Jormungand at Smeltfest
This is a preliminary report on the clay furnace that Dick Sargent and I built
and ran twice with good results at Smeltfest 06. This week long session was
held by Lee Sauder at his shop in Lexington VA over March 4 - 12, 2006.
A good week all round. We had five of us (Lee, Skip Williams, Mike McCarthy,
Dick and me) with Vandy Simpson and Elisabeth Sauder in support. We thus
broke into two teams. One team would prep a smelter while the other fired. The
next day we would switch the roles. This gave people a hard day followed by
an easier one. Much smelting accomplished!
Dick (foolishly?) followed my lead. Our intent was to accomplish three
1) Make some small changes to the Norse Short Shaft furnace that I had
used at Early Iron 1 and several times since.
2) Patch and re-fire the same furnace a second time.
3) Most importantly, test the hematite blasting compound that comes from
an industrial source fairly close by to my base in Ontario.
The furnace we constructed was christened 'Jormungand' by Vandy. This is
the name of the Viking 'world serpent'. Art got the best of me, the
serpent spews fire from its mouth on the completed furnace. (This proved
a lot of fun btw.)
From something I had wanted to try - and Skip encouraged, we used a
bundle of wood splits to create the inner form. This was based on
something Skip had seen Jake do when he was off in Holland a month back
visiting a smelting conference. The process of using withy / twigs /
straw in a bundle to shape the smelter, then burning these away at
preheat, I knew about from the archaeology. (Sorry to DARC - I know this
was on our experiment list). One other feature Skip suggested was to
taper the inside of the smelter so that the tuyere tip would be clear of
the top diameter of the smelter.
I found an ideal form - a two foot length of heavy reinforced stove pipe
at 10" diameter. The wood splints were off cuts roughly 1 1/2 x 1/2
thick. Over the lower pipe we laid a first circle of splints about 18"
long - held with duct tape. On top of that was a second circle, these
lengths fairly long, and latter cut off to about 34". Again a couple of
circles of duct tape held it together. The two layers created a tapered
shape - about 14" interior at the base and about 12" at the mouth.
Over this was plastered a layer of clay cobb. Lee had purchased a
quantity of standard potters 'ball clay'. He should comment on the
specifics and the price (It was something like $12 US per bag). The
smelter as constructed used about 2 1/2 bags of clay. This was mixed
about 50 / 50 by volume with straw, chopped down to roughly 3" long
lengths. As water was added * after * the first mixing, it proved
pretty easy to mix the material by hand. The cobb mix was applied to the
framework, roughly 3 1/2 inches thick at the base, tapering to about 2
thick at the top. Again at Skips suggestion, we pulled out a small lip
around the top edge. This widened the total external diameter at the top
to about 18". The reason was this (again from the European smelters) was
to make it a bit easier to add charcoal and serve as a bit of a fuel
The whole thing was set up on a concrete block plinth - constructed much
as we all did at Early Iron 2. The interior spacing for the plinth was
14 x 14 inches. The finished smelter had a total height of 30" above the
plinth. A small tap arch was created using three half bricks ** wrapped
in newspaper ** about 7 wide x 5 tall.
The tuyere was one of the high temperature pottery kiln supports that
DARC had experimented with last year. It has an OD of 2 inches and that
magic 1 inch ID. It was set about 2 inches inside the smelter interior
wall. The angle was the standard 22.5 degrees down that my team has
found effective (and was determined by the Gangue at Smeltfest 1). The
tuyere was set to 9 1/2 inches above the exterior base. When the normal
layer of tamped charcoal fines was added to the interior, this base was
about 2 inches thick. This put the interior tip of the tuyere at about
five inches above the base (measured from the centre point)
Once the whole thing had been constructed and allowed to relax for a
couple of hours in the sun, the metal pipe was carefully pulled up out
of the interior. The splint framework remained largely in place - the
longer lengths held by the clay. A fairly long drying fire was started.
The half bricks at the tap arch were pulled open to allow for air, and
the same wood splints were added and a fire kindled. This process
continued for several hours, with fresh splints added whenever the
material burned down. At the end of the evening, a circular metal cover
was placed over the top of the smelter. This was done mainly for fire
safety - but as it turned out may have had a profound effect on the smelt.
The next morning Dick and I showed up a bit early, as we didn't want the
smelt to run too late. (There was a good reason for this outta the house
by 7:30 thing at the time - but it escapes me now.) Because of the coals
inside and the metal cover, the smelter walls were still hotter than you
wanted to lay a hand on - and bone dry. We started the normal pre-heat
series of wood splits with natural draw for 30 minutes, 15 minutes with
gentle air blast, then a last 15 minutes with ungraded charcoal and
The air system was using my vacuum blower. Although this produces less
top end delivery than Lee's blowers (used at EI 2), it does have a
calibrated dimmer control that lets me estimate volume.
