Sometimes a Great Notion (Icelandic Furnaces)

Q : 'Can the Hals Icelandic furnace build be re-used after three winters of weathering?

Well - kind of...

In consideration of the upcoming November 3 (Sunday) bloomery iron smelt at Wareham, Neil Peterson and I decided to return to the 2021 furnace that was a full build of the sod cone with thin clay lining as used at Hals, Iceland. This furnace had suffered considerble damage from both the extraction process and the intervention of a snapping turtle (!) after the June smelt that year. The front section was repaired and it was fired again in September. At that point major cracking resulted in the failure of the front wall section, with a wide band of loosely fused dirt in that area. (see https://warehamforgeblog.blogspot.com/2021/09/replacements-and-improvements-smelter.html )

The structure has been exposed to the weather since that point. Rain had washed loose earth into the interior and out the open front, and caused the supporting sods to slump down. Freeze and thaw had eroded the upper portions of the fused clay liner, and widened many cracks. The still mainly intact liner had slumped forward through about 25 degrees off vertical.

 The remains of the furnace, wild grasses trimmed off the sod cone. Front extraction side forward

Stick follows the line of the inner furnace surface.

Cracked and flaked away surface of the upper portions visible

Neil Peterson and I attempted to dig it clear of collapsed soil and set it back to vertical yesterday.

Not so much! The fractured liner broke into two larger and a number of smaller pieces 

Broken after our attempt to straighten the liner, the two larger pieces each about 1/4 of the original.
 

Working on the impression that will little clay available, Icelanders would attempt to keep what they had and patch it back together (??) this is what we did. 

The missing front section was replaced with on hand stone blocks, setting a ceramic tube tuyere. The previously used basalt lintel stone was set above this to support the upper blocks. From the tuyere line upwards gaps between the blocks were sealed with fresh clay.

The completed replacement for the front section, now all stone blocks.

As much as possible, remaining pieces of the fused inner liner were patched together, gaps and cracks sealed with fresh clay. The clay used is the Icelandic clay analog mix, based on samples obtained by Michelle Hayure-Smith, and suggested by team member Marcus Burnam (see https://warehamforgeblog.blogspot.com/2021/06/sticking-to-it-clay-mix-for-icelandic.html) A very rough calculation was made of the clay required = about 2.5 litres (as a plastic mix).

Image into the interior, showing the lower rear and left side surfaces. Fresh clay is dark grey.

Two wooden sticks were driven down to help support the wall pieces as they were sealed in with fresh clay. It is expected there will be further cracking between the old and new surfaces as that applied clay dries and shrinks. There should be a second repair made to ensure new cracks are sealed before firing. This was a step not taken between the previous two uses, thought to be why there was a major burn through in that earlier front wall section repair.

A circle of stone blocks was added around the top of the opening to even off the shaft. These supported by additional cut sod. As currently set, the furnace has a roughly oval interior, about 30 cm front to back and 35 cm side to side. Total shaft height is irregular at 55 - 60 cm. The tuyere is set about 15 cm above the dirt base (which could be dug lower). This creates a shaft height of 40 - 45 cm.

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Iron

Today I happened to sit through a class on iron by Kettil (Darrell Markewitz).

He talked about sources of iron, the basic processes to extract ore and turn it into iron, softer (easier to work), vs hard (holds an edge but brittle) and how both would be incorporated into things like knives or axes.

He also talked about the quality of iron produced and showed objects to demonstrate how it was used.

The most striking figure for me (Auðr) was the average amount of iron per person in a household: 2 kg. What that meant was you would have a personal knife but not much more. A ship needed around 2000 nails. Your household would likely have an axe, maybe some metal-edged farming implements, a cooking pot, and possibly  a bit more stuff like a cauldron hangar, pan or fork, depending on the size of the household. Things like fry pans and forks may have had wooden handles. A shovel would be wood with just a metal edge on the digging part.

Darrell has literally tons of experience making iron. 

