Monday, December 24, 2007

2007 Experimental Overviews Available

I have been plugging away over the last week taking the various raw data from the 2007 smelt season and getting it formated up for publication on the web site.

First - I have added the 'short form' overview to the series. The new 2007 information (with representative image) can be now seen at:

Second - Working ahead to the research that is planned for this winter, I have taken all our past data and put all the (currently) significant variables into one huge table. This is a bit of a pain to view because of the large number of elements listed for each smelt. It does relate details on furnace, ore, charcoal, process and results.

Neil is also currently in the process of re-designing the entire DARC web site, using a new layout that I think everyone will see as a great improvement.
(He has asked to hold the URL release until he has had time to work over the sub sections to the new graphic format.)

One thing you will see on comparing the two lists of experiments: In the past there had been some confusion over numbering. To the end of 2007, I make my own count at 28 smelts. I include in this all those that I felt I undertook a significant role. Just what 'significant' means is largely in the eye of the beholder. I have actually been at least marginally involved in a number of other smelts - those were I was more of an observer than active participant. This includes those where Lee and Skip were conducting the action.
I have always tried to distinguish clearly between the DARC series of smelts as being those where DARC resources in terms of manpower and raw materials have driven the experiment. For that reason I have not considered the 2005 OABA sponsored smelt at Wareham as part of the DARC series for example. This even though Neil was actually one of the team participating, with Ken Cook as lead charcoal monkey.
So my definitive list of smelt experiments lists DARC has undertook a total of 13 experimental smelts. Members of the group (Gus / Kevin / Dave / Darrell) also traveled to Virginia in 2002 to observe Skip and Lee at a public demonstration, but although we did participate with some grunt work on that smelt, it is not counted as part of the series.


Saturday, December 22, 2007

Expanded Smelt Data

I have been working over the data from past smelts - in an effort to see just where we stand to map out the 2008 experiment series.

Although the size of the resulting table is quite awkward, all the recorded variables have been posted up on my own iron smelting web site HERE.

This may prove only of interest to the real hard core iron smelting people. The table records furnace details, ore, charcoal, blooms and slag for all 29 (!) of the smelts I have undertaken to the end of 2007.


Wednesday, December 12, 2007

Easier than Smelting!

Uncovering the Secrets of Ireland's Ancient Breweries

Vandy had sent me a link earlier to a short piece on YU-Tube related to this same project. In short a large wooden trough set in the ground is filled with water and your ingreadients. Hot stones are added to bring the mix to a bowl. Pour into covered containers (barrels or large pots). Wait a couple of days.

Could not be easier...


(who is well known for the ceremonial Guinness AFTER a smelt!)

Saturday, December 08, 2007

Terrorism is NOT Art

I try not to get into too much political commentary here - but this one I could not let go by...

RIP: An obituary for shock art

Fake bomb didn't bring down the ROM, but it did mark the passing of an artistic era. Fact is, there's little left that can rouse us from our comfortable numbness

Christopher Hume
Urban Issues columnist

Thorarinn Ingi Jonsson's bomb wasn't real, but it might as well have been.

When the 24-year-old Ontario College of Art and Design student placed a fake explosive device – he called it a "sculpture" – inside the main entrance of the Royal Ontario Museum last week, he confirmed something that everyone outside the art world has known for awhile, namely that art has lost its power to shock.
So it's not at all surprising that Jonsson insists he'd do it all again; it was, after all, art. And he, don't forget, is an artist.

Yes, he admits he had no idea that his project would elicit a full-scale emergency response ... "

Hardly - This was terrorism.

Despite what the so called 'artist' thinks he may have been making as a statement, he remains a terrorist. Nothing more. Jail him as anyone else attempting to bomb - to terrorize - would be.

Forget a grand defense based on the history of art. Only a self absorbed fool would expect that planting something that looks like a bomb in a public setting would be seen as anything less than an extreme threat to public safety in our modern world.

I note the reviewer completely ignores the huge loss of both up front cash and hoped for charity donations that this 'art' inflicted on to the fund raising effort planned for the ROM that same day. I doubt any of those people see any value in this 'art'.

This is nothing more that the worst possible extension of the kind of garbage that has come out of OCA since before I was a student there in the 70's. It was crap then - and its even more pathetic crap now.

Thursday, December 06, 2007

'Gangue aux Fer' - on Early Iron

Expedition Magazine

University of Pennsylvania Museum

3260 South Street

Philadelphia, PA 19104-6324

Tel: (215) 898-4124

Fax: (215) 573-2497

Volume 49, Number 3

Winter 2007


Adventures in Experimental Smelting--Iron the Old-fashioned Way

Elizabeth G. Hamilton

Elizabeth is one of the consistent participants in the EARLY IRON series of symposiums. At Early Iron 3 (2006) she interviewed Lee, Skip, Mike and myself. This article is the result. The link will give you a direct download of the article as a PDF.

Thursday, November 29, 2007

Electric Blower for Iron Smelting

Although the DARC smelt team has been working towards a historical era smelt, AIR has remained a major stumbling block. Use of a straight Viking Age blacksmith's bellows clearly does not push enough air volume to produce the type of bloom found in the archaeology. Getting enough air via an electric blower is clearly not historical. This whole problem will one of the research projects for this winter (expect further posts as the work proceeds).
We have been making due with a circa 1960's vintage vacumn cleaner blower. This is tough, but frankly older than some of our team members! Although we now have a second such blower rigged, there have been tense moments in recent smelts when the primary blower has stopped for one reason or another. (As I myself am just slightly older than this piece of equipment - I feel its pain!) To that end, we are going to invest in a brand new industrial blower for the upcoming year.

I had the following recommendation by Skip Williams - Good Advice which I pass along to my readers...

We've been using blowers made by AMETEK. They come in two varieties
1) a multistage vane pump - super quiet - fixed air output
2) brushless DC moter - with variable output

We have both kinds. For Full Scale smelting we generally use the
fixed output variety with an air dump valve at the tuyere. For any
research with teeny-tiny furnaces it is nice to be able to turn the
fan down to just a few CFM... so I use the variable type. I've found
that the 63 CFM blowers produce much more air than I can use.