ON the first smelt, we STARTED at a charcoal consumption rate of the
standard 5 lbs every 5 minutes. The air blast was set for about 740
litres per minute. (For comparison, at Early Iron last year, the volumes
were about 1200 plus). For the first firing, the burn rate averaged from
5 - 9 minutes as we added ore.
The ore material was industrial hematite blasting compound. The stuff
comes in 90 lb bags at about $15 US per bag (At the plant in Ontario).
It is very consistent in size, screened for about 1 - 2 mm particles. It
is virtually ALL iron oxides - something like 90 - 95% worth. It is a
bit denser than the Virginia rock ore. We were using my normal long
handled scoop, which supplied 1 1/4 lbs per level scoop. At the peak of
the smelter operation, we were adding as much as FIVE scoops - a total
of 6 1/4 lbs of ore every 7 - 8 minutes.
On the first smelt, we added a flat 100 lbs of ore. There was a bit of a
problem near the end with what was most likely melted wall material
diverting the air flow. In the end the smelt took roughly six hours from
first fire to initial compaction of the bloom. We used 185 lbs of graded
Extraction was a combination of top and bottom. We let the charcoal burn
down to about half the smelter, then reduced air slightly and I scooped
the balance of the fuel out. I then used the log thumper to compress any
mother attached to the bloom and loose the bloom in the slag bowl. We
had earlier opened up the tap arch and plinth in an attempt to lower the
bowl. As it turned out there was very little liquid slag. (Not
surprising considering the purity of the ore). The end result was that
the thumping on the top just dropped the entire slag bowl mass down, and
the bloom came free very easily.
The resulting bloom was 48 lbs after knocking the loose mother off.
(That's a roughly 50% recovery of the ore weight). The material has a
sand like texture and is pretty crumbly. It did spark test out to a very
high carbon content. Also notable was a sheet of 'liquid steel' that had
formed and run down to deposit along the lower surface of the bloom. The
bloom proved forgeable - at least with great care. (I have to admit, it
took a lot of mistakes and some needed coaching by Lee for me to get the
hang of working this stuff.
See data03-06A.html for the experiment details.
So - we cleaned up the area, brushed off the loose clay and repaired the
For the second smelt (using the same furnace) we modified the area
around the tuyere. A new tuyere was used - as we had melted at least
half the first one (perhaps 4 - 5 inches).Again from something Skip said
he'd seen in Europe, we reinforced the walls around the tuyere.
Basically we created a cone of clay from the walls up to the end of the
tuyere. the material that was used for this was a different mix - one
that Mike and Lee were experimenting with. this was 50 % Ball and 50%
Kaoline grog, mixed with a volume of charcoal fines. This is a more
refractory mixture than the clay cobb.
We also changed the total height. From the first smelt, we had clearly
seen that the charcoal had only ignited up to 22 inches above the base -
16 inches above the tuyere. Higher than that the fuel might have been
heated, but was not com busting. There was damage to the top of the
smelter anyway, so we built up a new top flange at 24 inches total (so
about 18" above the tuyere). Other than that those two changes, the
furnace was laid out pretty much as it was the first time. We did have
to slap a fair amount of new clay into the area around the tap arch to
strengthen it. Generally, although cracked, the cobb was serving to hold
itself together well.
If anything, the second firing saw the Jormungand run even HOTTER - but
less consistently Even with the same air flow, occasionally the
consumption dropped to as little as 3 minutes for 5 lbs. The average
rate was 7 per charcoal charge. Because of the variation between
charging times, the average ore rate was five lbs per bucket. Because
the furnace came up to working temperature faster, in the end less
charcoal was used - a total of 150 lbs graded fuel.
Once again we added a flat 100 lbs of the hematite. The identical 'fin'
of obstructing material was observed at the tuyere near the end of the
smelt. This time we were more confident of the process, and merely
dropped the air rate for a couple of minutes to allow this to melt off.
Once again the extraction was a combination of clear the top, thump the
bloom free and pull out through a widened tap arch. The yield was very
close to the first smelt, this time at 44 lbs (with the loose material
knocked free). Once again the same combination of liquid steel plate
below a sandy textured high carbon bloom was the result.
See data03-06B.html for the experiment details.
The most obvious next step would be to combine the higher slag creation
Virginia ore with the high carbon producing hematite grains. The
hematite is a widely available commercial material (used for industrial
sand blasting) It is extremely consistent in both size and quality. This
may make it an ideal teaching and smelter development material.
(Edited from a posting to EARLY IRON Wed, 29 Mar 2006)
Text and photography ©
1998 - 2006, Darrell Markewitz