2,500 kg of ore used

Just under 5,000 kg of charcoal

81 blooms totalling over 475 kg of iron

72 furnaces (some of which were reused for more than one smelt)

95 smelts

36 different kinds of ore

20 different kinds of furnaces to explore different styles and techniques based archeological remains

16 different kinds of air sources

He has a book coming out later this year to document his 25 years of historical iron smelting and what we expect to be over 100 smelts by the time of publication. Until then, you might be interested in one of his other books:

 

• Turf to Tools
  
• How Dense Are You?

Iron Smelt at L'Anse aux Meadows NHSC

This is a fast report on the bloomery iron smelt undertaken by a Parks Canada team, with some assistance from DARC, on Sunday July 16, 2017 - at L'Anse aux Meadows NHSC.
This was in conjunction with 'Historic Sites Day' - and in turn part of the ongoing Canada 150 events.

This is only the second time in the modern era that iron has been smelted at LAM, since Leif Eirikson and his crew undertook the process some time about 1000 AD.

This iron smelt was a very long one.

The 'smelt master' was Mark Pilgrim ('Little Ragnar'). He and I started at 7:00 am with the organization and pre-heat.
Main sequence start with ungraded charcoal at 10:45
(from here on constant bellows work by Ian / Kevin / 'Thorstien')
First ore (DD2 Analog) at 12:00
A bit of mix up there, poor communications / instruction (?) resulted
in the first charge being a full 2 kg , followed by a more normal 1 kg
amount.
Burn times ran an average of about 20 minutes each (fastest = 17 /
slowest = 29)
Total of 29 kg ore was charged, last addition at 5:36

Although the normal burn down to ready for extraction was finished at
6:45, the extraction was delayed to about 7:30 to allow the visiting
group from C-3 to assemble.
The end result of this was that the furnace interior had cooled, the
normally white hot bloom had shifted down to at best a bright orange.
This in turn resulted in great difficulty separating the bloom from
the slag bowl - and the slag bowl becoming completely frozen to the
furnace walls.
Mark undertook the extraction process, but in the end had to break the
furnace apart to free the mass.

Top of Bloom - showing 'scoop' from air blast.

The end result was a 5.5 kg bloom. Yield = 19 %

This is still a bit lacy on the outside, due to initial compaction
being undertaken well below the normal welding heat. Still the bloom
looks and feels quite solid under the hammer. This a marked contrast
to the crumbly texture of the 2010 results.

Cut (and broken) along the mid line. Top 'half' is to left.

Impressive work by all involved!

Iron Smelt Demonstration at ICMS - overview

Strictly speaking, the demonstration described here was not mounted as part of DARC. As Neil and I were both referring to DARC and handing out those business cards, I thought the event should be described here as well as via the Wareham Forge / Hammered Out Bits blog.


On Saturday May 12, I mounted an iron smelting demonstration at the 48th International Congress for Medieval Studies, at Western Michigan University, Kalamazoo MI.

The two day presentation was sponsored by AVISTA - The Association Villard de Honnecourt for the Interdisciplinary Study of Medieval Technology, Science and Art

The images bellow are scooped from the MiLive / Kalamazoo Gazette web site :


All images by Matt Gade
You can view an article by reporter Theresa Ghiloni, along with the sideshow of full sized images by following this link.

There was also some video shot of the extraction by fellow researcher Dr. Mike Cramer


My assistant and smelting partner Neil Peterson does figure dominate in the video and images above! Excellent work was done by conference members Keeney Swearer and Lisa Anne Conner for both the build and smelt days. 'David' helped on the build, 'George' was the second striker seen.

I would like to thank Steve Walton of AVISTA for organizing the demonstration.


For those curious:
Ore type : DD Analog, enriched with hammer scale
Ore total : 25 kg
Bloom weight : 5.4 kg

More images and detailed report in the works

Return to Iceland - IRON SMELT

Sorry for the extremely short notice here. (Life, the Universe, you know...)

Iron Smelt at Wareham
Saturday May 26
Return to Iceland

Directions - http://www.warehamforge.ca/directions
(that's roughly 2 1/2 hours NW of Toronto, 45 minutes N of Orangeville, just off highway 10)

In 2007, the DARC team had started working on developing a working system based on the archaeology by Kevin Smith at Hals in Iceland :
http://www.warehamforge.ca/ironsmelting/HALS/index.html
We got side tracked from the Hals / Icelandic series when we concentrated on the LAM / Vinland series, then preparing for CanIRON 8.
We had run four experiments in the Iceland series, testing use of stone slabs, general work arrangements, use of the bellows plate and blow hole system.