These blowers are available cheaply from online 'surplus' stores.
Just Google "Ametek Blower". BTW. the retail price is over $1000

Try this one:
50 CFM BLOWER AMETEK #116246-04.
Motor is rated 115 VAC 1.9 amps60Hz / 3450 rpm. Ball bearing. Continuous duty. Thermally protected. Five-stage centrifugal design. The blower will move 50 cfm
of air at 0" of water-static pressure. Vacuum rating is 10 cfm at 16" of
Circular inlet has a 1.675" I.D. and a 1-3/4" O.D.
The circular outlet has a 1.6" I.D. and a 1-3/4" O.D.
A rectangular mounting foot is located on the bottom of the circular fan body. The
foot is 3-3/4" wide x 2-1/2" deep. Four tapped mounting holes are located in the corners of the foot The holes are tapped 1/4"X20 tpi. The hole centers are 1-3/4" apart (front to rear)and are 3" apart side to side)
(includes starting capacitor).
Dimensions:9-3/4" wide x 9" deep (front to back) x 10" high.
RFE $119.00 Ea.

That list price is in US funds, and does not include shipping.

Tuesday, November 27, 2007

Martin Course Smelt

Martin Smelt Course - 11/25/07

This is a brief overview of the smelt undertaken as a course over the weekend of November 24 / 25, 2007 by Peter Martin and friends. Note that this report lacks certain details on the exact smelt sequence (others took the data there).

Saturday consisted of an overview lecture, construction of the smelter, plus preparation of the materials. One important difference with this smelt is that it took place INSIDE, on the main shop floor. The space is dirt floored with poured concrete walls and a 20 peak to the roof. This was done because of the start of winter weather (daytime temperatures just below freezing and with 4 inches of snow down).

SMELTER: standard Norse Short Shaft - clay cobb
Height: 72 - 75 cm
Diameter: 25 cm (internal)
Thickness : 6 - 8 cm (somewhat variable)
Tuyere: 2.5 cm ID, standard ceramic tube
Position: 22.5 down angle / about 4 cm proud inner wall
Base: about 10 cm below tuyere

The smelter was constructed on a low plinth, a line of standard bricks filled with tamped sand. The shape of the smelter was to our standard profile, controlled by using two sheet metal forms for inner and outer diameters. In this case the clay was mixed up somewhat on the wet side and was not compacted as evenly as normal (first time builders). The cob was made of commercial ball clay mixed about 50/50 by volume with chopped straw (no sand added). The structure was left overnight with the sheet metal forms in place to allow the clay to stabilize.

After the metal forms were removed, the structure was straightened and tap arch and tuyere cut into the walls. It was obvious that the soft clay was starting to slump, so a split hardwood fire was started inside. The internal base level was allowed to develop from ash and small charcoal remnants. A much longer than normal pre-heat sequence was undertaken to dry the clay - twice the normal at over two hours. Only the last 15 minutes was under the influence of the blower at its lowest setting.

The primary ore material was commercial taconite pellets, sourced from Defasco in Hamilton Ontario. These had been previously roasted in a gas forge and then water quenched (to ease breaking). The team crushed 36 lbs of this material to the normal 'rice to half pea' size. In keeping with some recent observations by Lee Sauder, a further 4 lbs of poor quality Virginia rock ore was set aside as a seed charge. The expectation here was that the higher silica content of this material would speed the formation of the slag bowl. In total 40 lbs of the two ores was used.

As usual, the main sequence started by filling the furnace with rough carcoal, followed up with additions of graded fuel (2.5 cm pieces). Air was set at roughly 750 litres per minute. This number is only an estimate, as the first blower failed part way through the smelt and had to be replaced with the standby unit. (There are no exact measurements for the second blower, but sound and consumption rates remained constant - suggesting close to the same volumes.) From the first, the smelter ran hot, with initial consumption of the standard 10 litre (about 4 lb) measure of charcoal in the range of 6 minutes. Significantly, the entire internal volume of the smelter very quickly ignited, shortening the time required to first ore addition.

About half way into the main smelt sequence

A fairly standard ore and charcoal sequence was followed. The material of the seed charges was added as 'slugs'. Time was allowed for this material to hit tuyere level before starting the main ore charges. A standard time internal was maintained at roughly 8 - 9 minutes per fixed charcoal bucket. As has been seen in the past, the furnace accepted ever larger volumes of ore inside those charcoal charges, in this case peaking at 5 scoops (about 2 kg) or about 1 : 1 ore to charcoal by weight. The alloted ore was added in roughly 3 hours. Latter in the sequence, the smelter make several self tapping leaks of slag. This proved to be transitional, thin and dark but with not enough iron content to be magnetic. As much as a teaching tool as anything else, this material was re-cycled. Over the course of the smelt there was no problem with too high slag levels. The tuyere only required rodgering out on two occasions.
Time was again given for the last of the ore to fall to tuyere level, then a last 'shock charge' of 3 scoops (about 1 kg) was added as a single slug. This was covered with a last two buckets of charcoal, then the furnace was allowed to start to burn down.

The furnace had been set up with a large enough tap arch to allow for a bottom extraction, but the team wanted to use a top extraction method. To that end, the interior level of burning charcoal was allowed to drop down to roughly 1/3 of the volume before extraction was started.
Air was cut back to a lower level (about enough to keep the interior temperatures constant) and the charcoal covering the slag bowl was scooped away. An attempt was made to loosen the bloom with the log 'thumper' but this proved less than normally effective. The tap arch block was pulled away, which also removed about 1/3 of the lower slag bowl which was stuck to the clay. The lower level of ash and some sand was raked out, making use of the thumper from the top more effective. With some use of a long chisel tipped rod it was possible to loosen and grab free the bloom with tongs.

The furnace had more fresh charcoal added and air blast returned. In this way it was possible to re-heat the bloom, allowing for several working heats to be taken. First, the loose mother was struck off using heavy hammers and an anvil set on the floor. Some attempt was made to compress the bloom in latter heats, but the smelter-as-forge set up proved not the best for getting back up to the higher heats required. In the end it was decided to use our remaining energies to section the bloom, a process that itself took three heating cycles to accomplish.

The bloom being re-heated after initial hammering

The finished bloom had a somewhat a lumpy and fragmented consistency. Spark tests after it cooled showed it has a range of carbon contents - from a good soft iron on one side through to a mid carbon on the opposite (guestimated at about .3 carbon) The total size of the finished bloom (before cutting) was 12 lbs. This is a 30% return on ore used.

In all a text book smelt, which proved perfect as a teaching experience for the team members. The furnace preformed perfectly, with no significant problems over the smelt. The sequence ran just as predicted, with end results almost exactly as expected.

Saturday, November 24, 2007

Winter Considerations

This last week I was invited to give a couple of lectures at Laurier University in Waterloo. Our smelt team has made friends with a couple of archaeology professors there - Dean Knight and Ron Ross.
The lecture of Dr Knight's ancient technologies course was on iron smelting (as might be suspected). At dinner, the lot of us got talking about the DARC experimental series, and what direction our future work might take.

