>To the medieval smith all iron was wrought
> iron and so described if he even used the term wrought.  With no
> understanding of metallurgy he could not make iron with phosphorus by intent
> and thought steel was purified iron.

        There might not have been a written terminology for the different kinds
of iron, but it is very clear that the Saxon smith knew the difference between
steel, low carbon iron and phosphoritic iron. The analytical work carried at
Oxford for Brian Gilmour on pattern-welded blades of the 6th to 9th century
show the deliberate use of alternate high and low phosphorus metal for the
pattern-welded decorative core and high quality and relatively uniform steel
for the cutting edges.

Clearly, they did not know the which elements were altering the properties of
the metal but they were using the metal as effectively as if they did, by
selecting the metal by test or by source.

        Going back to the Iron Age you can see how selction by source was
possible over large distances. The various shapes of the iron trade bars, each
coming from a specific region, if not smelting site, tend to have compositions
reflective of the ore used and the manufacturing process. The hoards are
typically of one type with high phopshorus bars coming from the Jurassic ridge
and similar ores, other narrower forms are low carbon, others tend to have high
carbon contents.
        At Danebury, there were cut bars of various form present on site, and
it was clear that the smiths were selecting metal for specific uses.

        There may be a similar pattern of different shaped billets from the
Saxon and later periods, but because of the lack of 'ritual' deposition of
whole bars it has not been possible set up such classification. The development
of a scheme of classification is not helped by the way in which the surviving
cut fragments of trade bars and billets are usually ignored in the site reports
- unillustrated and referenced as other 'unidentified' fragments.


> I will admit this has led to some
> confusion on my part in trying to determine how "refined" the iron needed to
> be for maille.

The term refined is is misleading - as it implies that by working the metal the
smith will improve its qualtiy in some way. This is not necessarily true. Some
blooms and billets (both experimental and archaeological), particularly those
with higher carbon content seem to have a much lower slag inclusion density,
than phosphortic and low carbon iron. (This I don't understand as yet).

        Looking at a Roman piled object this week, as well as a number of
other Roman objects from the same period (45-70AD) it is clear that the majority
of the slag inclusions had been introduced during the welding stage. It the
working regions of the blades those the smelting slag inclusions, of which
there were few, had been broken down to 1 to 2 microns diameter. At this size
and density, they would not have any significant effect on the drawing
properties of wire for mail other than a slight increase in the
work harding rate (unfortunately there was no surviving mail from any of these
sites). But of course the metal has to work harden appreciably if you are going
to pull it through a draw plate rather draw it down by hammering.

        This means that the properties of the metal will depend on the skill of
the smith as much as the metal itself. An incompetent smith can ruin perfectly
good metal by introducing a high slag density.

        Another example of this was in a series of experiments I have been
associated with it was attempted to draw down the flanges to make the sockets
of Iron Age trade bars from high phosphorus iron. Not being a competent smith
at the time, the experimenter got a series of artist blacksmiths to attempt the
operation. Most smith pronounced that the metal was useless, as it cracked when
working the thin sections. Often ruining a substanial section of the rest of
the bar in the process. It was only when the nth smith, n > 5 , n <10, was let
loose was the metal thinned to the same degree as the original. He pronouced
that it was excellent metal to work with! But then he had been working with
high phosphorus metal for 20 years!

        At that point I finally gave up believing what the textbooks said about
phosphorus and iron. This is only one of a number of cases I have found, where
where my metallurgical training says that the microstructure, compositon and
form of the artefact were incompatible. Given time and effort in analysis and
experimental reconstruction you can eventually work out how the near impossible
was done, with no instrumentation.


Chris Salter
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