Sunday, September 30, 2007

Thanksgiving Smelt - Preparations

Today I went out to make use of the wonderful fall weather - and start preparing the smelter area for the experiment next weekend.

I managed to lift out the still fairly intact furnace from our last series and move it aside in one piece. This was pretty remarkable as that furnace had withstood five separate uses, including the spring double smelt. Although it was bloody awkward and damn heavy, I have placed it at the base of one of the small hawthorn bushes propped up in its original orientation so it can can be observed as it weathers. (The weathering of used smelters is another long range project that I am continuing to record.)

There was one major surprise found when I dug away the embedded bricks used to support the earlier structure. As the image I took of the discovery was badly washed out, I will report on that later (with a better image)...

The following small images show the work so far:

First the smaller bricks used to support the previous smelter were removed. After the furnace was lifted off, any remaining brick fragments and larger clumps of slag were dug out of the base area. The hole created was then backfilled with a mix of earth, sand, ash, small fragments of slag and some charcoal fines. This material was the debris remaining from the last smelt.

To clearly distinguish this lower level (basically just support, a layer of heavy brown paper was laid down over the area. I do not expect any liquid slag or excessive heat to penetrate down to this level. The paper allows clearly visible separation at the lower ground supporting the structure. At the same time should any hot liquid slag penetrate this far, the paper will not halt its downward movement.

A new artificial ground level was established above this. Raw earth from elsewhere in the yard was laid roughly level and compacted (using a brick as a mallet) to a depth of 10 cm. To contain this layer a line of heavy clay bricks was positioned just proud of the existing line of concrete blocks. This construction gives enough space to build up the stone front for the clay cobb cylinder of the smelter.

There are a number of flat stone slabs of various compositions and sizes on hand from earlier gathering trips. The current plan is to build up the body of the smelter on Saturday (October 6). Initial pre firing to stabilize and dry the clay will tale place into the evening, with finial preparations and the main smelt sequence on Sunday (October 7).

Friday, September 28, 2007

Towards an Icelandic Smelter (1)

(As background - Early Iron 4 was canceled due to lack of organization.
and I had already set aside time for it. So on short notice I decided to
run another smelt here at Wareham)

Dr Kevin Smith and I have been discussing the work he has been doing
excavating a Viking Age iron smelting site at Hals in Iceland. The
details can be found in his article 'Ore, Fire, Hammer, Sickle: Iron
Production in Viking Age and Early Medieval Iceland'.

A long range plan is to work towards a full reconstruction smelt using
the Hals excavations as the prototype. In brief the construction is a
conical stack of cut grass sod strips contained in a box frame of
timber. This whole construction is roughly 2 x 2 m and stands about 1 m
tall. The space between the cone and the box is leveled off with earth
for a working surface. The shaft of the furnace is cut down into the
sods, then lined with a relatively thin (3 cm) layer of clay like
material. The tuyere area is made up of stone slabs, with a 'blow hole'
method used to introduce the air. Evidence strongly suggests a top

Taking some information provided by Skip Williams from his experiences
working (primarily) with Micheal Nissen (from Ribe) at the last European
Iron Symposium:

The blow hole has a thin plate of material used in those areas of the
furnace around the tuyere that are subjected to the greatest
temperatures. The thinner plate around and especially above the tuyere
opening allow the heat to bleed off the surface and keep the plate from
melting. (This opposed to our current thick walled furnaces that
withstand erosion every smelt.) The tuyere itself does not fit tightly
into the smelter - or protrude into the inside of the furnace. (Our
current method does both of these.)

This blow hole method has proved successful (Nissen and Williams) at lower air volumes - in
the range of 300 litres per minute.
As the bellows tube does not extend into the furnace, there is minimal
damage to the tube. (In essence there is no true tuyere - just the
nossel of the bellows).
The opening for this bellows tube is larger than the tube itself. In
practice Skip reports this produces a venturi effect to increase air
flow. It also allows the operators to see directly into the interior at
the developing bloom. Any surplus slag will flow off well before it
clogs up the air blast.

I have decided to run the Thanksgiving smelt as the first test towards
the full Hals prototype:

The main difference here from our last smelter is the construction of a
stone slab front and use of the blow hole method. The overall
construction will remain the proven thick walled clay cobb set as half
buried in the earth bank. The tuyere / bellows tube will again be the
ceramic tube with air via the current vacumn blower. This blower can be
throttled back to the lower air volume.
There is plenty of charcoal on hand, most likely using the pre sized
material that the Wareham Forge purchased in the spring (to save labour).
As the evidence from Hals suggests a high iron content bog ore was used
(very little slag produced) I'm suggesting use of the hematite grit as
the ore. Carbon control may be a problem, but the smaller particle size
may prove a good fit to a reduced air volume.

In truth this amounts to THREE changes to our process: Tuyere / Plate /
Air. I don't anticipate too many problems from the use of the stone
plate construction. Air can be quickly modified if required. The use of
the blow hole rather than our standard insert tuyere is the main
modification here.

Still there is a good chance (I'd say at least 50 / 50) that the smelt
may not result in a working bloom.

(Stay tuned!)

Monday, September 17, 2007

Viking Age Seax Two

I may have talked about this blade earlier in the year - back in the forging process. The knife is completed and now off to the customer.

The blade is a heavy tool knife pattern - most typical of Norse men's knives. (Note that the customer is a woman - but one who specifically wanted the heavy tool style instead of the more typical long triangle kitchen blade.)

The overall length of the blade is a bit over six inches (these images roughly life sized - sorry that they are not the most crisp). At its widest (just back of the false edge) the blade is roughly 1 1/4 inch wide. The hilt is a natural piece of caribou antler. The wire wrap is a feature the customer requested. I drilled two small holes that the wire ends tuck into, then the strands were soldered together at top and bottom. (This was a high tin solder to avoid burning the underlaying antler.)

The blade is made up of 209 layers. The starting block was 13 layers :
M = 1018 mild steel at 1/8"
L = L6 alloy (.5 nickel and .5 carbon) at 1/16"
H = 1095 carbon steel at 3/16"
The overall carbon content is lower, with the bulk of the material being supplied by the mild steel. The inclusion of L6 is to mimic meteoric iron.
This pile was welded and folded in three for a billet at 52 layers. That billet was drawn to a bar, with a third twisted right, a third twisted left. The last third was flattened and pulled out to twice that length, then welded to a second core of high carbon steel. The resulting bar was turned on its edge, and the two twisted segments welded into the final billet. This billet at 209 layers was forged out into the blade.

The finished blade is ground back at the edge to expose this high carbon steel cutting edge. This edge is hardened a bit more than normal for a plain mono block knife, as the layered back adds the required flexibility for the final blade.

February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

COPYRIGHT NOTICE - All posted text and images @ Darrell Markewitz.
No duplication, in whole or in part, is permitted without the author's expressed written permission.
For a detailed copyright statement : go HERE