AMS radiocarbon dating of rusty iron

The role of rust in the radiocarbon dating of iron artefacts has been examined experimentally. This was accomplished by re-measuring, using modern accelerator mass spectrometry techniques, the radiocarbon dates of ancient iron-based artefacts that were originally radiocarbon dated 30 years ago by beta counting. The samples were dated with the rust that had accumulated over the last 30 years, which in some cases had consumed most of the original metal. The study also afforded the opportunity to compare beta counting with accelerator mass spectrometry, large and small sample sizes, and old versus new carbon extraction methods. The results demonstrate that in at least some circumstances the carbon in rust can be reliably used for radiocarbon dating. Some experimental observations on iron microstructure and oxidation processes which support these results, are reviewed. The issues of sample size and the role of rust are important because they open up new possibilities for dating iron-based artefacts that had previously been assumed to be unavailable. (C) 2002 Elsevier Science Ltd. All rights reserved.