Obviously one major thrust is the continuing series working towards a reconstruction of the Icelandic turf walled construction as excavated at Hals by Kevin Smith. This is primarily a furnace problem, and outside of the mechanics of gathering of the required grass sods, * seems * pretty straight forward. (The outlines of this project have been seen in earlier posts here.)

At this point, several deep background research projects are called for. These are mainly to take our practical experiences and frame them up against what is known from the archaeology:

1) Overview of Blooms and Smelters
Right now our best single resource for historic prototypes is Pliener's 'Iron in Archaeology'. Unfortunately most of the information we really need is buried in hard to find and harder to access field reports and journal articles. What is needed is a simple table style listing of the data from individual finds. Location / measurements / dates. Especially a cross linking of smelters against blooms and source ores.

2) Overview of Experimental Smelts
There is no standard set of records being kept by individual smelt teams. The arrangement of furnaces / air systems / ore against bloom production is often hard to pin down. Not everyone keeps measurements on things like air volumes. Again what would be extremely helpful would be a simple table style listing of the related data.

3) Air Systems
Our own team has developed certain impressions about what form historic air systems may have taken. A formal consideration of the theoretical footprint of the various alternatives should be written. At this point we should be able to estimate (if not clearly illustrate) the impact of the various possible systems in terms of things like debris fields.

Each one of these represents at least a potential journal article, if not a full blown academic paper (maybe a thesis!). A number of our close correspondents and advisors have been suggesting that we should be working to publish some of our experiences and conclusions.

Something to keep me inside next to the wood stove come January and February...

Wednesday, November 21, 2007

Extending Asumptions

(Blended from a couple of posts to NORSEFOLK)

"...Note the Throndjem woman's bead necklace. She (a re-enactor) told me that the necklaces were rarely symmetrical. Each bead 'told its own story' as to where and when it was collected or bought or traded...."

(name deliberately removed to protect the inocent)

Not a remote chance that this statement can be any more than a single person's imagination. In some cases it may be possible to tell from location in an excavation the order of the beads, but in most cases these have so widely scattered as the body settles that the original order can only be guessed at. If your sources are museum presentations - often the order has been 'reconstructed' at the taste of the conservator.
As to why a specific bead has gone where - it is absolutely impossible to attribute order to some cultural activity.

Note that I'm not discussing the details of bead necklace construction, save as an example of a larger concept in interpreting objects. (Karen mentioned this, as she and Neil and Meghan and I have much hashed over the topic of beads and interpretations frequently).
There are a number of different ways a person could assemble the order of beads on to a string:
One most important variable would be the method of collecting the number. Purchased all at once - or collected over time (and perhaps space)?
Was the order static - or was it constantly being modified in terms of order and additions?
Is the combination in any way symmetrical? If so - what is the measure of balance? This is particularly important, because if you look at the use of semi-precious stones set on metal objects from the same time, you will see that 'balance' may be in terms of matching size / matching shape / and not as often matching colour / matching material.

Now there is absolutely no way that we can measure if bead order was determined by some sequence of applied memories in the mind of the owner. I suspect that this assertion was made on the basis of negative evidence - 'we see no other obvious order, so therefore the sequence is based on memories'. Could just as easily be totally random . Could be based on purchase order. Could be 'the strand broke and I was in too much of a rush to just get all the beads stuck on a strand again to bother'. Any of these others just as likely.

(Sandy, a researcher at the Frojel site in Gotland Sweden commented on some finds there.)

Sandy's description of the half blue / half silver strand illustrates an important point. (Going out on a pretty thin limb here) - It is most commonly seen that the order chosen by the Norse was much different than the order chosen by Victorian archaeologists - or that chosen by modern taste. I'm not attempting to get into the details of individual strands, as I have certainly NOT studied these in enough detail to present specific examples.

I comment on the underlaying concept - Take care applying modern opinions to historic details.

Tuesday, November 13, 2007

Beowulf / Shamol-wulf

I thought some of you would get a laugh out of this. The text found and forwarded to me by my wife Vandy. Remember those descriptions of pieces I had done for the long lost 'Outlander' film? Well everyone jumped on the bandwagon of our Anglo-Saxon Hero a while back. The lastest version is just hitting the theatres - and the * trailer * even looks like a bad video game...

From Antagony and Ecstasy, one of the movie review sites Vandy reads:

A cartoon is coming, || computer-created,
Generated on green-screen , || the graphics laid over.
Beowulf is the book || bound for the movies,
Retold by that rascal || Robert Zemeckis,
His camera is clumsy || compulsively gaudy.
The trailer is terrifying || a tragic misfire
Of video unviewable || and a valley uncanny,
The proud performers || plastic and ugly

Wednesday, November 07, 2007

Riverdale House - 2nd Install

On Tuesday (Nov 6) I installed the next two units of the Riverdale House railing project in Toronto

The third piece of the project was a half circle railing, 48 inches in diameter. To make both my fabrication, but more importantly transportation, easier, this was made in two pieces. A central leg was required to support the centre of the panel, so it proved fairly simple to run three bolts to joint the sections. This approach also allowed for a slight bit of flex to the curve during installation. Despite my butter fingers (after a three hour drive into Toronto) this unit fit its space exactly and proved quite quick and easy to secure into place. On subtle feature of this panel was that the leg piece had been hot punched with the names of the client and the date.

The fourth piece installed was the right hand (seen from the street) stair hand rail. This is the straight section. This proved a wee bit more of a problem to fit. Of course none of the angles on the wooden stairs proved to be at 90 degrees to each other - which can prove a series problem on a 9 foot long diagonal. In the end the railing fit fairly well. I had come prepared with some wooden shims (just in case). By lifting the lower support at the top deck level about a half inch, the rest of the support pieces fit pretty close. It proved possible to screw down the various attachment points tight to the existing stairs. I was quite pleased with how solid the finished hand rail was when fully attached with the lag screws.

This is a final view of the elements installed so far as they appear from the sidewalk. One panel remains - the curved hand rail for the left side stairs.

Further details can be seen on the main Wareham Forge web site :

Thursday, November 01, 2007

Icelandic Smelt Two (report)

Stone Slab with Low Air

As was mentioned earlier, the DARC fall smelt was originally intended to follow on the development of an Icelandic style smelter.

Front Elevation Drawing

On Friday, Darrell, Neil Peterson and Ken Cook worked on preparing the site and building the furnace. After a fairly wide ranging discussion, it was decided to work towards two experimental objectives:
1) Running a smelt with lower volumes of air.
2) Build the furnace using a stone slab construction method.