Theoretical Hals working layout

The next point in the series would be to construct another earth fast furnace, but this time with thin (3 cm) clay walls. It will use a ceramic insert tuyere, we have enough DD1 bog ore analog prepared for a smaller sized smelt.

I also want to use the smelting bellows for enough time to at least get 'in line' air volumes recorded. Bulk of the smelt will be with the electric blower (!)

I'm a bit pressed for time this week, but will attempt to get the furnace constructed over the next two days. There may be a bit more discussion before starting the pre-heat cycle than normal

Schedule:
8 A : start equipment set up
9 - 10 A : start pre-heat
11 A : estimated start for main sequence
11 - 11:30 A : bellows volume tests
12 N : estimated first ore addition
3:30 - 4 P : estimated start for extraction
4:30 - 5 P : estimated consolidation
5:30 P : pack down

For those new to Wareham:
1) Bring a lunch if you plan a day of it (its a 15 minute drive to the nearest town)
2) Park along the north side road (less traffic, they just laid fresh gravel here!)

There is always some dirty work to help with! Those wanting to get directly involved should dress for work, I will have extra safety glasses on hand.

Hope some of you will be able to make it up

Darrell

Measuring the HEAT...

Iron Smelting Furnace Temperatures
Short Shaft over Slag Pit

October 9, 2011 / DARC Smelt Team, Neil Peterson recording

On our last smelt, we set up to record furnace temperatures over the duration of the experiment.


The furnace was our standard short shaft type, roughly 25 cm interior diameter, 70 cm total height.
Walls were clay and straw cobb, about 10 cm thickness.
Fuel was hardwood charcoal (mainly oak) graded to .5 through 2.5 cm diameters.
Air volume via the tuyere (set at 20 cm above base) was roughly 800 litres per minute.

Holes were drilled through the furnace walls at roughly every 10 cm, starting at 10 cm above the interior base.
Measurements were taken using an industrial quality digital pyrometer (Model HH12B from Omega with type K bare wire thermocouples).
The probes were inserted roughly 5 cm beyond the interior surface of the furnace wall.
Measurements were taken roughly every hour over the course of the smelt event.

Because the probes did not reach into the central core of the furnace, there is every possibility that the central furnace temperatures were even higher than what was recorded.
Our thermocouples failed (melted!) at roughly 1350 C. On several recordings, this temperature was reached.

Image : Neil takes readings, early in the smelt

Time	Elapsed	base	tuyere	plus 10	plus 20	plus 30	plus 40	top
		10 cm	20 cm	30 cm	40 cm	50 cm	60 cm	70 cm
12:06	:06		653	890	749	579	343
13:05	1:05		1042	1335	1300	1145	1002	610
13:50	1:50	328	1051	plus 1350	1195	1189	1014	660
15:12	3:12	995	1226	1268	1293	1128	1011	608
16:32	4:32			1124	1265 *	909	700	719

Note: It has been suggested by some theoretical researchers that temperatures above 1200 C are impossible to achieve inside a charcoal fired furnace...

Cross posted from Hammered Out Bits

Thanksgiving Smelt - fast overview

'Celtic Iron Age' slag pit furnace

October 9, 2011
DARC smelt team
(Darrell / Neil / Marcus)

Showing the initial layout of the 'pit'. A standard 20 L plastic pail was surrounded by dirt, then filled to top with cut willow branches (about 0.5 - 1 cm diameter). Use of concrete blocks would allow for easy excavation after the experiment.


Our standard short shaft furnace is constructed on top of the pit. Clay with straw cobb, 25 cm ID, 70 cm tall. Ceramic tube tuyere (2.5 cm ID), electric blower.

Total time : 5 3/4 hours
Total charcoal : 57.5 kg
Total ore : 48 kg



Slag block as excavated (furnace itself was removed in one piece and retained for further use) There was no actual bloom recovered!


