representative samples of ore, slag show the wide variety of techniques used by vary considerably between different features and charcoal. Such analyses can be integrated early metalworkers (eg McDonnell and and sites and can best be determined by with an examination of the wider landscape Ottaway 1992; Tylecote and Gilmour 1986; excavating a section. The total volume of slag and its use (eg Mighall et al 1990). Wilthew 1987). (in cubic metres) should be multiplied by the density of the slag (3–4.5 for most slags) to Scientific techniques Dissemination give the total weight in tonnes. In order to determine the full range of The results of analytical work should be technologies employed, a metalworking integrated into the excavation report. The The quantity of metalworking evidence specialist might need to use physical and format and approximate length of reports recovered can be used to provide data on chemical analytical methods to determine a should be agreed before work is started. resource exploitation, such as charcoal range of properties, such as chemical or Archaeometallurgical data and interpretations production and woodland management. The mineralogical composition, melting point, can be integrated into the main excavation evaluation of resource implications depends density, etc (see p 23). This should only be report, be published separately (with a on the accurate quantification of diagnostic carried out, however, where there is a summary in the excavation report) or both. debris, a full understanding of the specific archaeological question that has The exact format depends on the nature of metallurgical process and the precise nature been identified in the updated project the archaeology, the ways in which it was of debris (ore, slag, charcoal, etc). Bloomery design that is likely to be answered by investigated and the importance of the iron working is currently the only process scientific techniques. archaeometallurgical results. In some that is sufficiently well understood for such projects, dissemination may also be analyses to be possible. The ratios of ore, The method of analysis chosen depends through temporary or permanent displays charcoal, slag and bloom have been explored mainly on the questions asked. Some types of in a museum. through experimental reconstructions of iron chemical analysis are quantitative, providing smelting and smithing (eg Cleere 1976; Crew precise information about composition in Strategies for the storage of metalworking 1991). In one experiment (XP27, smelting a percentages or parts per million; others give debris need to be flexible and take into phosphorous-rich bog ore in a low, non-slag qualitative results, identifying the main account the size and significance of the tapping shaft furnace, Crew 1991), 7.6kg of elements or compounds present, and provide assemblage. A full copy of all data produced bog ore was smelted and yielded a 1.7kg a rough idea of relative concentrations. Some must be supplied for inclusion in the site bloom of iron. This was then smithed into a methods require small samples that will be research archive (Museums and Galleries 0.45kg bar and the whole process required destroyed by the analysis, but in other cases Commission 1992; Owen 1995).

8 Archaeometallurgical Iron in summary processes and finds – iron Plain iron contains less than 0.1% of other elements and is often known as ferritic iron. It has ° and its alloys a melting temperature of 1545 C. Alloys include (~ 0.3 to just over 1% ), phosphoric iron (up to 1% phosphorous), low carbon iron (up to 0.3% carbon), and Background (~ 2 to 5% carbon). Iron (Fe) is the fourth most abundant Process Description Archaeological debris element in the earth’s crust. suitable for smelting occurs in many locations, so Bloomery An inhomogeneous solid bloom of Fuel, ore, vitrified furnace lining and archaeological evidence for smelting is smelting metal was produced, as the metal did slag. Usually large amounts of slag geographically widespread. The methods of (7th C BC – not melt during the process.The will be recovered, including tap slag 16th C AD main product of these furnaces was or large slag blocks.The bases of producing iron and its alloys, and the extent and later in plain iron but other alloys were furnaces and tapping pits sometimes to which the alloys were used, changed with some areas) commonly produced as well.The survive. Hammerscale is often found, time. The terminology used within impurities present in the ore reacted as the iron bloom was usually archaeometallurgy to describe these processes with some of the iron oxide to form consolidated on the smelting site. and materials has varied, so the terms used in iron-rich slags. There is sometimes later evidence these guidelines are defined below. for waterpower. Blast furnace These furnaces operated at higher Ore, fuel and bloomery furnace slag, Plain iron is very pure: it contains less than smelting (15th C temperatures and produced liquid the last of which was sometimes 0.1% of other elements. It is often described AD onwards) cast iron, which was cast into objects smelted in blast furnaces. Large as ferritic iron because structurally it is made or ingots. Limestone was added with quantities of blast furnace slag were up of many crystals of a type known as the ore and reacted with the produced.The furnace rarely survives ferrite. Its melting temperature is extremely impurities present to produce a to any height. Remains of associated calcium-rich (rather than an iron- buildings, possibly with casting pits or high, about 1545ºC, so rather than being rich) slag and this increased the iron mould fragments. Evidence of melted it was forged into shape. Alloys of yield of the furnace. Cast iron could waterpower should be expected. iron melt at lower temperatures than plain be refined to produce a bloom of iron and have different properties. Early iron plain iron (or lower carbon alloys) is typically heterogeneous and a mixture of in finery or forges.The alloys can be present in one object. bloom was then consolidated in a chafery forge.

Alloys of iron and carbon are given different Smithing Most iron alloys were shaped, by Smithing hearth bottoms, names, depending on the amount of carbon smithing or , while solid.The hammerscale and vitrified hearth they contain, because this has a great effect metal was heated and then shaped lining. Ground level hearths might on the structure and properties of the alloys or welded. survive. Evidence of waterpower and thus on their potential applications. Low might be found. carbon iron is an alloy containing up to 0.3% Steel Steel was produced: during smelting Evidence of early steel production carbon. Steel contains from 0.3 to just over production in bloomery furnaces, by is in the form of objects, bars, 1% carbon. Steel is an ideal material for carburisation of plain iron, by billets or blooms containing steel. cutting edges on tools and weapons because cementation steel making and by The cementation process and when it is cooled rapidly, or quenched, it reducing the carbon content of cast Huntsman’s method produced becomes very hard, and if it is then heated, or iron. Huntsman’s method of making diagnostic evidence: fired clay from tempered, it becomes tough as well. Cast iron homogeneous steel was developed in cementation chests, and heavily the 18th century. vitrified crucibles and frothy slag contains 2–5% carbon, which lowers the from Huntsman’s method. melting temperature of the alloy to below 1200ºC. This alloy could be melted, and therefore cast to shape, but it was brittle. In this country the bloomery process was which was cast to shape. Cast iron was brittle, Carbon alloys can be produced during used for iron smelting until the 16th century however, and not suitable for all applications. smelting, owing to the presence of the AD – and later in some areas – when it was Refining processes had to be used to convert carbon-rich fuel, or afterwards, by heating the superseded by the blast furnace process. The it into tougher, forgeable iron alloys when this iron in the presence of a carbon-rich temperatures achieved during the bloomery was required. For this reason blast furnace material, such as charcoal. process do not far exceed 1250ºC, which is smelting, and the subsequent refining, is well below the melting point of the plain iron sometimes referred to as an Indirect Method Phosphoric iron contains up to 1% (and low carbon and phosphorus alloys) of forgeable iron production. phosphorus, which makes it harder. The generally produced. Therefore the metal does phosphorus enters the metal from the ore not melt during the process. The bloomery Bog ore was probably a major source of iron during smelting. Its presence also influences process is sometimes referred to as the Direct ore, especially for the bloomery process. It is the uptake and distribution of carbon and Method of forgeable iron production because formed by the precipitation of iron this might be the reason that phosphoric iron it produced, in a single process, types of alloy compounds, in lakes, bogs and other poorly and ores were selected or avoided for that could be forged by a smith. drained locations, and could simply be dug specific applications. out. Other recognised sources of high quality In contrast, blast furnaces, introduced to iron ore include limonite (hydrated iron Smelting Britain c1500AD, produced cast iron. The oxide), siderite (iron carbonate) and The bloomery and blast furnace processes lower melting temperature of this alloy meant haematite (iron oxide), and these were are the two main methods of smelting iron. that the furnace produced molten metal, extracted by mining. Raw, or untreated,

9 ores rarely occur in any quantity on from clay, although some stone and tile were archaeological sites. If ores with higher iron occasionally used. The clay was often contents were smelted, the yield of iron could modified with large amounts of temper, such be improved and less waste produced. as small stones, pieces of slag and possibly Therefore, where possible, iron-rich ores were organic material. Sand was sometimes added selected, perhaps washed, and then roasted in to the clay for repairing the high-temperature a roasting hearth before being smelted. These zones of the furnace, to make it more processes reduced the quantity of impurities, temperature resistant. Clay bricks of a collectively known as gangue, which entered distinctive shape have been found on some the furnace and thus reduced the amount of Roman smelting sites. The basic furnace was waste produced during smelting. Other usually a cylindrical clay shaft, probably geological formations contain less iron and are 1–1.5m high, with an internal diameter of not suitable for bloomery smelting; they can 0.3–1m. The walls of the furnace were be confused with iron slags (p 22). Roasting normally at least 0.2m thick, to reduce heat Figure 10 Vitrified clay lining with a blowing hole, from the changes the colour of the ore, making roasted loss from the furnace. To achieve sufficiently Roman site at Ribchester, Lancashire. Note the slag attached below the blowing hole. Vitrified furnace lining is ore easier to spot on archaeological sites. The high temperatures for smelting, air was produced by a high temperature reaction between the ore was also crushed to increase its surface forced into the furnace near its base through clay lining of the furnace and the alkaline fuel ashes or slag. The outer parts are usually orange (oxidised-fired) area and hence the rate of reaction, although one, or sometimes more, small holes around ceramic, while the inner zone is grey or black (reduced- if ore is crushed too finely the particles can the circumference. These air inlets are often fired) and often vesicular with a glassy surface. Furnace clog the furnace. Small particles, known as referred to as tuyères. There is a growing linings might have been repaired repeatedly or replaced, and can show a sequence of vitrified layers. Although ore fines, are found in areas where the ore tendency, however, to describe the actual furnace walls were relatively thick, usually only the inner was roasted, crushed or stored, and holes in the furnace wall as blowing holes, to surface survives, or is noticed, as the heat of the furnace will not have fired the outer part. The hottest area of the sometimes in and around furnace structures. differentiate them from any separate pipe or furnace was near the blowing hole (see photograph), and nozzle, historically called tuyères, used for consequently vitrified clay lining containing the preserved channelling air into the blowing hole. In the outline of the hole is often recovered. From the Roman and medieval periods there is some evidence for the use majority of furnaces, an arch through the wall of replaceable circular or rectangular blocks of clay, with a at the base enabled slag to be removed – blowing hole, that could be set in place in a prepared cavity in the furnace wall. These are often referred to as either cold, or as hot tapped slag, often into replaceable block tuyères. an adjacent pit. While not in use the arch would be temporarily blocked. In the hottest zone of the furnace, near the blowing holes, the temperature exceeded 1250°C. Here the liquefied slag separated from the solid iron metal particles that had Figure 8 Roasted and crushed iron ore, prepared for formed and flowed to the bottom of the smelting experiments. (Photograph by Peter Crew). furnace. The iron particles coalesced and Iron ores vary in colour and can be difficult to spot, particularly if they have not been roasted, as they do not eventually formed a spongy lump known as a necessarily have a strong colour or high density. Roasted ores bloom. The bloom usually attached to the (see photograph) are commonly red, purple or orange, because they are oxidised. Ore fines are small particles of furnace wall just below the blowing hole and roasted ore that sometimes respond to a magnet and have grew until it started to interfere with the air high magnetic susceptibility. Pieces of reduced ore, sometimes blast, at which stage it was removed, probably partially slagged, are sometimes found among the debris from the bottom of the furnace, and these are commonly through the top of the furnace. Since the iron grey. The minerals present in iron ores can be determined did not melt during the process, the bloom using X-ray diffraction, and the iron content can be determined by chemical analysis (p 25).The ores recovered Figure 9 Bloomery furnace reconstruction (external contained a lot of trapped slag and was during archaeological fieldwork need not be representative diameter 0.7m).The tapping arch, through which the liquid usually compositionally heterogeneous. slag enters the tapping pit, can be seen at the front of the of the ores smelted because, for example, they might have Therefore, although the main product of been discarded because they were of poor quality. furnace. See Figures 1 and 4. (Photograph by Sarah Paynter) bloomery furnaces was plain iron, the blooms The bloomery process The charcoal in the furnace was lit and the commonly included regions of other alloys as Charcoal was exclusively used as the fuel for furnace preheated. When hot, a charge of well, such as steel and phosphoric iron. bloomery smelting. Coal could not be used as roasted ore and charcoal was added to the it contains sulphur, which would be absorbed top, while bellows were used to pump air into by the iron, causing it to fall apart during the base of the furnace. The furnace forging. There are no known charcoal functioned as a result of two types of production sites prior to the medieval period, reaction: the reduction of the iron ore to iron but at early sites charcoal might have been metal and the reaction of impurities in the made in small pits adjacent to furnaces, as ore to produce slag. The iron ore was observed in other parts of Europe. reduced by carbon monoxide, produced by the reaction of oxygen with the charcoal. Furnaces rarely survive to any height, so their Reduction started high up in the furnace and likely structure and mode of operation have progressed as the ore particles moved down. been reconstructed by supplementing the The impurities, or gangue, in the ore are Figure 11 Iron blooms are rare finds on archaeological sites: archaeological evidence with ethnographic predominantly made up of silica and here an ethnographic example is shown. Blooms are made up of many small particles of iron coalesced into a spongy data and experimental work (eg Cleere 1971, alumina. These reacted with some of the iron lump.They are often badly corroded and fragmentary and Crew 1991). Furnaces were constructed oxide present to form a slag. are strongly magnetic.

