The Technology Team provides advice on all aspects of archaeotechnology including materials and artefact analysis, as well as using its specialist expertise to contribute to Archaeology Commissions Programme projects. Many of these produce evidence for metalworking, and the identification of this debris and its relationships to excavated features helps illuminate settlement structure and economy.
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The value of routine chemical analysis of debris was highlighted when material from the Roman site at Killigrew Round, Cornwall, was found to contain tin. Whilst the site requires further study, these initial results may signify early tin smelting. Elms Farm, Heybridge produced surprisingly little Roman metalworking debris but this did include a rare find of an iron bloom, at 12.5kg the largest known from this country. Another small assemblage, from Housesteads Fort, provided rare, unambiguous evidence for the use of coal in Romano-British iron smithing. Study of two large and unique groups of clay piece-moulds from Castleford, Yorkshire, has been completed. This shows that enamelled flasks were made there in the late first century AD and purse-shaped spoons in the third century. In the illustrated mould the right hand piece shows the runner through which the metal entered the mould, lugs to correctly locate the two pieces of the mould, and the raised patterns which produced recessed fields in the metal castings that were then filled with enamel.
The assessment of metalworking debris from No 1 Poultry, in the City of London (see also section 4.9), showed iron-smelting and smithing were accompanied by some copper alloy-melting and lead-casting. Many of the bulk iron-working slags came from Roman levels but micro-slags (hammer-scale) were common in medieval contexts so the site promises an interesting comparison between their distribution and excellent documentary evidence for thirteenth-century iron-smithing and ironmongering. Another medieval site, Norwich Greyfriars, produced evidence for silver refining as well as the melting of a range of copper alloys and the casting of substantial copper alloy objects such as bells or cauldrons.
The examination and analysis of finished objects has covered a wide range of artefacts, periods, and geographical regions. A wide range of decorative finishes was identified on a group of plated and inlaid medieval ironwork from York; the most unusual was the mercury-gilded silver wire inlaid in complex patterns in two knife blades. The metallographic analysis of knives and spearheads from the Saxon cemetery at Boss Hall, Ipswich showed the surprising use of pure, soft iron for the spearheads, compared with the more usual practice, seen in most contemporary edged tools, of incorporating hardenable steel.
Two geophysical techniques are being investigated as means of locating and identifying evidence for iron-working. Magnetic susceptibility is being used as a method of rapidly quantifying magnetite-rich hammer-scale in soils from a range of sites. The response of a fluxgate magnetometer to this and other types of iron-working debris is being investigated in conjunction with Archaeometry Team; a pilot study at Sherracombe Down, Exmoor successfully demonstrated the very intense magnetic fields generated by furnace debris.
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A large group of broken Roman rotary querns from recent excavations at No 1 Poultry, City of London are currently being studied. This assemblage is without parallel in Britain or indeed western Europe; there are at least 1,000 fragments, many occurring as large segments of upper or lower stones. They all come from within a small area of the site, a cobbled surface constructed between AD 70-90. The majority of the querns are dark grey vesicular lava and came from the Mayen area of the Eifel Hills of Germany; differences in their texture may reflect use of different parts of the lava flow. This find is of particular importance, for its size and because querns are not normally found in such closely dated contexts. There is also the question of how the assemblage should be interpreted. The broken querns might represent ship's ballast, they could imply a nearby mill or large bakery, or they could be debris from an importer's or millwright's yard where querns were brought for recutting. A study of the tooling marks and use-wear will help answer these questions. The opportunity will be taken to compare this assemblage with other Roman and Saxon lava querns in this country.