On 28 Jan 2003 at 16:14, John L. Berry wrote:

> All of which leads to MY question:   does anyone on the list know (or
> know someone or some book who knows) quantitatively what the inputs
> (FeOx+carbon) and outputs (Fe metal plus slag) would have been for iron
> age bloomeries such as these?  In my calculations referred to above I
> had to make a lot of assumptions that I would like to refine.
>
John

We (myself and Gary Thomas, a recent PhD student) have done
quite a bit of work doing mass balance modelling for Romano-British
and Medieval bloomery working of iron oxide ores around the Bristol
Channel.

To summarise the results we found the following mass balance
would be a typical of bloomery operations of Roman age employing
a goethite ore:

1 kg of anhydous ore (or 1.1kg goethite) would react with 0.2kg of
furnace lining and 0.02kg fuel ash, to produce 0.4kg iron and 0.69kg
of
slag (ie 54% of iron in the ore was converted to metal)

In our examples, the typical weight of slag per smelt seems to be
around 6-8kg, so it would seem that around 4kg of iron ought to be
being produced per smelt. Exactly how much of that was in the
bloom and retrievable is unclear. We have billets of 1.5 - 2.5kg and
experimental studies suggest 50-65% of iron in the raw bloom
makes it into
the billet - so this tallies with raw blooms approaching 4kg.
Experiments
also suggest a yield of bar iron of about 50-60% of the billet - so our
billets would have yield in the range 0.8 - 1.5kg bar iron.

So we get an overall equation of 1kg of finished bar iron being
derived from 11kg goethite, with the production of 7kg of smelting
slags and at least another 7kg of smithing slags.

As a comparison, late medieval furnaces with similar ores were
winning around 75% of the iron in the ore into the bloom - and
producing raw blooms of over 50kg!

hope this helps

Tim



The references are:

Thomas, G.R. 2000. A chemical and mineralogical investigation of
bloomery iron-making in the Bristol Channel Orefield, UK .
Unpublished PhD Thesis, Cardiff University.

THOMAS G.R. & YOUNG, T.P. 1999. Bloomery furnace mass
balance and efficiency. In: A.M. Pollard (ed) Geoarchaeology:
exploration, environments, resources, Geological Society of London,
Special Publication No. 165, 155-164. [ISBN 1-86239-053-3]

THOMAS, G.R. & YOUNG, T.P. 1999. A graphical method to
determine furnace efficiency and lining contribution to Romano-
British bloomery iron-making slags (Bristol Channel Orefield, UK).
In: Young, S.M.M., Pollard, A.M., Budd, P. & Ixer, R.A. (eds) Metals
in Antiquity. British Archaeological Re Archaeological Reports
International Series, 792, 223-226. Archaeopress, Oxford. [ISBN
84171 008 3]



--
Dr Tim Young
Email: [log in to unmask]
Web: www.geoarch.co.uk
Phone: 029 20747480
Mobile: 07802 413704
Fax: 08700 547366