10 Figure 15 Undiagnostic slags (from Housesteads, Northumberland) are small or fractured pieces of slag that have the dark colour of iron-rich slags, but do not have any diagnostic surface morphology. Therefore, although indicative of iron-working, they cannot be used to distinguish between smithing and smelting.They are sometimes the largest proportion of slags in an assemblage.

Figure 12 A consolidated iron billet from the Roman site at Westhawk Farm, Kent, that has been cut in half (max dimension 40mm). Partially consolidated billets are more common finds than blooms.They vary in size, are often badly corroded and fragmentary, and are strongly magnetic.

Different types of slag are produced during Large pieces of slag were often disposed of in bloomery-smelting and smithing processes. antiquity and might also have been moved These can be differentiated by their colour, during more recent agricultural practices, density, morphology and size, but often to field boundaries. Fuel ash slag compositionally they are all very similar. (see p 21) is also sometimes found on They are often described as fayalitic because smelting sites. they have compositions similar to that of the mineral fayalite (2FeO.SiO2), an iron silicate. There is no known evidence of either the tools or bellows used in the smelting process, If a very iron-rich ore was used in the except in some later literary sources. Some smelt, little waste slag was produced; it iron-working sites have produced evidence could remain at the bottom of the furnace Figure 13 Section through an Anglo-Saxon furnace bottom for fire-lighting, either as lumps of iron- without hindering the smelt, sometimes from Mucking, Essex. Furnace bottoms are dense, dark- pyrites, used to produce sparks, or fire-drill coloured slags that solidified in the furnace and can retain forming a furnace bottom. If the ore was the shape of the furnace base, sometimes with part of the stones with cup-shaped hollows, which would less rich in iron, then more slag was baked clay structure attached. Furnace bottoms are typically have been used as bearings for a fire drill. 0.3m in diameter and 0.2m high, and will often contain produced. This would eventually obstruct pieces of reduced ore and fuel. Shelter would have been essential for the the lower part of the furnace, so it had to be storage of ore and charcoal and for removed for smelting to continue. protecting the furnaces. Examples of round Removing the slag during the smelt, rather stake-wall smelting huts have been found on than allowing it to accumulate, enabled the prehistoric sites and large, square post-built smelt to continue for longer and a larger shelters are known on medieval sites. bloom of iron to be produced. The slag could be removed through a hole at the During the Middle Ages the hand-blown base, either by tapping when it was hot and bloomery was partly replaced by fluid (tap slag) or by raking while it was hot with water-powered bellows (and/or hammers and pasty (raked slag). In slag-pit furnaces, for primary smithing, described on p 15). known in Britain from the Anglo-Saxon Documentary sources suggest that there were period, the slag ran into a pit underneath developments in smelting technology and the the furnace structure itself, to form a slag Figure 14 Tap slag has a characteristic shape, resembling a bloomery furnaces themselves (Tylecote block. These are blocks of dense, dark flow of lava, with rivulets of slag on the upper surface and a 1986, 188–9). These later sites are at present rough under surface which may have adhering sand or clay. coloured slag, somewhat larger than furnace Tap slag is dense with few relatively large bubbles, as it poorly understood and therefore any medieval bottoms. The furnace superstructure could flows out while hot and fluid. It is dark in colour, usually grey site with evidence of water-powered iron then be relocated over a freshly dug pit. to black, sometimes with a liverish or maroon upper smelting is of importance (Cranstone 1991). surface.The size of tap slags can vary from individual runs Each of these methods of removing slag of a few hundred grams to accumulations weighing 10kg or gives it a characteristic morphology, and more. Hot, fluid slag can also form long, thin runs. The blast furnace therefore slags are classified largely on Documentary evidence suggests that blast this basis. Only the more common terms Much of the slag on a site might not be furnaces were introduced to this country are used here, but more complex slag diagnostic of any particular iron-working around 1500AD. Initially they used large classification systems have been developed process, being fragmentary, corroded or quantities of charcoal fuel, necessitating and used, particularly for unusual sites possessing intermediate characteristics, and careful woodland management to ensure and assemblages. is simply referred to as undiagnostic slag. adequate supply. Water was used to power the

11 bellows for the furnaces, so they are located in and made of leather and wood with iron river valleys, near the dam of a storage pond. nozzles, known as tuyères, which fitted The water-powered bellows gave a powerful through custom-made holes in the stone air blast allowing higher temperatures to be furnace lining. The casting house covered the reached. These temperatures were high area where castings were made, either using enough to react the gangue impurities present moulding sand for casting and small with lime (calcium oxide), producing a lime objects, or in a pit containing moulds for alumina silicate slag. This made the blast large objects such as guns. Fragments of furnaces more efficient at extracting iron moulds and casting pits can be found at sites. because the lime replaced iron oxide in the There would also be a large building nearby slag, and therefore almost all of the iron for storing the fragile charcoal, and another compounds in the ore could be converted to Figure 16 Blast-furnace slags are usually glassy in for storing ore (Bowden 2000). iron metal. Blast furnaces could even smelt appearance and range in colour from blue and green to grey or brown.They usually have abundant fracture surfaces bloomery-furnace slags, since these contained with little or none of the original surface remaining.They It was not until the early 18th century that fairly large amounts of iron that could be are less dense than bloomery-furnace fayalite slags, as they blast furnaces were fuelled by coke, which is contain much less iron.They do contain a small percentage extracted by the new, more efficient process. of iron however, which gives them their colour.These slags derived from coal, instead of charcoal. This It is not clear whether lime was introduced for can be found in large quantities and were often reused, for technology was slow to be adopted, but by this purpose in early blast furnaces or whether example as hardcore or scattered across fields to improve c1750 the technology was widespread and soil quality. it entered the furnace as an impurity, perhaps evolved rapidly. Coke ovens were developed, in the ore. By the 17th century, however, it refractory material, such as sandstone. This older furnaces were modified and the design was being introduced intentionally in the form material eroded gradually with use, but this of new furnaces changed. As coke is stronger of limestone. had the advantage of increasing the capacity than charcoal, the height of the furnace of the hearth, and thus the size of the castings stacks could be increased without danger of The blast furnace would work continuously for that could be made. There are some instances the stack contents compressing and inhibiting months at a time, in production runs known as of two hearths in one stack, in order to the air blast. Wedge bellows were replaced by campaigns, and was repaired between increase the capacity for large cast objects cast iron blowing cylinders, and then by campaigns. The charge put into the mouth at (Crossley 1990). There are also descriptions steam engines; firebricks were developed for the top of the furnace at regular intervals of small hearth extensions, called forehearths, furnace linings. The sulphur content of the would typically consist of iron ore, fuel and from which cast iron was ladled into small products and waste products (slags) of these limestone. The iron ore was reduced as it moulds, but as yet archaeological evidence of processes can be used to identify instances travelled down the furnace, and slag was also this has only been found for a coke-fuelled when coke was used as the fuel. formed. The conditions in blast furnaces were furnace (described below). more reducing than in bloomery furnaces, Refining cast iron causing more carbon to enter the metal. The There were other structures associated with When forgeable iron alloys were required, product of blast furnaces was cast iron, which the furnace. The bellows were housed in the conversion or fining processes were used to has a lower melting temperature than plain blowing house, built alongside a water wheel convert the cast iron produced by the blast iron and was therefore molten. It was tapped for power. Earlier bellows were wedge-shaped furnaces into a product similar to that of the off at intervals and could be cast straight into objects such as guns, or into ingots. These castings were linked to a supplying channel of metal, resembling a sow feeding piglets, and so the castings were called pigs.

Blast furnaces were essentially tower-like constructions: the tower is known as the stack and the hearth is at its base. Early blast furnaces were stone-built, strengthened with external timber frames, and were usually square in plan, although other shapes are known. Typically they were 5–6.5m square and, although no early stacks survive, a documentary source estimates a height of 6m.

Later furnaces became taller, but were also built more solidly. It was normal practice to build two arches in the stack, in adjacent sides. One arch was for the air blast from the bellows and the other was for casting the iron and tapping the slag. Within the stack, the lining of the hearth (where the molten slag and iron collected) and the lower part of the stack were replaced at the end of each Figure 17 Reconstruction of Duddon blast furnace, Cumbria, which was built in 1736 and is now a Scheduled Ancient campaign. The hearth itself was made of a Monument. (Illustration by kind permission of Alison Whitby and the Lake District National Park Authority)

12 Archeo guidelines v10 hi res 28/6/02 11:45 am Page 13

bloomery furnaces, by reducing its carbon Making steel The initial stages of refining the bloom content. This took place in finery forges, Steel was produced by various methods at involved hammering it while hot to consolidate which were, in some cases, adapted different periods. The blooms from bloomery the metal and expel the trapped slag; losses at bloomery furnaces. furnaces were heterogeneous in carbon this stage can be considerable (Crew 1991; composition and there is evidence from the Craddock and Wayman 2000). This primary In this conversion process, cast iron from the Iron Age that steely portions of blooms were smithing was often carried out at the smelting blast furnace was remelted in an open selected for certain types of tool (Fell 1993). site, and therefore smelting and refining charcoal hearth under an air blast provided Whether steel was also produced in dedicated residues can be found together. The iron stock, by water-powered bellows. The carbon in the bloomery furnaces, by manipulation of the or billet, produced would then undergo iron was oxidised and removed and a bloom smelting conditions and types and ratios of secondary smithing or forging, also while hot, of low-carbon iron would form in the hearth. raw materials, is unknown. The varied to produce artefacts. Secondary smithing also Slag was also formed, but this was liquid at properties of iron alloys were certainly includes the repair and recycling of iron objects. these temperatures and so was largely recognised and exploited during the early separated from the bloom. The hot bloom medieval period (Gilmour and Salter 1998). The properties of iron and its different alloys was taken to a water-powered tilt-hammer for have been described (p 9) and the smiths’ skill forging, which removed most of the trapped Another method of making steel was to encompassed the control and appropriate slag and shaped the metal into a bar. The surface carburise or case harden iron objects application of these properties in forming repeated heating that was required in this by heating them in a bed of charcoal. Carbon objects. Smiths recognised that not all iron process could take place in the finery hearth from the charcoal entered the outer surface of behaved in the same way, and stock metal with or in a separate hearth, sometimes known as the iron, creating a shell of steel. If the object different properties would have been available. the chafery, which was also blown by water- was then quenched the shell became hard. For example, Iron Age currency bars are powered bellows. There is growing evidence that this method thought to be a form of stock iron and the was known in the Iron Age (Fell and Salter elaborate socketed ends or welded tips on Coal or coke could not be used in the early 1998) and it was widely employed in the these bars are a significant feature, bloomery and blast furnaces or finery forges medieval period. demonstrating visibly the forging properties of because of its high sulphur content, which the iron. Finds – such as blooms, billets and had a detrimental effect on the forging Documentary evidence suggests that the bars and all forms and types of stock iron – properties of the metal. It could be used to cementation method of making steel was are important to further research into the fuel the chafery hearth, however, since the introduced in the 17th century. Plain iron bars trade and use of different iron alloy types. fuel in this process was simply required to were packed in charcoal in a clay chest that reheat the iron. Archaeological evidence for was sealed and heated to increase the carbon Objects were formed from a combination of finery and chafery forges can include the content of the iron. The bars were then different iron alloys. For example, knives wooden foundations for the forge hammers broken, reforged to improve their were made with a hard alloy for the cutting and the wooden support for the , plus homogeneity, and reformed into steel bars edge and a tough alloy for the back; pattern- evidence to indicate the presence of water (Cranstone 1997; Barraclough 1984). The welded weapons were made from different power to drive the bellows for each hearth interior brickwork of surviving cementation alloys welded together and repeatedly folded and the hammer. The hearths themselves furnaces is vitrified and pieces of fired clay, and twisted during forging to obtain an were above floor-level and therefore rarely used to seal the chests and later broken off, attractive patterned surface (Gilmour and survive. Fining generated various types of can also be diagnostic. In the 16th century Salter 1998). Some iron is lost during debris, including hammerscale, a small some steel was made by partly decarburising smithing, and this loss is greater during quantity of flowed slag that resembles tap cast iron, using a similar process to fining, but complex smithing operations such as slag, large slag lumps and a type of porous stopping before all of the carbon was removed . slag, sometimes with traces of flow on the (see Refining cast iron, above). surface. Finery or chafery forge debris can be distinguished from that found on smelting At the end of the 1740s, the development of sites by the absence of ore. very refractory clays made Huntsman’s crucible method of steel making possible, Once coke was being used to fuel blast although the process was not much used furnaces, sulphur from the coke entered the before the last decades of the 18th century furnace products. Many conversion forges (Craddock and Wayman 2000). This method had trouble producing forgeable iron from involved breaking up cementation bars, coke-smelted pig iron because of the placing them in crucibles, and heating them in impurities, and the finery process had to be a furnace to melt and mix the alloy, before adapted accordingly. A period of variability casting more homogenous steel ingots. The and innovation followed, as attempts were crucibles used in this process became heavily made to perfect a larger-scale, more efficient vitrified and the slag that was produced had a process. Eventually the reverberatory frothy appearance. puddling furnace, for converting cast iron, was developed in the 1780s. Puddling Smithing furnaces produced slag very similar in Bloomery smelting of iron results in a composition to that from bloomery furnaces, heterogeneous bloom, containing quantities of Figure 18 Late medieval illustration showing smiths at work. but with a higher sulphur content, indicative trapped slag, which must be refined to produce Note the waist-level hearth in the background and the anvil of the fuel used. iron stock suitable for forging into objects. set in a wooden block.