The all stone slab construction was an extension of the Thanksgiving smelt, which had just the front section of the smelter made of stone. It also was a return to our very first group smelt (in spring 2002). The material on hand were relatively thin and randomly shaped pieces of mica schist. Despite some concerns about how water can create some potentially explosive effects on this stone when it is subjected to high temperatures, the material once again stood up extremely well.

Ken at work sealing gaps with clay

The shape and proportions of the furnace was largely the result of the irregular shapes we had on hand. The overall height of the structure was also limited by the amount of stone available. Ken undertook most of the construction work, fitting the various slabs together as best he could. Considerable attention was focussed on the lower section and the front above tuyere level. The gaps between the slabs was filled with prepared clay cobb and sealed using wet waste clay. Once again the advantages of the straw fill in the cobb was obvious over the course of the smelt. The finished smelter actually most closely resembles the construction suggested for L'Anse aux Meadows.

Furnace with tuyere in place - pre-heat phase

The finished furnace was deemed to be the ugliest one we had ever constructed! A large tap arch was blocked out by a nicely shaped stone. It was decided to use a bottom extraction method for this smelt. This resulted in a rather large lower section to the furnace, so a base level of charcoal fines was established. With the height of the tuyere elevated above ground level, but the total height of the furnace about the standard, the effective shaft height above the tuyere was reduced.
Another wrinkle on the construction was a ledge of stone from the piece used to span over the tap arch. The tuyere was positioned so that it came just to the inner lip of this stone. In effect this placed the tip of the tuyere about 6 - 7 in from the line of the smelter interior wall.

Chamber size at Tuyere : 25 cm (front to back) x 35 cm (side to side)
Total furnace Height : 70 cm (random)
Shaft Height above Tuyere : 40 cm (minimum)
Height of Tuyere above base : 18 cm
Tuyere angle : starts at 26 down, latter shifted to 10 down
Tuyere size : standard 2.6 cm ID steel pipe

It was expected that the lower air volumes would greatly extend the time required for the smelt. Although better intentions were made, the pre-heat was started at our normal 9 AM, with primary smelt sequence started a bit after 10 AM. As normal, pre-heat was using wood splints, passive at the start and for the last 15 minutes or so using gentle air.

For this smelt, Neil was the iron master, with Ken working as lead hand. Darrell started the recording, with Ron Ross managing the latter half of this task.

It was decided to seed the smelt using the poorer quality Virginia Rock ore gathered last year by Darrel and Vandy. Although this material has proved to have too low an iron content, it was hoped that it would compensate for the lack of slag seen with earlier uses of the hematite grit. It was also expected that considerably less slag would be available inside this smelt with the use of stone instead of clay for the wall materials. In the end it proved we were overly conservative, and production of a suitable volume of slag would prove a problem.

With the lower consumption rates expected as a result of the lower air volume, it was also decided to limit the total amount of ore added. It was expected that this would only allow for the formation of a small bloom. The air volume used over this smelt was about 400 litres per minute - compared to the usual rate employed in past successful smelts at closer to 800 plus LPM. As was expected, the lower air greatly extended the time between additions of the standard 10 litre charcoal measure, which increased from a normal 8 minute average to closer to 22 minutes. The construction of the furnace had reduced the height of the reaction column from our normal 55 - 60 cm to closer to 40 cm. Still the theoretical 'drop time' for any individual particle of ore had been extended from a normal 25 - 30 minutes to double that - closer to 60 - 70 minutes. This was expected to produce problems in carbon control with the fine particles of the hematite grit.

At the start of the burn down phase - note heat effects around tuyere

A secondary concern was the amount of penetration of air into the body of the smelter, again an expected effect of the lower volumes. Several times during the smelt, the depth of the heated zone was measured at tuyere level, This was done by the simple process of inserting a 3/8 diameter mild steel rod held horizontal to the ground through the blow hole. After about two minutes the rod was pulled out, and the colour of the rod used as a simple measure of heat. The rear 1/3 to 1/4 of the rod did not show any visible colour, indicating that the area of the furnace furthest from the tuyere had to be below 600 C. It was hoped that additions of ore would none the less drift towards the ignition area above the tuyere regardless.

Over the course of the smelt, the following totals were recorded:

Ore : 12.3 KG (10 kg hematite grit / 2.3 Virginia rock)
Charcoal : 170 litres + 6 kg ungraded fuel at start
Time : Main sequence = 6 hours

Generally the slower consumption rate lead to a much less frantic smelt sequence. It was obvious fairly early on that less slag was being produced. Although the furnace had been constructed as an 'incontinent' type, little slag was ever observed flowing from the slag bowl (even after the tap arch was opened latter in the smelt).

Neil reaches in with the bloom tongs, the bottom of the slag mass can be seen

Neil undertook the extraction, and was able to grab almost the entire slag mass as one piece. There was little liquid present, and not much remained inside the furnace (generally both bad signs). Kevin Jarbeau and Ken worked the surface quite lightly with the hammers. Almost immeadiately, the majority of the mass split away, obviously only slag. The material remaining was extremely granular and poorly sintered. Even under gentle strokes of the large hammers, it quickly broke into a number of golf ball size pieces. Although we had hoped for a least a small well consolidated bloom, it was clear our product was too fragile to work.

The next day the cold smelter was excavated, with a good photographic record made and representative samples collected. All the slag was collected, and the area was cleaned with the large magnet. The results of this work:

Weight of Slag : 3.5 KG
Weight of Reduced Ore (but poorly or not sintered) : 3 KG
Weight of 'Bloom' (fragments) : 2 KG

Fragments of still hot 'bloom' in place on the stump

Although the general opinion on the day was that the product of the smelt was in fact a high carbon cast iron, I personally had some doubts. In past uses of the hematite grit as an ore material, the results even with high air volumes always had a granular texture and a high carbon content. On Tuesday I attempted to work one of the denser fragments inside the coal forge. Knowing how fragile this granular material would be, the roughly goose egg piece was brought close to a welding heat and very gently worked with a wooden mallet. Even under the lightest of strokes it was not possible to do much more than just push the grains a bit closer together. I was not able to actually forge the material into any kind of solid piece. The end result was just a larger pile of smaller fragments. One piece (about 3 cm wide and about .5 thick) was compressed enough to have a noticeably flat surface, this was taken to the grinder for a spark test. The sparks produced were like those seen from a piece of high carbon tool steel (in the range of 1 % plus carbon content). It may prove possible to forge weld the fragments between two other slabs, but I was unable to work the material as it exists at this point.


