Conservator Sam van de Geer with a sword in Engin-X
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Neutron diffraction measurements can benefit the conservation of irreplaceable artefacts. A researcher from the Open University has used neutrons to study twenty-three Early Medieval iron knives and swords found at the local Early Anglo-Saxon (5th-6th Century AD) burial ground at Watchfield, Oxfordshire. The cemetery population may well include the first generation of Anglo-Saxon immigrants to settle in this area from the Continent. The objects were loaned for analysis by Oxfordshire County Council. Data gained from these experiments will benefit the conservation of the objects which, like all early iron artefacts, will deteriorate rapidly and irreversibly if not constantly monitored, treated, and stored appropriately.
Archaeological scientist Dr Evelyne Godfrey from the Open University, who is a specialist in early ironworking, and conservator Ms Sam van de Geer from Oxfordshire County Council, spent three days on Engin-X using neutron diffraction to uncover the microstructural composition of the objects which have mainly been in storage since their excavation thirty years ago.
Dr Godfrey explains, “We are studying at the carbon content of the steel portions, such as the cutting edges, of the objects but also the phosphorus content of the preserved iron. Where the metal does not survive we are looking for the volume of the different corrosion minerals. We'll be able to better understand the technology and craftsmanship of the objects, and to plan for their conservation.”
The Watchfield cemetery was discovered during the construction of the A420 Shivenham By-Pass in 1983. Fifty burials were excavated, but around one hundred graves had already been destroyed by construction works and small-scale looting before the rescue excavation. There are estimated to be another hundred graves still in the ground; the site has been protected as a Scheduled Ancient Monument. Human skeletal remains and grave goods from the site were originally investigated from 1983-90, and published by Chris Scull in 1992.
“One complete pattern-welded double-edged sword and 18 knives were recovered in the 1983 and 89 excavations” explains Evelyne. “We have used Engin-X because it allows us to look at the steel composition non-destructively - without cutting a sample - and provides the right conservation environment for these fragile, irregularly shaped, irreplaceable artefacts.”
Neutrons non-destructively opening up heritage science.
Neutrons have allowed the team to analyse what is preserved inside the objects. Evelyne explains, “X-ray diffraction only reflects the surface and would not go through the thick volume of intact iron artefacts, but with neutrons we can analyse the metal under all the corrosion layers without any damage to the objects”
Digital x-ray imaging, carried out in Bristol at the Radiography Department, Glenside Campus, University of the West of England, was used to select the analysis points. Neutron diffraction was then used to analyse the composition of the patches of preserved metal. The next step will be to compare the neutron data from Engin-X with previously published metallographic samples and neutron data from other Early Anglo-Saxon and contemporary Merovingian knives and swords.
The Watchfield Early Anglo-Saxon Cemetery objects are currently on temporary display at the Oxfordshire Museum, Woodstock.
Evelyne says, "The land next to the cemetery, a Scheduled Ancient Monument, is currently subject to a development application to build houses, and is in urgent need of geophysical survey, to identify the extent of the burial ground and to locate the Early Anglo-Saxon Settlement of Watchfield."
Research date: July 2013
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