13 Smithing takesplace in a hearth or forge. Iron could also be smithedusing ground- hammerscale) consists of smaIl droplets of A shelterwould protect the hearth,and the levelhearths. solidified slag produced during primary smith, from the elementsand also causedim smithing as slag was expelled from the lighting round the hearth,allowing the smith Early primary smithing hearthswere bloom, so spheroidal hammerslag can be to betterjudge the temperatureof the iron sometimescircular -easily confusedwith found among smelting debris. It is also from its colour.The smith would heatthe the basalremains of a furnace.The hearth produced during secondary smithing by metalto red heatin the hearth for shaping. was filled with a bed of fuel, predominantly welding processes. Using hand tools and working on an anvil, charcoal,but from the Romanperiod the metal could be thinned down, thickened, onwardsthere is growing evidencefor the Hammerscale not only indicates that smithing sttaightened,bent, split, pierced and use of coal (Dearne and Branigan 1995). An took place on a site, but can also locate the otherwiseshaped. Iron could alsobe welded air blast was used to obtain high activity precisely because it is often found in by heating the piecesto be joined to white temperatures.A smithing hearth consistsof the immediate vicinity of the smithing hearth heatand then hammering them together;this a clay hearth wall, or some other device for and anvil (see p 24). The anvil residues can is known as fusion or fire welding.When iron separatingthe bellows from the hot fuel, become trampled into a smithing floor, which is hot, however,an oxide scalerapidly forms with a blowing hole-'throughwhich air was becomes cemented together with iron on the surface,which can sometimesinhibit blown into the fuel bed. (Blowing holes are corrosion products into smithing pan. the formation of a good weld.The scalecan sometimescalled tuyeres:for clarification see be removedby using a , suchas sand, p 10).Vitrified clay hearth wall or hearth Slagforms as the iron heatsin the hearthfrom which reactswith the iron oxide scaleand lining is most likely to be produced in the reactionsbetween the fuel,the hearthwall and forms slag.At welding temperaturesthe slag hottest part of the hearth,around the oxidisediron. Droplets of slagaccumulate in is fluid and is squeezedout from the join blowing hole.Vitrified clay nea;;l:h-liningsare the hot regionnear the blowing hole, when the piecesof metal arehammered similar to furnace linings (p 10), though coalescingto form a largespongy lump, together.Fluxes appearto be unnecessaryin hearth lining is generallythinner and is knownas a smithing hearthbottom, whichis many circumstances,however; for example, found in smallerfragments and smaller discardedby the smithbefore it beginsto plain iron canbe welded without using a flux. quantities.Sometimes the outline of the hinderthe efficientoperation of the hearth. The extentto which fluxes were used in blowing hole is preserved.Fuel ashslag was Thesebulky smithingslags may be found antiquity is unknown. sometimesalso produced (p 21). heapednear to the smithy or may be transportedfarther awayfor dumping or Medieval and later forges were waist high, Srnithingproduced hammerscale. Flake reuse,for examplein road construction. and there is documentaryand artistic harnrnerscalewas produced in both primary evidencefor this type of hearth dating back and secondarysrnithing when a hot iron Evidence of the structure that housed the to the Roman period; archaeological object,with an oxidised surface,was struck. smithing hearth sometimes remains. Stone evidencefor suchhearths rarely survives. Spheroidalhammerslag (also knownas and hammer stones with stagged

Figure 19 Scanning electron mi(:ros(:ope (SEM) image of flake hammers.:ale and spheroidal hammerslag. Flake hammersc:ale Figure 20 Smithing pan from the Roman site at Westhawk (:onsists of grey to bla<:k,fistrs<:ale like fragments. typic:aJly 1-3mm a<:ross.1tssmall size means that it is ra",ly detected during Fanm,Kent tt consists of a layer of debris, largely ex(:avation but it is sometimes ",(:ove",d from environmental Samples or from soil samples taken spedfi(:ally to ",(:over hammerscale, trodden down and corroded together (image hammers(:ale. Flake hammersc:ale is highly magneti(: and (:an be separated from soil using a magnet Spheroidal hammerslag 1000m high) l (often also ",fe~d to as hammerscale) (:onsists of Srl)ail round slagdroplets. whic:h can be hollow to varying deg",es. It is usually magneti(:. Figure 21 Cross section of a smithing hearth bottom.These surfaces have also been found. There might are normally plano-convex to concavo-convex in section also be indications of the location of a and circular or oval in plan.Their size and weight can vary considerably, from 100g to more than 2kg, although the wooden anvil or a wood block into which a majority weigh 200–500g.The upper surface sometimes has small metal anvil was inserted. Metal tools a depression produced by the air blast, or is sometimes irregular, where the last formed slags have not been fully such as anvils, tongs and hammers do incorporated. The lower surface usually has impressions survive, but hardly ever in a workshop from charcoal or the hearth lining.The size of the cake context. There is no evidence for the type of depends on the amount of iron forged, how much slag it contained, whether fluxes were used and how often the bellows used at early sites, although their hearth was cleaned out.The larger smithing hearth cakes location can sometimes be inferred. From at can easily be misinterpreted as furnace bottoms. Smithing hearth bottoms from primary smithing, or refining will least the 12th century, waterpower was generally be larger than those from secondary smithing. harnessed to drive the hammers to Smithing hearth bottoms are sometimes slightly magnetic as they can contain fragments of iron broken from the bloom consolidate blooms (Astill 1993). Waterpower and some hammerscale. was also used to power the bellows and evidence of associated devices – such as grindstones – is also sometimes preserved.

Archaeometallurgical Copper in summary processes and finds – copper Copper is a soft and ductile metal, with a melting temperature of 1084°C. Alloys of copper and its alloys include brass (with zinc), bronze (with tin) and gunmetal (with tin and brass). Sometimes lead was also added and the alloys are then described as leaded. Background Process Description Archaeological debris Pure copper has a melting point of 1084°C, lower than that of plain iron, and is a very Smelting Ores were smelted in one or more There is little evidence for early versatile metal. Copper and copper alloys can stages. Molten metal was produced. copper smelting, although it is likely be melted and cast to shape or can be Later, complex smelting operations that debris such as slag and vitrified clay would have been produced. In wrought. Copper is very ductile and soft, and and then reverberatory furnaces were introduced. later periods there can be evidence so can be drawn into long wires or hammered for waterpower. into thin sheets. Although similar terms are usually employed for describing the alloys of Casting Metal could be melted in a crucible Crucibles, moulds, metal spills, failed copper, they are not always used to mean the and cast directly into objects or into castings and surplus metal trimmed same thing. Therefore a definition of terms is ingots using moulds. Moulds were from castings (sprues, flashings and made from sand, clay, metal or stone runners). always helpful when alloys are being identified and could be open or closed, one and described. The common alloys of copper piece (investment mould) or two discussed in these guidelines are bronze (piece mould). (copper with tin), brass (copper with zinc) and gunmetal (copper with tin and zinc). If Wrought metal The solid metal was shaped, for Scrap metal, such as turnings or working offcuts, metal sheet, rods, bars and lead is also added, then the alloy is described example by cutting or hammering, which, if done at room temperature, wires. Small ingots or blanks, tools as leaded, for example ‘leaded bronze’ and so caused the metal to harden and and anvils are rarer finds. on. Alloying increases the hardness of the become brittle. Heating () Waterpower can be used for metal, reduces the melting temperature, and the work-hardened metal at intervals mechanised processes at later can increase the strength and also change the restored its toughness and softness. periods. colour. Bronze and brass were used for wrought and cast objects, but the uses to (chalcocite Cu2S and chalcopyrite CuFeS2). techniques to the Lake District and to south which each alloy was put tends to vary with While the smelting methods used in antiquity Wales in particular. The smelting operations time. Additions of lead to copper alloys could are not known, replication experiments have consisted of a complex sequence of steps, improve the quality of castings, but was shown that copper carbonate and copper producing, first, matte and eventually copper detrimental for alloys that were to be worked oxide can be smelted directly, using charcoal metal. At the end of the 17th century, or gilded. fuel and an air blast to obtain sufficiently high reverberatory furnaces were introduced and temperatures. The molten metal sometimes the elaborate Bristol and Welsh smelting Smelting and alloying forms prills (droplets) scattered through the processes were developed. Small, simple, Very little physical evidence for pre-Industrial smelting slag, which forms from the reaction water-powered copper smeltmills also appear Revolution copper smelting in Britain has of gangue in the ore with metal oxides, or to have been used in some areas (Day and been recovered, even though it is likely that sometimes coalesces into a pool of metal. Tylecote 1991). identifiable debris, such as vitrified clay lining Evidence from other parts of Europe suggests and slag, would have been produced. that the commoner sulphide ores were The alloy bronze could be produced by Fourteenth-century documentary records smelted to produce a cake of matte (copper smelting tin and copper ores together, but refer to the working of copper ores in Devon sulphide), which was then resmelted to give most bronze was probably produced by (Claughton 1992). Typical copper ores, which copper metal. remelting together metals that had been are found only in parts of the Highland Zone, smelted separately. Brass was not made until are copper carbonate (malachite In the 16th century the Company of Mines the Roman period; its production is

Cu2CO3(OH)2) and copper sulphide Royal introduced German workers and described in the section on zinc (p 21).

15 Figure 22 Drawings of common crucible forms of Iron Age to post-medieval date. 1: Iron Age, 2 and 3: Roman, 4 and 5: Anglo-Saxon, 6: early Christian, 7: later medieval, 8: post-medieval. The grey tone represents added clay, either lids (2 and 6) or extra outer layers (3 and 7).

Casting the side or lid. These lids and knobs are Refined and alloyed molten metal could be mainly Early Christian/Middle Saxon in date. cast directly into objects or into small ingots. Open, one-piece ingot moulds were made Moulds might be open or enclosed and were from stone or fired clay. Melting small made from a variety of materials: sand, clay, amounts of copper does not necessarily metal or stone. Moulds for small objects require a custom-built hearth. Consequently were usually made of either fired clay or, less crucibles, the vessels in which the metal was commonly, fine-grained stone. Clay moulds melted, moulds, used for casting the metal to are not common finds, partly because they shape, and the artefacts themselves are the are fragile and so do not survive well. The most common archaeological evidence for clay used to make moulds was carefully copper casting. To produce a casting, the selected and processed and was usually copper alloy would first be melted in a tempered with fine sand or organic matter. crucible, in a reducing atmosphere to prevent Clay moulds are invariably grey or black the metal from oxidising. The molten metal (reduced-fired) on their inner surfaces, was then poured into a mould through a which were in contact with the cast metal, funnel-shaped opening, the in-gate or sprue and orange-red (oxidised-fired) on the outer cup. It ran down through channels (runners) surfaces. Clay moulds were usually broken Figure 23 Roman crucible from Dorchester, Dorset into the actual shape to be cast (the matrix). open to recover the casting, so identification (120mm high). Crucibles are invariably grey or black as a of the objects cast is often difficult. When result of being reduced-fired. Crucible clay was usually tempered with fine sand or, occasionally, organic matter. Crucibles come in various shapes and sizes, clay moulds survive well, the way they were Crucibles can become vitrified because of the high from thimble-sized to larger than pint beer- made and used can be determined. Often temperatures at which they are used, either developing a thin external ‘glaze’ or becoming glassy and bubbly mug sized (Bayley 1988; 1990). From the the largest and most easily identifiable throughout their entire thickness. Some crucibles have an Roman period onwards some crucibles are fragments of ceramic moulds are the funnel- added outer layer of less refractory clay, to improve heat wheel-thrown, but handmade crucibles shaped in-gates. insulation and to increase the robustness of the vessel, and this usually becomes heavily vitrified. Small quantities of the continued to be used into medieval times. metal being melted can become chemically bound in the The larger sizes occasionally date to the Two main types of clay moulds are found, crucible surface, or physically trapped as droplets of metal. Copper can be seen as green corroding droplets or as Roman period but most are later medieval investment (lost-wax) moulds and piece bright red patches where it has reacted with the glassy or post-medieval (Bayley 1996). Some forms moulds. Investment moulds were made by first surface of the crucible. Chemical analysis (see p 25), are relatively well dated but simple handmade modelling an object in wax and coating it however, is often the only way of determining the process in which the crucible was used. thumb pots are virtually undatable. Most thickly in clay. The clay/wax assembly was then crucibles were open-topped, although a few fired and the wax melted or burnt out to leave types had lids or rims that were pinched a fired clay mould. Molten metal was poured together to produce an enclosed form. into the mould and allowed to solidify, then the A few crucibles had knob-like handles on mould was broken to remove the casting.