1) The construction method using stone slabs with clay cobb sealing the joints is certainly viable. It is unlikely that the mica schist material would withstand a second firing without heavy replacement of the material at the normal hot zone above the tuyere. The stone in this area exhibits both considerable erosion and also a thick deposit of slag. Both of these effects should remain clearly visible in archaeological remains of this type.

2) The use of lower volume air requires considerable further experimentation to develop a truly successful sequence. As has been clearly demonstrated with both our earlier smelts and those of other experimenters - there is a (poorly understood) relationship between ore type and purity, smelter material and design, fuel preparation, and physical sequence. Those attempting smelts with low air volumes have great difficulty (if able at all) in producing large and well consolidated blooms.

3) In retrospect, it is most likely that both the content and the fine particle size of the hematite grit renders it quite unsuitable for use in any kind of low slag producing smelter. The extremely low silica content of the ore means that the formation of slag must come almost exclusively from the melting of the smelter walls. Although good results have been attained with this material in past smelts, this has always been inside those furnaces that have suffered considerable internal erosion.

Recording Smelting Slags

In the recent set of conversations backgrounding the Icelandic smelter series, Kevin Smith had asked me if we had been keeping any records of the amount of slag produced in each experiment. Truth is that although we have numbers for ore and bloom, we generally have no records for the amount of actual slag created. This is certainly a significant measurement, as there are very few metal blooms found - these were just too valuable considering the effort that had gone into creating them. Slag, on the other hand, is nothing more than a waste product, and an extremely durable one at that. There are literally tons of various slags, even within a single major historic iron producing site. Hals in Iceland, for example, Smith estimates there is some 5000 kg of waste slag. *

Slag remains are also used by modern researchers to estimate the probable yields of individual ancient smelts:
- First the ore utilized will be examined. Normally it is expected that there will be some 'slop' of ore to be found right close to the shaft of the furnace. (In our own work, we always end up dropping some ore material by accident as it is added to the top of the furnace.) By analyzing the relative iron content of that ore, an idea of the starting ratio of iron and other waste products (which will go to the slag) can be gathered. As has been pointed out by other contributers to the Early Iron discussion, there can be a couple of reasons why the ore materials found around a smelting area could be misleading. Ideally an experienced worker can make a good judgment of the suitability of an individual piece of ore at the gathering location. In many cases however, our own experience has shown that it is only after ore is roasted and broken for size that good quality may become apparent. Much of the ore found around a smelter site may actually represent this discarded material. Little (if any) of the actual ore utilized for the smelt itself may remain.
- Next the slag itself is analyzed for the remaining iron content. This can only supply the roughest of estimates for a number of reasons. The slag found will certainly vary considerably. The quality of the slag will change over the course of a smelt, from the viscous bubbly iron poor slag at the first stages, eventually becoming a thin hard iron rich material in the latter stages. Slag from any given point in the several hour process of the smelt can be quite different in composition. Even inside a large slag block from a single smelt event, there is certainly differences in iron content remaining at various points within the mass.
- Not only the ratio of iron and silica from the ore effect both volume and nature of the slag, but the materials and set up of the furnace itself have a major effect. Different wall materials will erode at quite different rates, and of course melted furnace walls are a major component of slag. Generally only the very base levels of a furnace will remain to be examined. so at best the amount of
- The mechanics of a single smelt will greatly effect the way slag may be scattered over a working area. In most cases these processes will change the visual appearance of the slag materials. Tap slag will have distinctive flow patterns for example. As hot slag is always a problem to the operators, discarded slags may be tossed some distance away from the working area. Our own experience has shown that a large amount of material may be pulled away from the slag bowl inside the smelter when the bloom is extracted, especially if a bottom extraction method is used. This material usually has a certain amount of partially sintered ore with it. (What Sauder & Williams call 'mother'.) This loose material is going to be found not at the smelter, but at the area where the initial consolidation of the hot bloom is to be carried out. This location is certain to be close by to the smelter, but may in fact be removed by a number of metres (and thus may not be uncovered by the excavation at all)

In our own experiments, we have generally been working with ores that run in the range of 60 - 70 % iron content. Our yields vary considerably, but run from about 30 - 40 % metallic bloom against ore.

For the last two smelts, we have attempted to recover as much of the slag produced as possible. This can hardly be considered a representative sample, more (and more detailed) observations need to be made.

EVENT Icelandic ONE Icelandic TWO
DATE 10/8/07 10/27/07
SMELTER Norse short shaft Norse short shaft
CONSTRUCTION clay slab / stone plate stone slab
NOTE start low, high majority low air volumes
ORE TYPE hematite hematite
WEIGHT  12.3 12.3
BLOOM 6 5 (see note)
TYPE dense lens badly sintered
SLAG  8.5 3.5
TYPE complete bowl broken pieces
TAPPING none incontinent
OTHER no mother measured all included

Note : On Icelandic TWO, the 5 kg listed includes all materials recovered
- 1.7 kg small un-sintered fragments
- 2.3 kg badly sintered pieces (larger than 6 mm)
- 1 kg roughly golf ball sized denser pieces (considered true bloom)
Overall the material produced from this smelt proved too fragmented to forge, with an extremely high carbon content.

* With my recent focus on Hals in Iceland, I would be remiss if I did not provide readers with the reference for further details:
'Ore, Fire, Hammer, Sickle: Iron Production in Viking Age and Early Medieval Iceland'
Kevin Smith
Kevin has become a good friend and a close advisor to our experimental work over the years. He has contributed considerable depth to my understanding of the archaeology of iron smelting through our ongoing personal communications.

Tuesday, October 30, 2007

Bellows Test

Revised Air Delivery Test - Norse double chamber bellows
Darrell Markewitz & Neil Peterson, raw data by Peter Martin

A series of tests were made by Neil Peterson and Peter Martin at the DARC smelt in Wareham on October 28.

The bellows used is a reconstruction of a Viking Age blacksmith's double chamber bellows. The reconstruction is based on the two existing images of this type. The side depiction from Hylestad, Norway with a human figure provides relative scale, the top view from Ramsund, Sweden gives us proportions of length to width and valve size.

