AMS 14C Dating of Iron Artifacts: Development and Application

Abstract

We have developed a prototype carbon extraction system for accelerator mass spectrometry (AMS) radiocarbon dating of archaeological iron remains by combusting them with a RF induction furnace. We have also successfully tested and used a method of carbon extraction from iron using a CuCl2 solution. Modifications to our carbon extraction systems and methods provide us acceptable performances; carbon yield is normally around 80% and the 14C background level is as low as 42-48 ka BP in 14C apparent age. We have also conducted an iron refining experiment to examine the sources for carbon 14C age derived from iron, using established AMS 14C dating and carbon extraction systems. Our refining experiment was conducted on iron slag, which are by-products formed during iron smelting methods in the 7th century AD, and using modern charcoal as fuel. The aim of the experiment was to determine whether original carbon characteristics in the original iron materials would be preserved, or if the carbon signature would be replaced to some degree by the modern charcoal. AMS 14C measurements on the refined iron yielded 14C ages equivalent to those of the modern charcoal fuel. The result indicates that the original carbon signatures in the iron slag from 7th century production was replaced completely by modern carbon used in our experiment. The experiment confirms the assumption that 14C ages on iron products are associated with the fuel source of the iron smelting or refining process. We also report on the dating of iron slag materials excavated from the Gennaitouge iron smelting site, where 14C dates were consistent with the age of the site estimated by archaeological evidence.