16 This increased hardness is often desirable, but it also leads to increased brittleness. If a large amount of working is required to produce a particular object, the metal must be heated between successive bouts of working otherwise it will eventually break. This heating stage is known as annealing, and it causes the structure of metal to recrystallise, restoring its original toughness Figure 26 Part of the cope from a cauldron mould from and softness so that working can continue. Prudhoe Castle, Northumberland, Note the inner surface Annealing takes place at temperatures that in reduced-fired (black) but the outer surface is oxidised- fired (red). could be achieved in a domestic hearth: less than 800 ° C.

Large ingots of metal are not usually found on wrought metal working sites. The metal workers used small ingots or blanks as their starting point, producing sheets, bars, rods and wires of metal, which were then worked further to produce finished objects using Figure 24 Part of an investment mould from Beckford, hammers, files, gravers, chisels, dies and Worcestershire. It has no mating surfaces since it was made punches. Anvils made of various materials, in one piece. Note the in gate at the top and the runner down to the circular object. such as bone, wood and iron, are occasionally found. The most commonly Piece moulds were formed in two or more found evidence of wrought metalworking sections. An original object, or a pattern made consists of small pieces of scrap metal, such in the desired shape, was pressed into a lump as turnings and sheet and wire offcuts. Metal of clay and locating marks made round the filings and offcuts were collected for edge. Another piece of clay was pressed over recycling, sometimes in boxes set into the pattern. The two valves of the mould were Figure 27 Sprue with two runners from Wicklewood, workshop floors (Figure 2 and Zienkiewicz then separated, the pattern was recovered, and Norfolk, cut from a copper alloy casting. 1993, figs 13–14). Whetstones and abrasives the mould reassembled and sealed (luted) with were used to create a good surface on metal more clay. The mould was then fired and used. Sometimes a tallow model was used, the mould objects, which were then polished. Although the valves of clay piece moulds could was formed around it, and then the tallow was Alternatively the surface could be burnished be taken apart, they were fragile and therefore melted out. Another method was to shape the with a hard material such as steel or agate are not likely to have been used more than inner part of the mould (the core) first, then to (Bayley 1991b). Visual or metallographic once. Stone and metal piece moulds were far make the outer part of the mould (the cope) examination of artefacts can provide more durable and would have been used many around it. The cope was then removed, in evidence for wrought metalworking times over (Bayley 1990; 1992a; 1992b). pieces if necessary, and the core trimmed (see p 24). Patterns in wood or lead for making piece down. When the mould was reassembled there moulds are also known, but rare. was a void left between the cope and the core mining to receive the molten metal. These moulds ORES

were broken to remove the casting. smelting

METALS

As well as the moulds themselves, corroded refining and alloying dribbles and spillages of metal may be found. ALLOYS

Castings were cleaned up (fettled), with melting and casting melting and casting surplus metal such as flashings (the metal CASTINGS INGOTS AND BLANKS that ran between the valves of a piece- smithing

mould), runners and sprues trimmed off, and fettling and casting PART-MANUFACTURES recycling these are also sometimes found. Failed finishing and decorating CAST OBJECTS WROUGHT OBJECTS castings, where the molten metal failed to use use completely fill the mould, are also found. BROKEN OBJECTS Figure 25 Complete clay piece mould for a trumpet brooch from Prestatyn, Clwyd.The in gate is by the foot of the Wrought metalworking brooch.The locating marks round the edges of the two halves (valves) of the mould, which would have aided correct Wrought metalworking describes the assembly, can clearly be seen. Fragments of luting clay, which processes of shaping solid metal, for example Figure 28 Flow chart showing how the product of one was used to seal the join, is also sometimes found. by hammering or cutting. Unlike ferrous metalworking process is the raw material of the next. Large objects such as cauldrons and bells were alloys, copper alloys can be easily worked at also cast in moulds. The process of making room temperature. The properties of the In the medieval period waterpower was these moulds is well known from medieval metal, however, are affected when it is cold- adopted for wire drawing, and for producing documents such as Theophilus’ De diversis worked. As the alloy is hammered, bent or sheet metal, driving battery hammers and, in artibus (Hawthorn and Smith 1979). twisted into shape, it becomes work-hardened. the post medieval period, for rolling mills.

17 Archaeometallurgical Lead in summary processes and finds – lead Lead is a very soft, dense metal with a low melting point of 327°C. Lead ores were often mined and smelted for the silver that they contained (p 19). Lead metal has a low melting point of 327ºC and lead ores can be reduced to lead Process Description Archaeological debris metal below 800ºC. Lead is very soft and Smelting Lead ores can be smelted at less Shallow clay depressions have been easily formed into sheets. It has a tendency than 800° C, so simple structures found from the Roman period. Later to creep, that is, to distort slowly over long could be used, which rarely survive. structures were sometimes stone periods of time. Because of its high density, Early furnaces (bole hills) made use built. Sparse vegetation can indicate lead was often used to make weights. of natural draughts. Later, bellows- lead contamination. Some slag and blown furnaces (ore hearths) were evidence of waterpower can be Alloys of lead and tin were used as soft developed, which were subsequently found.The flues of reverberatory solder and, from the Roman period adapted for waterpower. furnaces often survive. Reverberatory furnaces (cupolas) onwards, they are also used for casting developed in the 17th century and objects – which are described as pewter. were coal fired. Smelting produced molten lead metal and liquid slags. Smelting The lead-rich slags from early The common lead ore is galena (lead processes were often re-smelted sulphide, PbS) which often contains minor later. amounts of silver. The silver content was Lead working Owing to the low melting Ingots are quite common. Lead sheet, often the main economic reason for mining temperature of lead, domestic pots offcuts and lead-melting dross are and smelting the lead (see section on silver could be used instead of crucibles sometimes found. Moulds, failed and gold (p 19)). There is relatively little when melting lead. Limestone, wood castings and sprues indicate that lead archaeological evidence for early lead or antler moulds could be used was cast. smelting, even in areas near the ore sources instead of clay ones for casting lead. where it might be expected (the Mendips, Welsh borders and Pennines). was collected in a mould at the side of the kiln-dried wood, and the kilns can be found Lead ores were crushed to the optimum size hearth. This process was not efficient at near the ore hearth remains, but in the for particular smelting processes. In the extracting the metal, however, and much northern Pennines peat was used. Ores medieval period stamp mills were used for lead was lost into the slag. By the 1530s rejected by bole smelters, as well as bole this purpose but later, edge-runner mills boles had grown from c1–2m to 5m across slags, could be smelted in ore hearths. About became common. (Kiernan 1989). Bole sites are difficult to the same time shaft furnaces, known as locate. Often the best indicators are strips Burchard’s furnaces, blown by water- Early smelting structures were probably of ground with poor, lead-tolerant powered bellows, were also introduced. The insubstantial, and any slag produced has vegetation downwind of the ridges where ore hearths remained dominant, however, been scattered or was resmelted by later, boles were situated. changing only to incorporate water-powered more efficient, smelting processes. The bellows technology. remains of Roman period smelting structures are shallow clay bowl-shaped By the 17th century smelters were resmelting depressions, 1–2m in diameter. the slag from ore hearths in structures called slag hearths. These were usually water- It is generally assumed that structures, powered and fuelled by coke. Water-powered known as bole hills or boles, were being ore hearths continued to be used until the used to smelt lead by the Saxon period, and late 19th century (Tylecote 1986). these were the main medieval and Tudor method of lead smelting. Derbyshire boles Figure 29 Lead smelting slags are known in small amounts In the later 17th century the cupola was were simple structures consisting of a hearth from the Roman period onwards.They are usually glassy, introduced. These reverberatory coal-fired very dense and black, green or grey in colour. Such slag in a three-sided stall or stone-built enclosure often has a flowed surface, similar to iron-smelting tap slag furnaces consisted of a chamber containing in which pieces of rich ore and brushwood (image is 100mm across). the ore and another containing the coal fire. were stacked and set alight. In other areas The heat from the fire was drawn into the different structures were used, though the Bole slags were being resmelted using smelting chamber. The advantages of this process was the same. Areas with consistent charcoal fuel in a foot-operated, bellows- process were yet greater smelting efficiency winds were selected for boles because they blown hearth known as a blackwork oven in and fuel economy. From the mid-18th did not use a forced draft. Experimental Devon by the late 13th century (Claughton century this technology was rapidly adopted reconstruction has shown that it is not 1992) and in other areas somewhat later. and towards the end of the century the flues necessary to roast the ore before smelting, became very long and complex, with as this reaction occurs in the more oxygen- In the 16th century, lead smelters changed condensing chambers to collect residues. As rich zones at the top of the fire. The gangue from boles to structures known as ore the stone from these constructions has often in the ore reacts with some of the lead oxide hearths. Air was blown into the hearth with been robbed, frequently all that remains are to form a liquid slag – all that is often found bellows and this forced draft made the the trenches leading from furnace to to indicate the presence of a bole site. As process more efficient at extracting lead. In chimney. Such furnaces were used into the smelting took place, molten lead formed and Derbyshire these hearths were fuelled with 20th century (Crossley 1990).

18 Lead working not have to stand high temperatures. Roman Newly smelted lead was cast into ingots, pewter plates were cast in stacking stone often known as pigs, which are quite piece-moulds (eg Blagg and Read 1977). common, particularly from the Roman Antler burrs were carved to act as moulds period. The main evidence for lead working, for late Saxon brooches (eg Newman 1993). however, is lead melting dross. This is the As with copper alloy casting, sprues and oxidised layer of metal, which forms on the failed castings are sometimes found. surface of the melt and is skimmed off before the metal is poured. Other evidence of melting is harder to detect because any domestic pot could be used, instead of a crucible, owing to the metal’s low melting point. The low melting point also means that the metal can easily be accidentally melted, so the presence of melted lead is not necessarily an indication of lead working. Much lead was used as sheets and sheet offcuts are common finds. Lead from buildings was frequently recycled, being easily melted down and re-cast.

For casting lead or pewter objects, fine Figure 30 Lead melting dross that solidified in a hollow in Figure 31 A later medieval piece-mould made of fine- limestone, wood or antler moulds could be the ground, from Kings Langley, Hertfordshire. It is a mixture grained stone with holes for locating pegs at the corners of lead metal and oxides that were skimmed off the molten from Hereford (length 57mm). used instead of clay because the moulds did metal before it was cast.

Archaeometallurgical Silver and gold in summary processes and finds – Native gold is the principal source of gold. Silver is mainly obtained from lead ores (p 18). Silver other metals and gold are soft metals with similar melting temperatures to those of copper alloys.They were commonly alloyed with each other, and with copper and other metals.