The rough dimensions of the reconstruction are:
total length: 70 cm (28 inches)
total width: 20 cm (20 inches)
individual bag length: 50 cm (20 inches)
individual bag width: 25 cm (10 inches)
effective loft height: 30 cm (12 inches)
inlet valve size; 10 cm (4 inches)
outlet tube size: 2 cm
For a fuller discussion of the reconstruction- go to an earlier BLOG Post

The tests were undertaken by a number of operators. The skill levels ranged considerably, from trained blacksmiths through to those who had never used any kind of bellows before. This was done to give the largest sample over the largest spread of skills. (It can be assumed that after several hours of working the bellows during a smelt, skill levels would come to be quite good - and air volumes more consistent.)
It should also be noted that the Y tube running from the bellows was tied in place, but not sealed with clay. This would have allowed some seepage of air before it could be measured at the exhaust end of the bellows tube.

Measurements were made by Peter using a small hand held anemometer which would record an average flow over a time period of 20 seconds. Number of strokes delivered over the time were counted. This allowed individuals to develop a consistent pattern of strokes before the measurements were taken. The first control level was taken with the anemometer held over the exhaust tube of the bellows.

An attempt was made to estimate the effects of resistance such as that would be created inside a working smelter. Neil made up a simple filter was made by layering 'landscape fabric' into a wooden frame which could be placed over the bellows tube. Measurements were made while each operator pumped against one, two and then three layers of this cloth. (Note that there was no attempt to actually match these filters against the real resistance of a working smelter.)

L/min figures below assume a pipe with 2 cm interior diameter (18.8 is the resulting multiplier)



m/s - no pressure test (L/min)

m/s - pressure test 1 (L/min)

m/s - pressure test 2 (L/min)

m/s - pressure test 3 (L/min)



11.1 (209)

7.1 (133)

6.9 (130)

5.1 (103)



13.6 (256)

7.3 (137)

7.1 (133)

4.9 (92)



11.7 (220)

7.1 (133)

7.1 (133)

4.3 (81)



9.3 (175)

6.3 (118)

5.5 (103)

3.2 (60)



11.2 (211)

8.4 (158)

7.5 (141)

5.4 (102)



10.0 (188)

8.0 (150)

6.7 (126)

5.2 (98)



11.15 (209)

7.4 (139)

6.8 (128)

4.7 (88)

Observer's comments:

" As bag pressure increases stroke length shortens and stroke rate increases proportionately. Operator notes increased bag pressures and "maintains" "constant" pressure at bottom of stroke resulting in arithmetic decrease in flow rate at logarithmic increases in air resistance. " (Peter)

" Way too many math terms that I'm not sure truly apply - I'm very leary of the word usage here although I agree with the jist of the observation, pump rate goes up, stroke shortens and flow rate decreases. " (Neil)

With that said the pressure tester adds a theoretical geometric (or exponential) progression of resistance (0,1,2,4). (Theoretical as it may be that putting in two layers makes it 4 times as hard to move air, or only 1.5 times as hard as one layer.)

The drop off on flow isn't even close to that sort of progression. The drops are 33%, 8%, 31%. It is interesting that any resistance at all produces a very significant drop, doubling? that resistance then produces only a minor fall off, but doubling? again produces another hefty drop off. Perhaps we are approaching the limit of the bellows to move the air.

It was noted (Peter) that a more useful measure of resistance would have been produced by use of a graduated tube full of charcoal particles.
Creating some method to introduce an anemometer 'in line' during a working smelt would also produce valuable information. (In the past all air volume measurements have been recorded with the blower venting with no resistance.)

In earlier writings, estimated values for the air delivered by this system were calculated by measuring the output of an earlier version of these bellows. This was done quite primitively, by means of attaching the bellows tube to a large garbage bag. Ten standard strokes were then made. The resulting bag of air was then placed inside a container of known volume, and the level compared to the total size of that container. This then produced an average volume produced per stroke at 2.2 litres.
Working stroke rates were determined from actual operation of that same bellows by various (untrained) operators during the Early Iron 1 experimental smelt It was observed that the average strokes per minute over a working period of 10 minutes was roughly 1 per second.
Taken together, these numbers produced an estimate of working air delivery set at 120 litres per minute.

In light of the better estimates produced in the test reported above, it is obvious those earlier volumes are incorrect. In effect however, at a working smelter producing considerable resistance to air flow, the original estimates still are close enough to the results of this test series. The earlier conclusions about the effective delivery of the Norse double bag bellows - in a size indicated as blacksmith's equipment, remain supported.

Friday, October 26, 2007

Historic Blooms?

Some thoughts on Blooms

I have been spending more time than normal in discussions related to the current series of experimental iron smelts. These include members of our working team, iron masters Lee Sauder & Skip Williams, and researchers Kevin Smith, Arne Espelund and Birgitta Wallace. (In various combinations, with separate topic threads intertwining).

I wanted to pull together a couple of things for the interest of my readers (and fellow pyromaniacs). Please remember that the following represents ideas from any (sometimes all) of the people mentioned above, who may not be clearly represented. With that large grain of salt taken - read on...

A reasonable question was raised about how I keep comparing the blooms we have been making compare to actual Viking Age artifact blooms.

First a note on our sizes:

I had decided to keep the sizes of our blooms into the small end of those found from the Viking Age. As was pointed out to me by a couple of people, historic blooms tend to range closer to 8 kg on average, with a few samples as much as double that weight. From what we have learned from Lee and Skip, and our own direct experience, once you get the iron bloom ball rolling, its actually pretty easy to just keep packing on the size. Inside the reaction, the furnace reaches a point where to maintain a consistent burn rate (at roughly 6 - 10 minutes for 10 litres) you effectivley dampen down the heat by adding ever larger charges of ore. In some smelts we have seen ore additions raised to as much as one and half times (by weight) of the charcoal amounts, inside a consistent consumption. When that happens the end product are truly monster blooms - in the range of 20 kg (Lee and Skip have gotten even larger ones).
In truth, there is a basic amount of fuel expended to get the interior of the smelter at the conditions for the creation of any bloom in the first place. This will vary by the construction and size of the smelter, does tend to represent 50% or better of the total fuel consumption. It makes practical sense to just keep piling on the iron once you have gone to all the work to get things happening in the first place.

The counter to this is : How do you work that huge lump of metal afterwards? For those other modern blacksmiths reading, imagine hand forging a piece of iron which is an irregular half ball shape, roughly 10 cm thick by 20 wide. The obvious solution is - POWER HAMMER. But what if you did not have any? Even trying to re-heat such a large mass after it has cooled is a daunting task...

We also have been influenced by our initial starting point in all of this - the Viking Age iron smelt at Vinland by members of Leif Ericsson's crew circa 1000 AD. The written reports suggest roughly 3 kg of iron were produced at that first smelt in North America. (Although its important to note that I'm not sure if that number may refer to the estimate of the workable iron produced, not necessarily a measure of the weight of the bloom out of the furnace.)

