Iron Smelting Series - Experimental Philosophy
The following notes cover discussions and decisions made by the primary smelt team
of DARC during the smelter prep on May 15, 2004. These follow up on the earlier list
of 'Limits of Experiment' that described the wide range of variables that effect
these iron smelts. Valuable observations were contributed by Kevin Smith of the Haffenreffer
Museum of Anthropology (with much thanks!).
One major decision was to define our objectives for this series of experiments.
One possibility is to concentrate on PRODUCTION - the successful creation of a useful
iron bloom. The obvious direction would be to duplicate the equipment and process
used by Lee Sauder and Skip Williams of Virginia (Colonial with modern modifications).
This system gives proven results, plus we have both detailed notes and direct observation
of the process working. It was decided by the group that this would take us further
away from our original focus on the Viking Age.
One possibility is to concentrate on PROCESS - the successful reconstruction of Viking
Age smelting equipment. The direction here would be to duplicate historical types
as closely as possible, then work with them to get positive results. This process
of continued experiments is sure to prove considerably more difficult because of the large
number of potential variables.
A major factor to consider was the past activities and strength of DARC - that
of presenting living history to the general public. There are many reasons why
the group is not able to operate as a pure research level (limited time available,
lack of funding, and poor access to research sources primarily). On the other
hand, there are few other groups with as much direct experience with effective
public demonstrations. It was noted that there are two upcoming presentations
by DARC of iron smelting (CANIRON in August 2005 and potentially Haffenreffer
in September 2005) - both as living history demonstrations.
The final decision of the group was to stress developing a historically accurate
physical presentation. This will entail focusing equipment towards Viking Age
types. The participants will aim to develop direct experience in operating this
equipment, and hopefully positive results will come as our techniques improve.
Also under consideration was the potential to generate 'new knowledge'. From some
observation of other experimental teams and suggestions by Kevin Smith, it would
appear that DARC may be able to provide the following information from its experiments:
1) The effects of weathering on 'used' smelters over time.
2) The effective method of utilizing the double bag bellows.
In the case of the weathering data, it was decided to build a series of identical
smelters which would be allowed to degrade over time, with observations and samples
taken on a regular basis.
Some consideration was given to possible overall designs of potential smelters.
One important factor in the design chosen remains the use of locally available
(free) materials for the construction. Largely based on information contributed
by Kevin Smith, the basic design of the 'boxed short shaft' was chosen. The interior
is a slightly tapering cylinder with a base diameter of about 25 cm, and interior
height of about 60 cm with a wall thickness of about 10 cm. The walls are constructed
of the local red clay, with some chopped straw and sand added (this mixture proved
structurally strong in 2003 smelter). The air inlet will be located about 10 cm
above floor of smelter. A slab stone 'box' about 40 cm tall supports the base
of smelter with the gap between box and cylinder filled with course sand.
In keeping with past experience a cylindrical sheet metal form was used to define
the interior shape (then removed). A section of 2" dia heavy steel pipe would
reinforce air inlet. The clay liner would be constructed well in advance of the
experiment and allowed to air dry for some weeks.
We have three possible mechanical systems:
First is the electric blower we used last year. It delivers high volumes, and can
be predictably (if roughly) modified for flow. Its main disadvantage is the relatively
low pressure, which is constant.
Second is a hand cranked 1800's style forge blower. There are several of these,
some that deliver a large volume of air. This is the least desirable option as
it has the disadvantages of both other systems (operator inconsistency plus low
Third is a small mobile compressor that we could rig as the air delivery system. This
would provide good volume - and lots of delivered pressure. It has a basic pressure
gauge, so we could modify and record the pressure. Not entirely sure that the volume
would vary (save as a function of pressure).
The use of a reconstructed double bellows presents one primary problem - maintaining
consistent air delivery through fatigue and switching operators over the 4 - 5 hour
course of firing. Its advantage is the ability to quickly modify both delivery volume
and pressure. (Plus conforming to the historic type).
In keeping with the overall goals of our experiments, it was decided to
use the reconstructed double bag bellows.
The overall set up of the equipment will be similar to last year - that is a 'T'
fitting on the actual air inlet tube. The smelter wall is fitted with a larger
piece of heavy steel tube, with the 1 inch diameter inlet pipe inserted into it.
This allows for changing the relative entry angle of the air blast. The resulting
gaps would be sealed with clay. The bellows will attached to the offset arm of
the T, conducted through a short length of flexible tubing. The straight arm of
the T is capped with a removable fitting with an transparent port. This will allow
for direct observations and temperature measurements with the optical pyrometer.
Should clearing the air flow be required, a metal rod can be inserted. It was
felt that this modification from the original period straight line arrangement
did not significantly change the operation of the bellows.
One important piece of data we need is some way of recording both air
volume and pressure. Rough volume figures could be determined by timed
filling of garbage bags (gives a simple volume / time ratio). Pressure
on the other hand requires some instruments. Some inquiries will be
made to see if anything on hand can be adapted, and checks made to see
if something can be purchased with the limited budget.
A major factor remains the difficulty in securing a dependable supply of consistent
raw iron ore. Past experiments were conducted with 'enriched' bog ore (2002) and
Virginia rock ore (2003). Lee Sauder generously supplied about 150 lbs of rock
ore in fall 2002, there is about 100 lbs of this material remaining (enough for
roughly two more smelts). A good deal of discussion was undertaken about how to
secure an Ontario source for actual bog ore, and the possibility of manufacturing
a 'bog ore analog'.
The final decision was to continue using the Virginia rock ore. Despite
the fact that bog ore would be the most correct historic type, the use
of the rock ore will provide a consistent material over several smelt
experiments. In addition, everyone agreed that efforts should continue
into finding a bog ore source - closer than L'Anse aux Meadows!
Specific individuals will be undertaking research, based on their
personal resources. (Kevin via the MNR / Gus via analog development /
Darrell via museum contacts). One useful suggestion was the development
of a manufactured bog ore analog that might be a useful substitute
during public demonstrations (where process is featured more than
There is enough charcoal from the original Royal Oak donation to fuel one more
firing on hand. Obviously continued experiments / demonstrations will require
another source. A number of potentials were considered: manufacturing our own
/ another (Canadian) sponsor / direct purchase. Some background research into
alternate charcoal types, and the theoretical relationship between smelter volume
/ ore size / charcoal size will be undertaken (Gus).
Text and photography ©
1998 - 2007, Darrell Markewitz