Silver and gold Process Description Archaeological debris Unlike most other metals, the main source of Refining silver To separate silver from base metals Early cupels are ceramic (heating gold is native gold, rather than an ore. Silver and gold the cupellation process was used. trays). Later ones were made from was mainly obtained from argentiferous, or This involved melting the silver alloy bone ash. Litharge cakes are formed silver-rich, lead. Precious metals have similar with added lead and oxidising the during large-scale cupellation. melting points to those of copper alloys and melt. Cupellation could also be used were melted in clay crucibles. The metals to test the purity of silver (assaying). could be cast to shape or, more commonly, Shallow dishes (cupels) were used worked as solid metals. Both silver and gold for small-scale cupellation and assaying, but large-scale cupellation are very soft. They were alloyed with each took place in hearths. Gold refining other and with other metals, commonly and assaying usually did not use lead. copper, and the alloys have the advantage of being harder than the pure metals (Bayley Parting silver To part silver from gold, the silver Ceramic parting vessels. 1988; 1991b). from gold was removed by reacting it with salt. Later, strong mineral acids were used. Refining Gold and silver were often refined before use, copper and tin, were also oxidised and glassy surface. By 1600 AD cupels made from or reuse, as they were often significantly dissolved in the litharge. The litharge was then absorbent bone ash were being used in England. debased. The purity of gold could be absorbed into the dish or hearth on which Small-scale cupellation was used to test determined by using a touchstone, which was the process was taking place, leaving the prill the purity of a sample of precious metal: a a black stone used to obtain a smear of metal, of refined precious metal on the surface. process known as assaying. Analysis of the colour of which was an indication of its Small-scale cupellation could be carried out some heating trays used for gold assaying purity. The only effective way of determining on small shallow dishes, or discs, known as has failed to detect lead, indicating that the the purity of silver was by fire assay, using the tests or cupels. cupellation process was not used. Instead, cupellation process. the gold was probably melted in strongly From Roman and Saxon times small ceramic oxidising conditions to burn out the base Cupellation involved melting the metal to be dishes, often called heating trays, were used as metal impurities, perhaps with a flux of refined with an excess of lead. Under a blast of cupels and makeshift varieties were sometimes some sort. Ceramics used for gold assaying air, the lead was oxidised, forming litharge made from potsherds. The reaction of the are usually made of harder, more refractory (lead oxide). Any base metals present, such as litharge with these ceramics produced a fabrics than those used for silver.

19 Figure 35 Parting vessels were not always purpose-made and a wide variety of vessels were used; all were lidded or would have been sealed with clay.They are the only metal- working vessels that are normally oxidised fired.They are readily identifiable as they usually have a pale pink-purple colour on the inside rather than the orange-brown normally associated with oxidised-fired ceramics. Sometimes areas of lemon-yellow colour, specular haematite crystals (as here on a fragment from Lincoln), or even flecks of gold are visible. Some parting vessels show no surface vitrification, while others have a thick, exterior glaze that can Figure 32 Bone ash cupels from the Tower of London.They are pale coloured and powdery.The absorbed lead in these be turquoise or deep green. objects makes them noticeably heavy for their size.

Large-scale refining of silver using Tin cupellation took place in hearths lined with Tin is a soft, white metal with a melting point absorbent material, usually burnt and of 232ºC. Documentary and archaeological crushed bones (bone ash) or calcareous clay. evidence suggests that tin extracted from the

The litharge and any base metals soaked into ore cassiterite (SnO2) in Devon and Cornwall the lining but the precious metal was mainly was exported from the Bronze Age onwards left on the surface. The impregnated hearth and was of great economic importance. There linings that provide evidence for this process are two main sources of cassiterite in the are known as litharge cakes. region: stream tin and lode tin. The ore obtained from veins in the rock, lode tin, was When silver was extracted from argentiferous less readily accessible than stream tin, which lead the same technology was used, also was eroded from rock, largely separated from Figure 33 Ceramic cupel from York.The vitrified upper producing litharge cakes. These can be the gangue, and then deposited in streambeds. surface is rich in lead and highly coloured.There is a central distinguished from litharge cakes produced The stream tin was thus probably the first to depression where the assayed metal solidified. Sometimes droplets of silver or gold that failed to coalesce became by silver refining as there are normally no be exploited and it only required washing trapped in the area surrounding the depression. other metals present and the cake size is far before smelting. By medieval times the ore larger, up to 600mm across and 60mm thick. from lodes, which contained large amounts of This pure litharge is dull red in colour, but gangue, was mined and so grinding and the cakes usually have a cream-coloured, washing was necessary before smelting weathered surface. (Gerrard 1997; 2000). ‘Black tin’ is the term applied to both stream tin and to crushed and Parting cleaned lode tin. Cupellation could not be used to separate, or part, silver from gold, so a different Smelting technology was developed. The There is little archaeological evidence for archaeological evidence for parting has only early tin-smelting processes. A number of tin recently been recognised. Parting involved ingots have been found with a roughly plano- making the mixed metal into thin sheets, convex shape. The latest date to around the packing them into a pot interleaved with a 13th century, indicating that smelting ‘cement’ of crushed brick or tile mixed with technology probably changed little up to this salt, sealing up the pot and heating it, but to a time. The ingots are thought to have been temperature below the melting point of the formed by molten tin-metal cooling in small metal. The salt reacted with the silver in the bowl-shaped furnaces. In medieval smelting, metal, forming silver chloride, which was molten tin was tapped from the furnaces. volatile and was absorbed by the cement and Although both the metal and the iron-silicate the walls of the pot. When the pot cooled, the slag were liquid, the two would separate out gold could be removed and remelted and the because of their different densities. In the Figure 34 Segment of a litharge cake from Thetford, Norfolk. Examples up to 200mm in diameter and 30mm cement smelted to recover the silver (Bayley post-medieval period, lime was substituted for thick are known.They have a flat or convex base and 1991a). With the introduction of distillation iron oxide in the smelting process, blast normally have a central depression in their upper surface. They are very heavy for their size because of the lead in in the later medieval period, the method of furnaces were used to achieve higher them and are fairly powdery and friable. Litharge cakes vary parting changed to one using strong temperatures and calcium silicate slags were in colour from grey to greenish if much copper is present. mineral acids. produced (Tylecote 1986).

20 The crushing of lode ore took place in atmosphere (one containing little oxygen) in and the shape slumped and distorted. Some stamping mills. They used water-powered the crucible, so the zinc ore was reduced to bricks were deliberately vitrified to change hammers, probably from the 13th century. zinc metal vapour, which was absorbed by their appearance. Stamp mills can be positively identified by the solid copper granules. The absorption of the presence of mortar stones with saucer- zinc lowers the melting temperature of Silicate materials, such as clay and stone, will shaped hollows in which the ore was copper, so eventually the metal melted, form a glass at lower temperatures if fluxing crushed. The partly crushed material from homogenising the mixture (Bayley 1998). compounds are present. Common fluxes are the stamp mill was ground to a fine powder Reverberatory furnaces for roasting calamine the alkalis – soda and potash – found in in a crazing mill. Around the mid-16th were introduced by the late 17th century. plant ashes. The ash from a fuel will thus century most crazing mills were abandoned Zinc smelting, using sealed retorts in conical react with the silicates in clay or stone vessels because of the introduction of the more furnaces, was introduced in the 18th century or hearths to produce glassy (vitrified) efficient wet stamping process. Water was in the Bristol area and more efficient materials. These glassy wastes are usually used to separate the cassiterite from the processes were introduced in the 19th described as fuel ash slag. Similarly, the gangue and the dressed ore was smelted century. Archaeological evidence of these ashes from burnt thatch or structural timbers in a furnace within the blowing house. processes is rare. may flux daub walls, during a house fire, to Charcoal or carbonised peat was used as the form vitrified clay. An equivalent process fuel. Water-powered bellows provided an air Non-metallurgical high produces vitrified forts when their timber- blast to the furnace. The molten tin was laced ramparts are burnt. Fuel ash slag and tapped from the furnace hearth into a trough temperature processes vitrified clay can be produced in any high- and was then ladled into smaller moulds or temperature fire in which alkalis and silicates troughs. These troughs, often hewn from Many non-metallurgical processes generate come in to contact and so, on their own, they granite blocks, are good indicators of a materials that can be easily mistaken for are not indicative of a metallurgical process blowing house. See Gerrard (2000) for metallurgical waste. High temperatures can (Bayley 1985, Biek and Bayley 1979). further details. be produced in ovens, hearths, kilns (for ceramics or lime), furnaces (for making or Alkali fluxes and silica can also be reacted Tin was alloyed with copper to produce melting glass) and even when buildings burn together intentionally, to produce alkali silicate bronze, and with lead to produce pewter and down. These structures and many objects, glasses. The raw materials were first fritted, ie solders. High-tin pewter was used to make such as pottery vessels, are commonly made heated together in a furnace so that they objects in similar forms to contemporary from clay or stone, which contain silicates. If partly reacted. The frit produced was broken silver objects, because of its similar colour. It they are heated to sufficiently high up and placed in crucibles, together with was more rarely used simply as tin metal, as temperatures these materials can melt and recycled scrap glass cullet, and then heated in the softness of the metal made it impractical become glassy; they can then be confused the furnace more strongly to produce a for functional applications. It found favour with vitrified waste products from homogeneous melt. for decorative applications, however, as the metallurgical processes. Temperatures high white colour of the metal contrasted nicely enough to produce vitrification were rarely Glassy materials are also formed from the with copper coloured alloys. Other metals, achieved in antiquity, although occasionally reaction of lead oxide with silica-containing such as iron, were plated with tin. Tin, like pottery, brick and tile kilns became too hot materials, since lead oxide is also an effective lead, could also be melted in domestic pots and the ceramics inside were over-fired. flux. Lead silicate glasses are formed during instead of crucibles because of its low Pottery wasters are glassy and blistered, metallurgical processes involving lead but, melting point.

Zinc Any attempt to reduce zinc ore in the same manner as other metals using charcoal fuel at around 1000°C, would result in the zinc metal becoming a vapour as soon as it was produced (it boils at 907°C), which would be lost as fumes. Consequently zinc was not generally available in Europe until the post-medieval period; documentary evidence records zinc extraction from the 18th century.

From the 1st century BC, however, copper was alloyed with zinc by the cementation process; the resulting metal is known as brass. In this process zinc carbonate or zinc oxide, which were known as calamine in antiquity, were ground, added to granulated copper and charcoal in a closed crucible, and heated to between 950ºC and 1000ºC (below the temperature at which copper melts). The Figure 36 Fuel ash slags from Rivenhall, Essex.They are lightweight, vesicular and fragile, and are usually off-white to green or presence of the charcoal ensured a reducing mid-grey in colour, generally much paler than iron-working slags.

21 Figure 37 Ceramic crucible sherds with a thin layer of glass on the inner surface from Glastonbury, Somerset. Crucibles containing glass, dribbles of glass and lumps of glass cullet are all evidence for glass re-melting, which was commoner than glass making until the late medieval period. as with alkali silicates, can also form accidentally. For example, if a building is destroyed by fire then the lead in the roof flashings, plumbing, or window cames within the building will melt and oxidise. This lead oxide will react with silicate materials such as bricks or tiles to fuse them into a mass of vitrified debris. Figure 39 Daub and ceramic tiles from a Roman building in London destroyed by fire, which are stuck together by an As with alkali silicates, lead silicates were also accidentally-formed lead-rich glass. intentionally produced as glasses and enamels, Ceramic vessels were also used in the medieval and as ceramic glazes. Iron colours the glass period in the production of various chemicals. or glaze pale amber, brown or olive green, These processes were normally carried out at while copper produces bright green or opaque cooking temperatures and so did not produce red. Crucibles in which coloured glasses were vitrification, though powdery or crusty made have thick layers of glass on the inner deposits are sometimes left on the vessels. surface, unlike metal-melting crucibles where the glassy waste is mainly on the outside.

Some geological materials can be confused with iron-working slags in particular. Some forms of ironstone can be mistaken for tap slag or smithing slag. Pyrite (iron sulphide) nodules, pieces of puddingstone, bog iron ore and Niedermendig lava can all be confused with smithing slags. Deeply corroded iron objects and iron concretions are also apt to be wrongly identified.

Briquetage is the term given to ceramic containers in which seawater was evaporated to obtain salt. This resulted in a bleached appearance to the ceramic, which is usually fairly soft and oxidised-fired but does not Figure 42 An iron concretion consisting of pebbles and sand have any vitrified surfaces. grains bound together by iron compounds.They are Figure 40 Section through a puddingstone boulder; the amorphous orange-brown lumps that respond poorly to a rounded exterior can be mistaken for iron slag. magnet but do not have the typical vitrified surfaces of metal working debris.They form as a result of the re- deposition of iron compounds in a similar manner to the natural phenomenon of iron panning.The process is sometimes enhanced by the presence of iron objects or scrap metal.