Taken altogether, the DARC series of smelts have kept the size of the blooms produced in the range of 3 - 5 kg. I certainly feel that if we can make 3 kg of good workable iron, we could have easily produced 10 kg with just a bit more smelt sequence. It also leaves us with a mass of material which is much easier to manipulate into the consolidation phase of the process.

Second - physical appearance:

Kevin Smith commented "...those who wrote about these Norse bloomery furnace blooms were convinced that the archaeological examples in question were blooms that had been consolidated to that shape and density through initial forging/welding, perhaps in several steps, after removal from the furnace."

Kevin is exactly correct that many of the artifact blooms show a distinctive 'hockey puck' shape, a flat sided disk, often sliced from one edge into a 'pac man' profile. As he states, this specific shape is clearly the result of heavy compaction hammering of the bloom. There are also however a number of samples which have a clear convex / concave bottom and top shape to them. These are almost identical to what we are pulling out of the furnace from our own smelts.

Iron Bloom - Oyane, Telemark, Norway (19.5 cm dia.)

'Resurrection' Bloom - Wareham, 10/2006 (18 cm dia.)
bottom uppermost

On extraction, the bloom mass will have a dished bottom surface, with the upper side either flat or slightly dished in. The top surface is normally well compacted, the lower side somewhat less so, with the lightest structure to the circular edges (especially the side furthest from the tuyere).
We often end up doing not much more than a very quick surface compaction on the still hot bloom after it is extracted. With a good quality dense bloom, the core is noticeably very hard, with lacy material attached to the edges. The first working over with hand sledges will either compress in, or often just knock away this attached material.

(more to come)

Sunday, October 21, 2007

GRAVE GOODS - Call for Entry

A Juried Exhibit of Contemporary Artisans
Woodstock Museum - Woodstock Ontario
September 5 to November 1 - 2008

In Ancient times, providing for the needs of the dead into the after life often exhibited the best work of artist and craftsman. Much of what we know about these lost cultures comes from clues found in graves. Into the early years of Canada's history, people continued their own distinctive and often elaborate traditions around burials and morning. How future ages may view our current era is sure to be coloured partially by what objects we use to mark our own passing.

Be it whimsical or serious, conceptual or traditional - GRAVE GOODS seeks to explore how the current generation of artisans view all aspects of burial customs. Original objects in all mediums created after September 1, 2007 are eligible for entry. Artists are being juried based on past works to encourage the creation of new pieces specifically for this exhibit. Grave Goods further explores the themes set out in the Woodstock Museum's special program for 2008 - 'Funeral Rites'.

Exhibit Guest Curator : Darrell Markewitz (Reflections of the Conquest, Out of the Fiery Furnace)

Special Exhibit Host : An Droichead / the Bridge

Key Dates:

Jury Entries - Start : November 1, 2007
End : June 1, 2008

Documentation - Due : July 1, 2008

Object Delivery - At the Woodstock Museum no latter than September 3, 2008

Check the web site:

Please! Feel free to pass along this open call information to any other artists you know who might be interested.

Friday, October 19, 2007

Possible FOOT powered air system

If you have been following the discussion of historic iron smelting, you have seen that the problem of air volumes has been an ongoing problem. Simply put, the method developed by Sauder & Williams, which works almost every time, requires the use of high volumes of air. Their theoretical model (and practical experience) calls for 1.2 to 1.5 litres per minute of air per square centimeter of smelter interior at tuyere level. In our case with the 25 - 30 cm diameters, thats in the range of 800 litres per minute.
Our problem is that working with the * reconstructed *, * blacksmith * bellows based on * only two * * period illustrations * with * no artifact evidence * - the best we can produce is on the order of 120 litres per minute. (Note all the potential errors!)

So I had sent a direct question off to a number of experimenters and researchers about bellows sizes and types for Dark Ages Europe.

Both Arne Espelund and (quoted) Skip Williams reminded me :

"... Actually, if you take a close look at the 'log framed' furnaces in Evenstad, at Trondelag, etc. you will see that there is a thin wall where the tuyere in inserted and sort of a large access arch over the bellows. This is probably the closest parallel we have to an Icelandic bloomery; same culture; different time and place...."

I also was sent this reference by Peter Hurley :

"...I think the following link may be helpful. It contains a conjectural reconstruction of how a foot powered two bag bellows might have worked. It remains only to build one and test it's potential output. For 800 litres of air per minute, I estimate each bag would have to have at least 8.7 litres of capacity assuming a pace of around 46 "steps" per minute:..."

That reference is from a book 'A Smaller Social History of Ancient Ireland' by P.W. Joyce - 1906. This appears mainly to derive its information from various written documents. The commentary discusses blacksmithing equipment and does not clearly give any date information (or artifact sources). It does describe yet another set up for foot powered bellows (though not as elegant a mechanical system as the Evenstad ones.)

Skips reference to the Evenstad process and set up is interesting (and admittedly something that did not come to mind). This is a larger scale multiple use smelter intended for top extractions and repeated hot swap firings. The largest problem I can see with the layout is that there is no provision for slag tapping. The tuyere also looks to be set too close to the base of the furnace for development of the slag bowl and bloom either.

The more interesting note is the 'traditional' bellows construction. Double chamber, but foot powered. At Hals there would have to be some kind of frame in place to make this set up work. I did a real fast ball park estimate from the measurements from the Evenstad document (from Arne Espelund's 'Iron Production in Norway') and get a (very rough estimate!) of 140 litres per stroke (empty one bag). Our own experience with the large UbberBellows had shown that the speed of stroke is limited by the time it takes to push the air through that 2.5 cm ID tuyere opening. ( That hand powered reconstruction is about the same volume - but slightly different proportions.) Our constant average was about 6 strokes per minute, with 10 stokes possible at least on short bursts. That suggests a delivered volume from 840 to maybe 1400 litres a minute.
If I'm reading the source document correctly (the translation and style is sometimes not clear) the mouth of the Evenstad tuyere is 3" diameter - which would make for easier delivery through the pipe. This in turn would make it possible to increase the pumping rate (thus delivered volume) above those numbers. Now I have an eliptical trainer trainer workout machine here, and even in my pathetic condition can easily maintain 30 plus strokes per second against some resistance. So being REALLY theoretical, lets peg the top end from the Evenstad set up at as much as 3200 litres per minute.
The Evenstad furnace is roughly 60 cm internal diameter (according to Espelund's conversion of 1 ell = 60 cm). That gives us a surface area of roughly 2700 cm. Using the Sauder and Williams calculation for effective air delivery, that suggest an optumal volume of at least 3250 litres per minute. Bingo!

