Issue 111

Mar / Apr 2010

Contents

news

New centre for Stonehenge – if drivers agree

British archaeologists help record Armenian rock art

Geophysics finds encourage new look at Stanton Drew

Dramatic rock art discovery in Swaledale

in the press

in brief & phase 2

features

The Future of our Past (not online)

In the run-up to the General Election, the parties give their views on heritage

410–2010: Rome and Britain

Introducing the events and issues commemmorating 1600 years since the end of the Romans in Britain

THE BIG DIG: Barcombe Roman Villa

What was it like to live in rural Roman Britain? Report on 11 seasons of fieldwork at the villa and bath house

Polynomial texture mapping for archaeologists (not online)

A new imaging technique is relatively easy and cheap to operate, yet has enormous possibilities in archaeology

Introducing Stonehedge and other curious earthworks

Stonehenge is the focus of unprecedented research. Yet the site was last surveyed in 1919, until now...

Remembering Fromelles

One of the most pointless battles of the First World War, with great loss of life, occurred at Fromelles in northern France. Only now are some of the dead being honoured with individual graves

on the web

Caroline Wickham-Jones looks at e-material

Adrian Green describes the new website for Salisbury Museum

science

Sebastian Payne considers the remarkable potential of hammerscale for understanding the work of iron smiths

requiem

A tribute to some of the archaeologists and lovers of antiquity who died in 2009

letters

your views and responses

CBA Correspondent

Mike Heyworth considers the thorny issues of treasure and responsible detecting

ISSN 1357-4442

Editor Mike Pitts

Science

The shadow in the old smithy

Sebastian Payne, chief scientist at English Heritage, considers the remarkable potential of hammerscale for understanding the work of iron smiths.

When sparks fly in a smithy, they end up on the floor as "hammerscale" – tiny pieces of iron oxide or slag, as much as half the iron produced in bloomery furnaces. As recent studies show, they can tell us a lot about past iron production and working.

Until around 1500, iron was made in England by the bloomery process. Ore is heated in a charcoal-fuelled furnace to reduce the iron oxide to iron, and melt the other minerals so that they run off as slag. This produces a "bloom" – a large spongy mass of iron and slag. The bloom is heated and hammered to drive out the slag and make workable iron billets. This produces mainly two types of hammerscale: flakes, usually several millimetres long and rather over half a millimetre thick, and spheres, typically 1–5mm in diameter. Early in the process hammerscale has a high proportion of slag; towards the end it has much a higher iron oxide content.

Smiths then heat the billets and turn them into whatever is needed – nails, horseshoes, swords and ploughshares – and these again are heated whenever they need to be repaired. This shaping produces more hammerscale: iron is a reactive metal, and when heated the outer surface oxidises, and as iron oxide is brittle, it flakes off. The flake hammerscale from this "secondary" smithing is thinner and darker than that from the bloom hammering; it sometimes has a bluish-black metallic surface because it is mostly iron oxide. Spheres are also produced, probably mainly when two pieces of red hot iron are hammered to "fire-weld" them.

Surprisingly, though iron artefacts present conservation problems, hammerscale preserves well in the archaeological record. As it contains magnetite, concentrations show up well in geophysical surveys, and fragments can be extracted from sieving residues with a magnet. Recent work on a Viking period workshop at Viborg Søndersø in Denmark shows the kind of results that can be obtained by looking at the distribution of hammerscale and related materials.1 The workshop, built shortly before AD1020 at about the time Canute was crowned at Viborg, was a wattle-built 5mx3m shed. During its main period of use it had a raised hearth at the north end. Hammerscale concentrates near the south end of the hearth, round a pit which held the base of the anvil; an area with less hammerscale (circled in the diagram above) is probably where the smith stood – his apron deflecting the sparks. Another area with little hammerscale on the west side of the hearth is probably where the bellows stood. In a slightly earlier context, a large concentration of charcoal fragments suggests that the charcoal was stored in the south-west corner of the workshop, in a bin; a zone of crushed charcoal and hammerscale marks the "footpath" of the smith between this and the anvil, and a hammerscale concentration suggests that iron billets were stored in one corner of the bin. Interestingly, slag analyses suggest that the iron was imported from central Europe.

Thanks for all their help to Justine Bayley, David Dungworth, Arne Jouttijärvi, Sarah Paynter and David Robinson.

More science

1. A Jouttijärvi et al, in ed M Iversen et al, Viborg Søndersø 1018–1030 (Viborg 2005); "The shadow in the smithy", by A Jouttijärvi, Materials & Manufacturing Processes 24 (2009), 975–80
2. S Paynter, in Historical Metallurgy 41 (2007); J Bayley et al Archaeometallurgy (English Heritage 2001)

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