Figure 38 Crucibles containing deliberately made opaque Figure 41 Pyrites nodule.The weathered outside (right) may red glass, from Chichester, Sussex. look like iron slag but the interior (left) has a silver colour and radial structure. 22 Definitions of commonly Mould Strength used terms One technique for shaping metals is to melt The strength of a material is a measure of the and pour them into a container. Once the stress (load per unit area) it can support Alloy metal solidifies it takes on the shape of the before failing. The properties of pure metals may be container. Moulds were usually made from dramatically changed by combining them or clay, but could also be made from metal, sand Toughness adding non-metallic elements to form alloys. or bone. Moulds were not usually exposed to Toughness is a measure of the energy For example, steel is an alloy of iron and high enough temperatures to vitrify them. required to break a material. It is difficult for carbon; bronze is an alloy of copper and tin. a crack to grow in a tough material, whereas Non-ferrous a crack in a brittle material, such as a glass or Crucible Non-ferrous metals do not contain iron. ceramic, will grow very rapidly. A crucible is a vessel to hold a metal while it The principal ones used before the Industrial is melted. Metals are melted to refine them or Revolution were copper, tin, lead, zinc, silver, Vitrification before casting them in moulds. Crucibles gold and mercury, and alloys of these metals. Vitrification is the change into a glassy were usually made from refractory ceramics (vitreous) state, brought about by heating a and, because they were exposed to high Ore material. The temperature at which this temperatures, the clay was sometimes Many rocks and minerals contain metallic change takes place can be reduced by the partially vitrified. elements but not all are ores. A rock presence of fluxes, which may be accidentally containing metallic elements can only be or deliberately added. Ferrous regarded as an ore if the technological, social Iron and its alloys are described as ferrous and economic conditions enable people to metals. The principal ones used before the extract the metallic element(s) by smelting. Scientific techniques applied were cast iron, steel, to metalworking phosphoric iron and plain iron. Refine The initial product of most smelting This section provides an introduction to a Furnace processes is an impure metal, which is then few of the scientific techniques that have A furnace is a structure used to hold the ore refined. The refining process depends on the been applied to the study of early as the metal is extracted from it by smelting. nature of the metal and the available metalworking, including geophysics, Furnaces were usually made from clay and, technology. Copper was often refined by microscopy and various methods of chemical because they were exposed to high melting and partially oxidising it to remove analysis. The data obtained can be used to temperatures, the clay was sometimes impurities. Iron, because of its high melting explore a wide range of issues, such as partially vitrified. The archaeological remains point, was often smithed to squeeze out slag resource exploitation, economy, trade and of furnaces and hearths are often similar. still trapped inside. exchange and cultural affinities.

Hardness Refractory The scientific study of early materials can Hardness is a measurement of the strength of Refractory materials are those which can provide a wealth of information about the a material (its ability to resist plastic stand high temperatures without vitrifying. raw materials and manufacturing techniques deformation). Hardness is measured by used. Only the most commonly used making an indentation in a polished sample Slag methods are described. of metal, usually with a diamond and a Slags are vitreous waste products of many known weight. metalworking activities. Slags can be X-radiography produced during smelting, refining, smithing X-radiography is an imaging technique that is Hearth and even during casting of metals. Most ores particularly useful for examining and A hearth is a structure used to obtain the contain unwanted components (eg silica) and recording archaeological metalwork and some temperatures necessary to work metal, the these are removed as a slag during smelting. types of debris. The main archaeological exact temperature depending on the metal The size, shape and composition of slags are applications are the identification of objects being worked and on the process used. related to the processes that produced them. and examination of their morphology, Hearths were used to melt non-ferrous alloys methods of construction and condition. in crucibles, anneal copper alloys and heat Smelt X-radiography has been used to identify iron before smithing. Hearths were usually The process of extracting metal from ores is inlays, stamps, weld lines and pattern-welding made from clay and, because they were smelting. This is usually carried out at high in iron artefacts, examine crucibles and exposed to high temperatures, the clay was temperatures in a furnace, using a fuel such moulds (where metallic particles might be sometimes partially vitrified. The as charcoal. trapped in the ceramic fabric), distinguish archaeological remains of hearths and slag from corroded iron artefacts, and detect furnaces are often similar. Smith hammerscale and other debris in soil samples. Most metals can be shaped while solid by Mine hammering (smithing). In some cases (eg Geophysics In order to obtain ores it is usually necessary iron) the metal needs to be heated in a hearth Geophysical techniques have considerable to dig into the earth. In many cases this to make it sufficiently soft to allow easy potential in the study of early metalworking might consist of little more than a pit or smithing. In some cases (eg copper alloys) a sites and are useful tools for assessing the scale, quarry. The term mine is usually reserved for metal is made much harder by smithing. This date, preservation and significance of sites the more complex system of tunnels, adits work- can be removed by heating (English Heritage 1995; Gaffney and Gater and shafts that are used to extract ore. (annealing) the metal. 1993; Gaffney et al 1991; Vernon et al 1999).

23 The two geophysical techniques most high values (Mills and McDonnell 1992). which it was treated during manufacture and commonly applied on metalworking sites are Survey of non-ferrous metalworking sites use. Metallography can also identify the magnetometry and magnetic susceptibility. should detect hearths and areas of burning, methods used to apply surface treatments, and possibly large dumps of crucibles, moulds such as gilding, silvering and tinning. The Magnetometry with a fluxgate gradiometer or or other debris. Domestic hearths, however, shape of the inclusions shows the way the a total field instrument (eg caesium vapour) is can give similar signals. artefact has been wrought. usually carried out as a prospection technique, as these instruments can take readings Archaeomagnetic dating Different iron alloys (plain iron, steel and continuously, making it possible to survey Archaeomagnetic dating is a technique that phosphoric iron) can be identified using a large areas quickly. Gradiometers record can be used to date the fired clay of furnaces, microscope. If a material has been heat treated localised variations in the gradient of the hearths and slag that have cooled in situ or quenched, for example to increase the earth’s magnetic field. These variations can be (Aitken 1990). Materials such as clay, which hardness of the metal, this will also be caused by fired structures and magnetic contain a significant proportion of magnetic apparent. Steel and iron were sometimes materials (metallic iron and some slags) as well minerals, acquire a remanent magnetisation welded together to form composite artefacts. as by underlying geology. High-resolution when they are fired. This magnetisation is in Such structures are frequently found in edged gradiometer surveys, in which the data is the same direction as that of the Earth’s tools and weapons. Techniques for combining gathered at smaller intervals than the norm magnetic field at the time. The precise different alloys may have important cultural (for example 0.25m), are used for direction of the Earth’s field varies over time; implications. For example, in many Saxon distinguishing features such as furnaces, hence, if a fired clay feature is found that has knife blades a steel cutting edge was butt typically 0.5m in diameter. not moved since it was last fired, it is possible welded to an iron back, while Anglo- to date the firing using the direction of Scandinavian smiths favoured ‘sandwiching’ Magnetic susceptibility is a measure of the magnetisation recorded in the feature. the steel between two low carbon sides. degree to which a body becomes magnetised. Samples for archaeomagnetic dating should Human activity can enhance the susceptibility be taken by, or under the supervision of, a of surrounding soils. Magnetic susceptibility is relevant specialist. rarely used for surveys of large areas, but detailed work can be very informative. This Microscopic examination 0 1a 1b 1c 1d 1e technique has the advantage of only measuring Optical and electron microscopes can provide to a depth of about 100mm below the coil invaluable information on the surface condition Iron (depending on the size of the coil), therefore and internal microstructure of a wide range of Piled reducing the amount of interference from materials, including metals and metalworking Steel nearby features with strong responses. It can debris. The principal types of microscope used 2a 2b 3 4 5 provide an estimate of, for example, the are low and high power optical microscopes, amount of hammerscale in a sample because and scanning electron microscopes. Figure 43 Schematic sections through knife blades showing this can be related to the signal magnitude. different methods of construction (after Tylecote and Gilmour 1986, fig 1). Measurements are made either on the soil in Low power (x1–20 magnification) optical situ or on samples recovered from a site examination can reveal traces of metal on (including cored samples). crucibles, traces of silvering or other decoration The shape of the metal crystals in non- on a metal artefact, or tools marks and other ferrous alloys will show how the object was In situ smelting furnaces result in distinctive features diagnostic of the method of produced, for example cast alloys generally dipolar features in magnetometer surveys, manufacture (eg casting seams). It should be have characteristic dendritic structures. An which can be further emphasised if the data is used before other analytical or investigative additional tool frequently used in not clipped and is plotted on a coloured scale. techniques in order to evaluate what further metallography is hardness testing, which Magnetic susceptibility surveys can also analysis will be useful, whether there are any gives a direct measurement of the mechanical indicate, by a high response, the location of features in particular that require analysis, for properties of small samples. iron working. Bloomery iron slag typically example decorative inlay, and also to ensure that produces a higher magnetic response than any data obtained is from representative areas. Scanning electron microscopes (SEM) use a topsoil. Magnetic surveys of slag-rich areas beam of electrons, rather than light, to usually produce a very ‘noisy background’, High power optical microscopes (x50–1000 examine a sample. The advantages of electron with extreme peaks. Large dumps of slag magnification) can only be used on flat, microscopes are that a much greater can be so strongly magnetic that they polished specimens to determine the internal magnification and depth of field can be distort the magnetic field for several metres microstructure of materials. Scott (1991) obtained. Images can be obtained in two around, masking responses from adjacent provides a good introduction to the structure modes. Secondary electron mode is used to occupation features. of metals, metallography and the phase look at the topography or shape of a sample diagrams that help explain the microstructures (see Figure 19). Back-scattered electron Survey of iron smithing sites can reveal strong it reveals. Metallography requires the removal mode shows the compositional differences magnetic responses in areas (workshops) of a small sample, which is then mounted in a across a sample, since areas with different where hammerscale is concentrated. A resin block and polished. compositions are seen as varying shades of ground-level hearth should also provide a grey (Figure 44). Sample preparation significant response, although waist-high Metallic samples can be etched to reveal the techniques vary depending on the mode in hearths rarely survive in situ. The position of crystal structure of the metal. From this an which the SEM is to be used. It can be used such a hearth (or of an anvil) can be indicated assessment can be made of the type of alloy, in conjunction with analytical techniques by a low response in an area surrounded by its mechanical properties and the ways in (EDS and WDS), which are described below.

24 detectors (WDXRF) measure the intensity of A number of analytical techniques exist in each characteristic peak individually. EDXRF which characteristic spectra are generated as is relatively cheap and quick and can light rather than X-rays. The techniques determine the presence of most elements commonly used in archaeology are atomic within a few seconds. WDXRF is more absorption spectrometry (AAS) and expensive and slower but is more accurate and inductively coupled plasma atomic emission can detect smaller amounts of each element. spectrometry (ICP-AES). For these EDXRF can be used qualitatively on whole techniques a small powdered sample, such as artefacts (so long as they can be fitted into a drilling, is taken. The sample itself is the sample chamber – typically 100mm destroyed during analysis as it is dissolved in Figure 44 A back-scattered electron image of iron working across) and causes no damage. Used in this acid. These techniques can give very good slag showing several different phases. way, EDXRF permits the identification of accuracy, with detection limits below 1ppm the range of elements present in a material, for some elements, but they are most Chemical analysis for example the technique can determine if appropriate for bulk analysis of A variety of different analytical techniques are a crucible was used for melting copper homogeneous materials rather than for available depending on the questions that are alloys or silver. Alternatively, EDXRF can analysis of particular features. being asked, the nature of the material, and be used quantitatively, but this is only constraints associated with sampling, costs and possible where samples (typically a few Mass spectrometry time. The most common analytical techniques millimetres across) are removed, mounted The most sensitive analyses of archaeological determine either the chemical or mineralogical in resin and polished. metalwork are those made by mass composition of a material. The determination spectrometry (eg ICP-MS), where atoms, of the chemical composition of a material can Similar spectra are also generated using an ions or molecules are sorted and counted by be qualitative (simple presence or absence) or analytical SEM fitted with an energy mass. The principal application in quantitative (proportions of different elements dispersive (EDS) analyser. Alternatively an archaeology is the analysis of lead isotopes in in percentages or parts per million). Many SEM can incorporate wavelength dispersive lead, copper alloys and silver. The relative archaeological materials are heterogeneous and spectrometry (WDS) and, if dedicated to abundance of these isotopes characterises the corroded; therefore, analysis of very small analysis using WDS, is referred to as a ore source, but the isotopes in different samples or of surface layers can be misleading. microprobe, and the technique as electron British ore sources are similar. X-ray fluorescence (XRF) is the most widely probe microanalysis (EPMA). used method of chemical analysis in X-Ray diffraction archaeology. A beam of X-rays is directed onto Most analytical SEMs permit great X-ray diffraction can determine the structure an object, or sample, which then emits an flexibility. Multiple element analysis can be of a compound, as opposed to the chemical X-ray spectrum. The spectrum contains peaks undertaken of a single spot (down to a few composition. A small powdered sample is for each of the elements present in the object microns in diameter) or of larger required. XRD is useful because many or sample. Peaks for organic materials cannot predetermined areas. Line scans and maps materials contain the same elements but have usually be detected with EDXRF. The spectra can be used to show the distribution of different structures, for example iron ores. are detected in one of two ways: energy- individual elements in one or two This technique can only identify crystalline dispersive detectors (EDXRF) allow the dimensions. This is particularly useful for materials. Glass is not crystalline, but XRD simultaneous detection of the whole X-ray the analysis of such heterogeneous materials analysis could detect crystalline glass spectrum, while wavelength-dispersive as slags and iron. colourants or opacifiers if these are present. This technique is also useful for analysing corrosion products, precipitated salts,

80 pigments and soil samples. Sn

60

Sn 40 cps

Pb Pb 20

Cu Zn

Figure 46 False-colour back-scattered electron image of a 0 litharge cake showing several different phases.The green 5 1015 keV 20 25 30 areas represent a lead-copper oxide phase; the blue unreacted bone ash hearth lining, the red a tin-calcium-lead Figure 45 An XRF spectrum obtained from a crucible used oxide phase; and the yellow droplets of silver metal (image Figure 47 XRD spectrum of the metal patina from the for melting copper alloys, from Mucking, Essex. width c1mm). Quadriga, Wellington Arch, London.

