Dear Tim,
The overall structure illustrated would not seem to be typical of RB
British iron. The density of slag inclusions is unusually high, and the slag
morphology is unusual (that is forgetting about the two different
classes of inclusions). I have seen similar in over-heated metal (both from
archaeological sites and and from my own failed welds), but these were
produced using charcoal as a fuel.
The arrange of inclusions and the contact between the metal and the
slag all suggest that this metal has not been forged to any extent since the
inclusion structure has developed. This would not be surprising if the metal
has picked up sulphur, as the presence of any significant amount of sulphur
without compensating manganese will result it a very hot short metal. (The hot
shortness being due to the fact that iron sulphide form thin low melting point
films on the grain boundaries - there is some evidence for this on the lower
magnification image.)
How far are your results from stiochiometry, and which of the two iron
sulphur compounds pyrite or troilite? The latter is the more likely. What are
the other elements present, of particular importance are the amounts of oxygen
(if you have a light element detector), calcium and potassium?
As for comparative data, I have not seen similar 'sulphide' structures
in any Iron Age (several hundred pieces) or RB iron artefacts (a rather small
number), but have in some late 19th century/early twentieth century smithing
waste material. I have seen the very occcasional sulphide Fe/Mn - oxy-sulphides
in some smithing debris from RB smithing sites where coal was used.
My suggestions as to the mode of origin would be either that it was a result of
completely over-heated weld using coal as the fuel, or some was attempting to
smelt using coal. The latter being very very VERY unlikely unless you are
finding a lot of this material.
Chris Salter
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