Mark Chapman wrote:
One issue I think that may still exist is that during the pre 1500 period,
iron was not melted in the bloomeries and thus the refining to reduce the
slag content was purely done by repeated forging and welding the billet.
From the contents of this thread it appears that many students of British
ironworking still think of preindustrial iron production in terms of the
old, and thoroughly misleading, division between bloomery (by which is
meant processes producing carbon-free iron by solid-state reduction) and
blast furnace (producing liquid cast iron). This is a parochial view, now
largely restricted to northern Europe. Those who read the world literature
on the subject realize that this binary classification simply doesn't
correspond to historical reality. "Bloomery furnaces" - better redefined as
small charcoal-fuelled furnaces blown by hand, water, or by natural draft -
are quite capable of producing liquid iron and liquid steel. John Percy,
who did read the world literature of his time, notes this in volume 2, part
3 of his Metallurgy, published in 1864, and there are too many subsequent
records of it from Africa, Japan and north America to be listed here.
Indeed even the Bradford crowd are now proposing that the very clean steel
edges documented on 8th-9th century knives from Anglo Saxon Hamwic were
produced by making cast iron in a bloomery, then decarburizing it to steel!
(I'm sceptical - it seems much more likely to me that the liquid steel that
they document was directly produced in a bloomery).
The main point, however, is that if cast iron is desired as the starting
point for wire-making, then it is quite possible, and indeed quite easy, to
make it in a "bloomery". The major problem in understanding the early
history of extractive metallurgy in Britain is that there are very few
excavated smelting furnaces relative to other areas. My own thinking on the
matter is that there probably wasn't much production, even accidentally, of
cast iron or cast steel in Britain until the Roman occupation because the
furnaces were so pathetically tiny and appear to have had only a single
tuyere. When combined with your dismal climate, these factors make for a
barely viable process, certainly not one conducive to the production of
cast iron. (As seen for example in Peter Crew's experiments, which had
horrifically high charcoal consumption to produce a small amount of bar
iron). Contemporary furnaces in Africa (middle to late first millennium BC)
were typically much larger (80-140 cm internal base diameter), seem to have
had multiple tuyeres, and have produced evidence of the production of steel
(both solid-state and cast) and cast iron - which is not to say that these
were the usual product. I think that when the evidence is in we will
probably find that the occasional finds of cast iron in Roman and later
times are attributable to the use of larger, better-insulated and more
reducing furnaces than were in use during the Iron Age.
David Killick
Associate Professor
Department of Anthropology
University of Arizona
Tucson, AZ 85721-0030
phone: (520) 621-8685
fax: (520) 621-2088
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