A fragment of the slag block, showing how hot slag had dripped down between the sticks, solidified, the heat converting the wood to charcoal. This from the front side of the furnace, indicating lack of iron (pale green colour). Slag to the rear of the furnace was a black iron rich colour.

The purity of the ore was questionable.
There is a chance some iron may exist trapped inside the slag block. A check with a magnet at the usual location (under the tuyere) did not indicate any however.
It is possible that the existing iron rich slag might be recovered, then utilized in a second smelt attempt.

For now we want to retain the slag block itself as a sample.


The extracted slag block. In this shot the tuyere is located to the upper right, directly above the scale vertical line. The colour shift in the slag from the rear to the front of the furnace is easily seen. There is an extra bulge in the slag about at ground level (the clay furnace sat directly on the loose dirt here.


A full report is in the works!
(duplicate from Hammered Out Bits)

CanIRON 8 Iron Smelt

This is a clip shot at the recent CanIRON 8 demo by Neil, Richard and Dave.

Neil Peterson describing ancient iron and the ore used in the demonstration.

The furnace used is our 'Econo Norse' test / teaching set up, the ore our DD1 analog.
The result was a good soft iron at 5 kg.

The full smelt report is under preparation by Neil.

This is a set of images by OABA's Sean Stoughton
Published in the Iron Trillium

Notice in all this, you don't actually see Ragnar doing any WORK!

DARC at CanIRON 8 - Preparation Smelt

- June 11 at Wareham
Smeltmaster - Neil Peterson
Lead Hand - Richard Schweitzer
Loader - Sam Falzone

Furnace - Econo Norse (standard set up)
Ore - untested rock ore from Bratton's Run, near Lexington Virginia
Amount - estimated at roughly 23 kg
Bloom - 2.65 nice soft iron

Slag tap 2/3 through sequence

Neil peeks while Richard loads

Compacted and sliced bloom

Full smelt report with images is now available on the main Wareham Forge Iron Smelting Documentation:
June 11 / 11 Report

Demonstration IRON SMELT : June 11

- The Dark Ages Re-creation Company will be mounting a demonstration IRON SMELT at the upcoming CanIRON 8 (Fergus, Thursday July 28)

http://www.ontarioblacksmiths.ca/CANIRON8/demonstrator/darc.html

The preparation / test smelt for this will take place on our normal
spring smelt weekend :

Saturday June 11
Wareham Ontario
Demonstration start time: 9 AM
Expected extraction time : 5 PM

Neil Peterson will be smelt master, demonstration team is Dave Cox, Sam Falezone and Richard Schweitzer.

Those interested in attending the June session can undertake the role of the general
public. This may mean that there may also be roles available as part of a
'hands on' aspect to the demonstration.

The smelter to be constructed is the Econo Norse type (firebrick with
sand packing). This is a modern system using easily available parts in its construction.
http://www.warehamforge.ca/ironsmelting/EconoNorse/index.html


In addition there will be some general grunt work to be undertaken, required to prepare materials for the two smelts. Smashing charcoal being one task. Breaking rock ore would be very
helpful.

Following the CanIRON pattern, this June 11 demonstration intended to be a ONE DAY
sequence.

How to get to Wareham?
http://www.warehamforge.ca/directions

Preparation for CanIRON 8 Demo (11-06-10 Smelt)

The DARC team, under Neil Peterson, will be conducting an open public demonstration of iron smelting as part of CanIRON 8, the Canadian National Blacksmiths Conference. In preparation for this demo, the next several smelts will be used to bring the working team up to full speed on our Econo Norse test bed furnace.

The first of these working production style smelts was held on Saturday November 6. Neil was the smelt master, Richard Schwietzer was the assistant. (I kept to the background and tried just to make suggestions and make notes on equipment.)

The smelt used 24 kg of ganular hematite, resulting in a very compact 8.5 kg bloom. This was spark tested and looks to be a high carbon metal.

A short photo essay on the building of the furnace is available on the main Wareham Forge iron smelting documentation.

Very nice work by Neil and Richard!