DARC Iron Smelting Series - Experimental Philosophy

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!).

Focus:

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.

Smelter Design:

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.

Air Delivery:

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 pressure).
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.

Ore:

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 product).

Charcoal:

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).