25 Where to get help

Advice is available to curators and Centre for Archaeology British Museum contractors, archaeologists, conservators and (incorporating the former Ancient Department of Scientific Research, London museum professionals. The number of active Monuments Laboratory) WC1B 3DG archaeometallurgists is small, but most of them would rather be consulted than find out English Heritage, Centre for Archaeology, Paul Craddock too late about missed opportunities. Fort Cumberland, Fort Cumberland Road, 0207 323 8797 Eastney, Portsmouth PO4 9LD [email protected] The English Heritage Centre for Archaeology and the Archaeology Committee of the Justine Bayley Several individuals work on Historical Metallurgy Society run occasional 023 9285 6794 archaeometallurgical projects but their activities training days for archaeologists on how to [email protected] are normally restricted to sites being excavated recognise and deal with slags and other Iron Age to medieval metal and glassworking; by the Museum or research on finds in the industrial debris. If you would like artefact analysis Museum’s collections. information on future Slag Days, please write to David Dungworth at the address below. David Dungworth Cardiff University 023 9285 6783 School of History and Archaeology, Cardiff Some archaeologists and finds researchers [email protected] University, PO Box 909, Cardiff CF10 3XU have developed skills in the excavation of Metalworking and artefact analysis metalworking sites and in the identification Kilian Anheuser and assessment of archaeometallurgical finds. Sarah Paynter 029 2087 5157 They are often the best source of advice in 023 9285 6782 [email protected] the early stages of a project. They normally [email protected] Analysis of ferrous and non-ferrous do not, however, have access to the scientific Metal and glass working; artefact analysis metalwork and fine art facilities that can be used to check identifications and undertake detailed Advice is available to all, free of charge. If prior Analytical services (including metallography) investigations. arrangements have been made, assessments and available at cost. analysis of finds from EH-funded projects will be The institutions listed below all have one or undertaken free of charge. It is sometimes Durham University more scientists on their staffs who are possible to provide a similar service for Department of Archaeology, South Road, capable of providing metallurgical advice and developer-funded excavations, although a charge Durham DH1 3LE services, including scientific analyses of is normally made for this work. Material that objects and samples. Some specialise in contributes to current research projects is dealt Chris Caple identifying metalworking debris, while others with free of charge, even when not from EH- 0191 374 3627 focus on the application of a particular funded projects. [email protected] scientific technique. Where appropriate, they will refer you to another specialist. The Phil Clogg individuals’ special interests are listed below, Bradford University 0191 374 3215 but most are able to provide advice on a Ancient Metallurgy Research Group, [email protected] wider range of topics as well. Department of Archaeological Sciences, Analysis of archaeological materials, Bradford BD7 1DP including geochemical survey (Please note that inclusion in this list is no commitment to provide help.) Gerry McDonnell Joint research projects, small and large, are 01274 233531 encouraged. Service work can also be undertaken [email protected] at cost. Ironworking, artefact analysis

Joint research projects, small and large, are encouraged. Service work can also be undertaken at cost.

26 Institute of Archaeology Nottingham University Scottish Analytical Services for Art University College London, 31–4 Gordon Department of Archaeology, University of and Archaeology Square, London WC1H 0PY Nottingham, University Park, Nottingham Unit J, 47 Purdon Street, Glasgow G11 6AF NG7 2RD Thilo Rehren Effie Photos-Jones 020 7679 4757 Julian Henderson 0141 337 2623 [email protected] 0115 951 4840 [email protected] Analysis of metal and glass working processes [email protected] Analysis of glass Advice and analysis can be given on artefacts Postgraduate teaching in scientific analysis of and industrial waste from archaeological and archaeological materials is undertaken. Local Matt Ponting historical/ex-industrial sites. Analytical services projects and post-excavation research are 0115 951 4815 are available at cost. encouraged. A wide range of appropriate [email protected] analytical techniques is available in-house and Analysis of metals (especially non-ferrous), University within UCL. glass and ceramics Department of Archaeology and Prehistory, West Street, Sheffield S1 4ET National Museums of Scotland This department will provide analytical services Chambers Street, Edinburgh EH1 1JF at cost. Barbara Ottaway 0114 222 2000 Paul Wilthew Oxford University [email protected] 0131 247 4143 Begbroke Science and Business Park, Sandy Casting, metallography and use-wear [email protected] Lane,Yarnton, Oxford OX5 1PF analysis; supervising postgraduate students Analysis of ferrous and non-ferrous metals and metal working debris Chris Salter Caroline Jackson 01865 283722 0114 222 2918 Kathy Eremin [email protected] [email protected] [email protected] Ironworking, artefact analysis Glassworking processes and products 0131 247 4201 Analysis of non-ferrous metals, metal Peter Northover Quanyu Wang working debris and glass 01865 283721 0114 222 2930 [email protected] [email protected] These specialists deal primarily, but not Non-ferrous metalworking, artefact analysis Experimental casting of copper alloys exclusively, with Scottish material. Brian Gilmour Evelyne Godfrey National Museums and Galleries 01865 552294 [email protected] of Wales [email protected] Production of phosphoric iron Department of Archaeology and Artefact analysis, especially ferrous Numismatics, Cathys Park, Cardiff metallography Jim Symonds CF10 3NP 0114 222 5106 Joint research projects, small and large, are [email protected] Mary Davies encouraged; advice and support are given to Director of ARCUS (Archaeological 029 2057 3228 student and society projects. Analytical services Research and Consultancy at the University [email protected] available at cost. of Sheffield) Artefact analysis Welcomes service work on sites and artefacts, Royal Armouries and consultancy on conservation at cost. This department deals primarily, but not Armouries Drive, Leeds LS10 1LT exclusively, with material from Wales. Welcome discussion of dissertation projects for David Starley MSc students, involving analysis of materials 0113 220 1919 from high temperature technologies. [email protected] Artefact analysis

The Royal Armouries deals mainly with arms, armour and material from military sites. No charges normally made for this sort of work.

27 Bibliography – 1996 ‘Innovation in later medieval urban – 1974 ‘The Roman iron industry of the metalworking’. Hist Metall 30, 67–71 Weald and its connexions with the Classis Aitken, M J, 1990 Science-based Dating in Britannica’. Archaeol J 81, 171–99 Archaeology. Harlow: Longman – 1998 ‘The production of brass in antiquity with particular reference to Roman – 1976 ‘Some operating parameters for Alcock, L, 1963 Dinas Powys. Cardiff: Britain’, in Craddock, P T (ed), 2000 Years Roman ’. Bull Inst Archaeol 13, University of Wales Press of Zinc and Brass. Rev edn. London: BM 233-46 Press, 7–26 Armitage, K H, Pearce, J E and Vince, Cool, H E M, Cowgill, J, Jennings, S, A G 1981 ‘A late medieval ‘bronze’ mould Bayley, J and Budd, P 1998 ‘The clay Jones, C E E, Summerfield, J, Swain, H from Copthall Avenue, London’. Antiq J moulds’, in Cool, H E M and Philo, C (eds) and Tribe, A 1993 Guidelines for the 61(2), 362–4 Roman Castleford. Excavations 1974–85. Preparation of Site Archives and Assessments of Volume I.The small finds. Wakefield: West All Finds Other Than Fired Clay Vessels. Roman Astill, G G 1993 A Medieval Industrial Yorkshire Archaeology Service, 195–222 Finds Group and Finds Research Group AD Complex and its Landscape: the Metalworking 700–1700 Watermills and Workshops of Bordesley Abbey. Bayley, J and Eckstein, K 1998 Res Rep 92. York: CBA Metalworking Debris from Pentrehyling Fort, Craddock, P 1990 ‘Copper smelting in Brompton, Shropshire. Ancient Monuments Bronze Age Britain: problems and Lab Rep 13/1998. London: EH possibilities’, in Crew, P and Crew, S (eds) Barraclough, K C 1984 Steel Before Early Mining in the British Isles, Maentwrog: Bessemer. 2 vols. London: Metals Soc Biek, L and Bayley, J 1979 ‘Glass and Snowdonia National Park Study Centre,69–71 other vitreous materials’. World Archaeol Bayley, J 1984 ‘Roman brass-making in 11, 1–25 – 1994 ‘Recent progress in the study of early Britain’. Hist Metall 18, 42–3 mining and metallurgy in the British Isles’. Blagg, T F C and Read, S 1977 ‘The Hist Metall 28, 69–83 – 1985 ‘What’s what in ancient technology: Roman pewter moulds from Silchester’. an introduction to high temperature Antiq J 57, 270–76 – 1995 Early Metal Mining and Production. processes’, in Phillips, P (ed) The Edinburgh: Edinburgh Univ Press Archaeologist and the Laboratory. London: Bowden, M (ed) 2000 Furness Iron: the CBA, 41–4 Physical Remains of the Iron Industry and Craddock, P T and Wayman, M L 2000 Related Woodland Industries of Furness and ‘The development of European ferrous – 1988 ‘Non-ferrous metalworking: Southern Lakeland. Swindon: EH metallurgy’ in Wayman, M L (ed) The continuity and change’, in Slater, E A and of Early Clocks and Tate, J O (eds) Science and Archaeology, Brooks, R R 1989 ‘Phytoarchaeology’. Watches: Studies in Post-medieval Steel (BM Glasgow, 1987. Oxford: BAR (BS 196), Endeavour 13, 129–34 Occ Pap 136). London: BM Press, 13–27 193–208 Buchanan, P T 1992 ‘Metalliferous plant Cranstone, D 1991 Metallurgical Sites in – 1990 Evidence for Metalworking. Datasheet communities: the flora of lead smelting in Britain: Priorities for Research and 12. Finds Research Group 700–1700 AD the upper Nent valley’, in Willies, L and Preservation. Hist Metall Soc Cranstone, D (eds) Boles and Smeltmills. – 1991a ‘Archaeological evidence for Matlock Bath: Historical Metallurgy Society, – 1994 ‘Early surface features of metal parting’, in Pernicka, E and Wagner, G A 58–61 mining: towards a typology’, in Ford, T D (eds) Archaeometry ’90. Heidelberg: and Willies, L (eds) Mining before Powder. Birkhäuser Verlag, 19–28 Buckley, D G and Hedges, J D 1987 The Matlock Bath: Hist Metall Soc, 144–7 Bronze Age and Saxon Settlements at – 1991b ‘Anglo-Saxon non-ferrous Springfield Lyons, Essex. Chelmsford: Essex – 1997 Derwentcote Steel Furnace. Lancaster: metalworking: a survey’. World Archaeol 23, County Council Lancaster Univ Dept Archaeol. 115–30 Burnham, B 1997 ‘Roman mining at Crew, P 1986 ‘Bryn y Castell hillfort – a – 1992a ‘Metalworking ceramics’. Medieval Dolaucothi: the implications of the 1991–3 late prehistoric iron working settlement in Ceram 16, 3–10 excavations near Carreg Pumsaint’. North-West Wales’, in Scott, B G and Britannia 28, 325–36 Cleere, H (eds) The Crafts of the . – 1992b Non-ferrous Metalworking from 16–22 Belfast: UISSP CPSA/Ulster Mus, 91–100 Coppergate. Archaeology of York 17/7. London: CBA Claughton, P 1992 ‘Medieval silver-lead – 1991 ‘The experimental production of smelting in Devon’, in Willies, L and prehistoric bar iron’. Hist Metall 25, 21–36 – 1992c ‘Viking Age metalworking – the Cranstone, D (eds) Boles and Smeltmills. British Isles and Scandinavia compared’, in Matlock Bath: Hist Metall Soc, 12–15 – 1998 ‘Excavations at Crawcwellt West, Technology and Innovation. Medieval Europe Merioneth 1990–1998: a late prehistoric 1992, pre-printed papers vol 3.York: Cleere, H 1971 ‘Ironmaking in a Roman upland iron-working settlement’. Medieval Europe 1992, 91–6 furnace’. Britannia 2, 203–18 Archaeology in Wales 38, 20–35

