Dr. Evelyne Godfrey with an iron spearhead from the Early Medieval cemetery site of Rhenen (the Netherlands), from the National Museum of Antiquities, Leiden.
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The study of ancient artefacts is complicated by the desire not to change or damage the objects in any way. One of the benefits of using neutrons to investigate materials is that they are both penetrating and nondestructive. These properties are now enabling their use in the study of historic items, revealing information relevant to object provenance and authenticity
Archaeometallurgist Evelyne Godfrey and diffraction specialist Winfried Kockelmann have employed neutron analysis to help them to uncover some ‘forged’ iron artefacts. Using neutron diffraction techniques, Godfrey and Kockelmann examined the surface corrosion and mapped the carbon composition of what was thought to be a set of Roman carpentry tools. In Roman times these kind of tools were normally made with hard steel working edges, which means they should contain an iron-carbon compound called ‘cementite’.
Visual examination of the tools immediately raised suspicions that both the shape of the objects and the appearance of the corrosion were not consistent with previously investigated, well-provenanced, examples of Romanera iron tools. Neutron diffraction at ISIS showed that all three objects were in fact made from carbon-free soft iron rather than steel, and that even the working ends had no cementite and were not heattreated. The objects were pure iron, and did not appear to have been functional tools. In addition, the surface corrosion did not match the diffraction patterns usually seen in archaeological iron artefacts.
Godfrey and Kockelmann concluded that these tools are unlikely to be ancient. They could well be modern – late 19th or early 20th century – wrought iron tools that have been corroded to resemble archaeological artefacts.
There is no direct scientific method that can be used for dating pure iron objects. Carbon-14 dating, for example, has been applied to high-carbon steel and more successfully to cast iron, but is of no use with low-carbon and pure iron. A combined analytical methodology, including neutron diffraction, could now provide the prospect of distinguishing authentic early iron artefacts from forgeries that may have long since been accepted in museum collections. Further development of neutron imaging capabilities may enable production of three-dimensional chemical composition maps of objects.
Evelyne Godfrey, Winfried Kockelmann (ISIS)
Research date: December 2004
W Kockelmann et al, Physics Education, 2004, www.iop.org/journals/physed
ANCIENT CHARM is a collaboration seeking to further develop neutron techniques for analysis of archaeological objects. Further details can be found at http://ancient-charm.neutron-eu.net/ach/
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