28 Crossley, D 1990 Post-Medieval Archaeology Foster, J 1995 ‘Metalworking in the British Hamilton, J R C 1956 Excavations in Britain. Leicester: Leicester Univ Press Iron Age: the evidence from Weelsby at Jarlshof, Shetland. Edinburgh: Avenue, Grimsby’, in Raftery, B with HMSO Cunliffe, B 1984 Danebury. An Iron Age Megaw, V and Rigby, V (eds) Sites and Sights hillfort in Hampshire.Volume 2.The of the Iron Age. Oxford: Oxbow, 49–60 Hanworth, R and Tomlin, D J 1977 Excavations 1969–1978: the Finds. London: Brooklands,Weybridge: the Excavation CBA Frere, S S 1983 Verulamium Excavations of an Iron Age and Medieval Site, vol 2. London: Soc Antiq 1964–5 and 1970–71. Guildford: Surrey Archaeol Soc Daniels R 1988 ‘The Anglo-Saxon monastery at Church Close, Hartlepool’. Gaffney, C and Gater, J 1993 ‘Practice Haslam, J 1980 ‘A Middle Saxon iron Cleveland Archaeol J 145, 158–210 and method in the application of geophysical smelting site at Ramsbury, Wiltshire’. techniques in archaeology’, in Hunter, J and Medieval Archaeol 24, 1–68 Day, J and Tylecote, R F 1991 The Ralston, I (eds) Archaeological Resource Industrial Revolution in Metals. London: Management in the UK. An Introduction. Hawthorn, J G and Smith, C S Institute of Metals Stroud: Alan Sutton/IFA, 205–14 1979 Theophilus. On divers Arts. New York: Dover Dearne, M J and Branigan, K 1995 ‘The Gaffney, C, Gater, J and Ovenden, S use of coal in Roman Britain’. Antiq J 75, 1991 The Use of Geophysical Techniques in Hinton, D A 2000 A smith in Lindsey: 71–105 Archaeological Evaluations. IFA Tech Pap the Anglo-Saxon grave at Tattershall Thorpe, Lincolnshire (Soc Medieval Department of the Environment 1990 Gaskell Brown, C and Harper, A E T Archaeol Monogr 16). Leeds: Soc Planning Policy Guidance: Archaeology and 1984 ‘Excavations on Cathedral Hill, Medieval Archaeol Planning. PPG16. London: DoE Armagh, 1968’. Ulster J Archaeol 47, 109–61 Historic Scotland 1996 Project Design, Department of the Environment (NI) Gerrard, S 1996 ‘The early south-western Implementation and Archiving. Edinburgh: 1999 Planning, Archaeology and the Built tin industry: an archaeological view’, Historic Scotland Heritage. Planning Policy Statement 6. in Newman, P (ed) Mining and Metallurgy Belfast: DoE(NI) in South-West Britain. Hist Metall Soc, 67–83 Jones, S. 1999. ‘Great Orme, Bronze Age Dungworth, D B 1997 ‘Roman copper Smelting Site, Llandudno’. Archaeology in alloys: analysis of artefacts from northern – 1997 Dartmoor. London: Batsford/EH Wales 39,79. Britain’. J Archaeol Sci 24, 901–10 – 2000 The Early British Tin Industry. Stroud: Tempus Kelly, R S 1976 ‘Metalworking in N Wales English Heritage 1991 Management during the Roman period’. Bull Board Celtic of Archaeological Projects. 2nd edn. Gilmour, B and Salter, C 1998 ‘Ironwork: Stud 27, 127–47 London: EH technological examination of the knives, spearheads, and sword/weaving batten’, in Kiernan, D 1989 The Derbyshire – 1995 Geophysical Survey in Archaeological Malim, T and Hines, J The Anglo-Saxon Lead Industry in the Sixteenth Century. Field Evaluation. London: EH cemetery at Edix Hill (Barrington A), Chesterfield: Derbyshire Record Society Cambridgeshire. London: CBA, 250–56 – 1996 Waterlogged Wood – Guidelines on the Recording, Sampling, Conservation, Greene, J P 1989 Norton Priory. Lewis, A 1990 ‘Underground exploration and Curation of Waterlogged Wood. Cambridge: Cambridge Univ Press of the Great Orme copper mines’, in Crew, London: EH P and Crew, S (eds) Early Mining in the Griffith, F and Weddell, P 1996 British Isles, Maentwrog: Snowdonia – nd Dendrochronology. Guidelines on ‘Ironworking in the Blackdown Hills: National Park Study Centre, 5–10 Producing and Interpreting results of recent survey’, in Newman, P Dendrochronological Dates. London: EH (ed) Mining and Metallurgy in South-West Lynn, C J and McDowell, J A 1988 Britain, 27–34 ‘A note on the excavation of an Early Christian period settlement in Deer Fell, V 1993 ‘Examination of four Iron Age Park Farms, Glenarm, Co Antrim, ferrous hammer heads from Bredon Hill Hadman, J and Upex, S 1975 ‘The 1984–1987’. J Glens Antrim Hist Soc (Hereford and Worcester), England’. Hist Roman settlement at Ashton near Oundle’. 16, 2–16 Metall 27, 60–70 Durobrivae 3, 13–5

Fell, V and Salter, C 1998 Halkon, P and Millett, M 1999 Rural Manning, W H 1991 ‘Blacksmiths’ tools ‘Metallographic examination of seven Iron Settlement and Industry: Studies in the Iron Age from Waltham Abbey, Essex’, in Oddy, W A Age ferrous axeheads from England’. Hist and Roman Archaeology of Lowland East (ed) Aspects of Early Metallurgy. London: Metall 32, 1–6 Yorkshire. Leeds: Yorkshire Archaeol Soc BM Press, 87–96

29 Margeson, S 1993 Norwich Households: Ottaway, P 1992 Anglo-Scandinavian Starley, D 1999 An Evaluation of the The Medieval and Post-medieval Finds from Ironwork from 16–22 Coppergate. The Ironworking Site of Sherracombe, Devon. Norwich Survey Excavations 1971–1978. Archaeology of York 17/6. London: CBA Ancient Monuments Lab Rep 16/99. Norwich: Norwich Survey (East Anglian London: EH Archaeol 58) Owen, J (ed) 1995 Towards an Accessible Archaeological Archive. Soc Mus Archaeol Matthews, K 1999 ‘Familiarity and Timberlake, S A 1991 ‘New evidence contempt’, in Tarlow, S and West, S (eds) for early prehistoric mining in Wales – The Familiar Past: Archaeologies of Later Penhallurick, R D 1997 ‘The evidence problems and potentials’, in Budd, P, Historical Britain. London: Routledge, 155–79 for prehistoric mining in Cornwall’, in Chapman, B, Jackson, C, Janaway, R. Budd, P and Gale, D (eds) Prehistoric and Ottaway, B (eds) Archaeological May, J 1996 Dragonby. Report on Excavations Extractive Metallurgy in Cornwall. Truro: Sciences 1989. Oxford: Oxbow, 179–93 at an Iron Age and Romano-British Settlement Cornwall Archaeol Unit, 23–33 in Lincolnshire. Oxford: Oxbow Tylecote, R F 1986 The Prehistory of Photos-Jones, E, Atkinson, J A, Hall, A J Metallurgy in the British Isles. London: McDonnell, J G and Ottaway, P 1992 and Banks, I 1998 ‘The bloomery mounds Institute of Metals ‘The smithing process’, in Ottaway, P Anglo- of the Scottish Highlands. Part 1: The Scandinavian Ironwork from 16–22 archaeological background’. Hist Metall Tylecote, R F and Gilmour, B J J Coppergate. Archaeology of York 17/6. 32, 15–32 1986 The Metallography of Early Ferrous London: CBA, 480–85 Edge Tools and Edged Weapons. Oxford: BAR Pickin, J 1990 ‘Stone tools and early metal Mighall, T, Blackford, J J and Chambers, mining in England and Wales’ in Crew, P F M, 1990 ‘Bryn y Castell – late Bronze Age and Crew, S (eds) Early Mining in the British Vernon, R W, McDonnell, J G and clearances or climatic change?’. Archaeology Isles, Maentwrog: Snowdonia National Park Schmidt, A 1999 ‘Medieval iron and in Wales 30, 14–6 Study Centre, 39–42 lead smelting works: a geophysical comparison’, in Pollard, A M (ed) Mills, A and McDonnell, J G 1992 Geoarchaeology: Exploration, Environments, The Identification and Analysis of the Richards, J D 1993 The Bedern Foundry. Resources. London: Geol Soc, 15–34 Hammer Scale from Burton Dassett, The Archaeology of York 10/3. London: CBA Warwickshire. Ancient Monuments Lab Rep 47/92. London: EH Wainwright, G J 1979 Gussage All Saints. Salter, C and Ehrenreich, R 1984 An Iron Age settlement in Dorset. London: Mook, W G and Waterbolk, H T 1985 ‘Iron Age iron metallurgy in central HMSO Handbook for Archaeologists No 3: Radiocarbon southern Britain’, in Cunliffe, B and Miles, Dating. Strasbourg: European Science D (eds) Aspects of the Iron Age in Central Welsh Office 1996 Planning and the Foundation Southern Britain. Oxford: OUCA, 146–61 Historic Environment: Archaeology. Circular 60/96. Cardiff: Welsh Office Museums and Galleries Commission Scott, D A 1991 Metallography and [now adopted by the National Assembly 1992 Standards in the Museum Care of Microstructure of Ancient and Historic Metals. for Wales] Archaeological Collections Los Angeles: Getty Conserv Inst Wilthew, P 1987 ‘Appendix. Metallographic Scottish Office 1994a ‘Archaeology – the examination of medieval knives and shears’, Needham, S 1980 ‘An assemblage of Late Planning Process and Scheduled Monument in Cowgill, J de Neergaard, M and Griffiths, Bronze Age metalworking debris from procedures’ (Scottish Office Environment N Knives and Scabbards. London: HMSO, Dainton, Devon’. Proceedings of the Prehistoric Department Planning Advice Note: PAN 42). 61–74 Society 46, 177–215 Edinburgh: Scottish Office Environ Dept

Newman, J 1993 Three antler moulds from – 1994b ‘Archaeology and Planning’ Youngs, S M (ed) 1989 ‘The Work of Ipswich. Datasheet 17. Finds Research group (Scottish Office Environment Department Angels’ – Masterpieces of Celtic Metalwork, 700-1700AD National Planning Policy Guideline: 6th–9th Centuries AD. London: BM Press NPPG 5). Edinburgh: Scottish Office Northover, P 1987 ‘Non-ferrous Environ Dept metallurgy’, in Cunliffe, B Hengistbury Head, Zienkiewicz, J D 1993 ‘Excavations in Dorset.Volume 1:The prehistoric and Roman Sharples, N 1999 Scalloway: a Broch, Late the Scamnum Tribunorum at Caerleon: The settlement, 3500 BC–AD 500. Oxford: Iron Age Settlement and Medieval Cemetery in Legionary Museum site 1983–5’. Britannia OUCA, 186–96 Shetland. Oxford: Oxbow 24, 27–140

30 More copies of these guidelines can be obtained from English Heritage Customer Services: telephone 01793 414575 or 414576; address, Customer Services, National Monuments Record Centre, Great Western Village, Kemble Drive, Swindon, Wiltshire SN2 2GZ.

Please quote Product Code XH20166

Cover image Experimental iron smelting, using hand bellows (Photograph by Peter Crew) Compiled by Justine Bayley, David This guideline is published in association Dungworth and Sarah Paynter with the with Historic Scotland, CADW, the assistance of the Historical Metallurgy Environment and Heritage Service and the Society’s Archaeology Committee, with Historical Metallurgy Society. contributions by Peter Crew, Vanessa Fell, Brian Gilmour, Gerry McDonnell, Cath Mortimer, Peter Northover and David Starley.

Acknowledgements: This document draws heavily on the Archaeological Datasheets published by the Historical Metallurgy Society in 1995 and subsequent years. We are grateful to their authors for allowing their texts to be edited and republished in this new, expanded form. We would also like to thank all those who have commented on earlier drafts of this document.

Published February 2001 Historical Metallurgy Society Copyright © English Heritage 2001 Edited and brought to press by David M Jones Designed by Fox Design Consultants Produced by English Heritage Publications Printed by Sterling Press Limited

Product Code XH20166