Tuesday, October 16, 2007

Thanksgiving Smelt - some considerations

Neil and I have been looking at our measurement system with a bit of a critical eye:

First off - there have been inconsistencies in some of our past experimental data. This has most often come from not making correct account of the variation in the unit weights of some of our raw materials.

Charcoal varies a lot in terms of its density, this primarily due to the amount of water that may be incorporated in various sources and individual batches. The material from Black Diamond Charcoal for example is particularly dry. The primary adjustment here is recording totals as volume - rather than as raw weight as has been done in the past. During an actual smelt, we are measuring by a standard bucket volume anyway (then calculating the weights.)
The measured volume of our standard bucket is 10 litres.

Ore is also measured by a standard scoop, again working in volume. The calculations from number of scoops to weight has proved to contribute the largest error in the past. The problem here is the widely differing densities of the various ore types that have been used. The Virginia Rock ore for example has an average weight of 12 ounces per scoop, with the hematite grit closer to 20 ounces for the same volume.
The best suggestion here is to measure the weight of a standard scoop of ore for each individual smelt event.
The weight of a scoop of the hematite grit is 560 gms.

Air is delivered by an electric blower controlled by a marked switch. It is also becoming obvious that the normal vacumn blower is starting to show its heavy use. (Although a rugged piece of equipment, it is several decades old!) The light dimmer switch being used as a volume control is also likely to degrade with time. This became appearent during the last smelt, when the dial mark that used to show the 'just kicking over' position was in fact producing not enough current to start the blower running.
The best suggestion here is to measure the various marked volumes with the anemometer for every experiment.
The just measured air volumes are posted HERE

The relationship between air volume, charcoal consumption, reactive column height, and ore particle size needs to be re-considered for the next experiment in the Icelandic series. Up till now we have been following Sauder & Williams' guide lines for high volume air delivery - and with great success. According to their model of 1.2 - 1.5 litres per square centimeter of smelter area, our working volumes have been the range of 500 - 800 l/min. (against our typical base dimension of 25 - 30 cm).
Williams had reported that Michael Nissen (of Denmark) had been undertaking working smelts at volumes in the range of 300 l/min. This is with a blow hole set up and using a version of the Norse double bellows. (His unit is about 50% larger in physical dimensions than my blacksmith type reconstruction.) One thing to note here is that Nissen's set up has the bellows tube sitting just slightly outside the actual blow hole. This may create an extra air intake, from a possible venturi effect from the blast of air. This effect might be increased because of the way air flow pulses under the physical action of the double chamber set up.

Our own experience (admittedly only a single test) of the blow hole set up suggests that this effect may in fact be limited. Note that the last test used the electric blower, which delivers air in a constant blast (no variation cycle):
- When the charcoal was first added, a significant volume of the applied air did not penetrate into the furnace, but instead heated air splashed back out of the blow hole.
- As the internal charcoal slowly ignited, this black splash effect was visibly reduced. This suggests there was some natural draft effect from the rising hot gasses within the furnace.
- The high temperatures within the furnace fairly quickly started to melt material off the interior wall above the blow hole (stone surface). The slag produced then dripped down - freezing when it hit the relatively cold air a the mouth of the bellows tube. This effect was seen at roughly 30 minutes into the main smelt sequence. After about a hour after the addition of charcoal this melted slag had effectively blocked over the entire surface of the blow hole (save for the actual mouth of the bellows tube).
- In that test smelt, there was no attempt made to remove this solidified material. The normal care was taken to ensure the actual mouth of the tuyere remained clear (by rodgering the opening to remove hardened slag).
One question here would be - In the Nissen smelts, was extra care being taken to keep the whole of the blow hole surface clean of slag? I took a second look at some of the images from one of these smelts, and in fact the bellows tube fits snugly into the hole on the front plate. This suggests minimal air loss and no extra venturi effect from the blast.

Monday, October 15, 2007

Icelandic Smelt ONE - published images


This has the images from the weekend's effort plus their brief commentary at this point. I'm still working on the full description and formatting up the experimental sequence details.


TIME - preheat two hours / main smelt four hours

CHARCOAL - 270 litres

ORE - 11 kg

BLOOM - 6 kg

Keep tuned - what was learned this experiment will be directly applied to the Oct 27 smelt.

Thursday, October 11, 2007

Support Our Troops Ribbons

For some time now I have been trying to get one of the 'Support our Troops' car decals. I have just not had much luck with this. From truck stops to Canadian Tire - no one seems to actually sell the things. A couple of weeks back I was talking to another blacksmith, Don Shears, who recently returned himself from a tour in Afghanistan with the Canadian Forces. A couple of days latter I got this source for the ribbon stickers from him:

... you asked about the magnetic "Support Our Troops" ribbons.

Below is a link to a page off of the Canadian Forces Personnel Support Agency (CANEX) website, listing a massive variety of S.O.T's items (I didn't know how much of that stuff there was until I looked!) About halfway down the page are the ribbon magnets.

The cost is minimal - less than $8 with the postage and the taxes all together.

Worth doing...

Monday, October 08, 2007

Thanksgiving smelt - Draft report

This is just a fast overview of the smelt on Sunday October 7 - carried out by Neil and myself.

The smelter was constructed as had been discussed in earlier posts. Neil had gathered a donation of pre-mixed pottery clay (donated by Potter Supply House in Kitchener). This was cut into slabs roughly 6 cm thick, each trimmed to allow them to be stacked into the cylindrical shape of the smelter. The seams were 'mortared' using the wast 'smelter clay' that Selena has provided.

At the front of the smelter, the structure was built up from stone slabs. The lower section was raised to a level of roughly 20 cm. Two smaller pieces were laid on top of this, leaving a central slot about 5 cm wide by 7 cm high. On top of this was placed a large slab - 4 cm thick by roughly 30 cm tall, which was 30 cm at the lower edge and 20 cm at the upper. This slab sits over the zone of the smelter that is subjected to the highest operating temperatures.

The tuyere was mounted so that the tip of the steel pipe was set to just even with the inside surface of the smelter (the edge of the upper stone slab. For this experiment, the standard 22 1/2 down angle was used. Air was delivered via our standard blower, with the rate in the higher volume range that has proved successful in our earlier smelts.

The smelter was constructed on Saturday, and left for the moisture inside the clay to at least partially stabilize over night. This step turned out not to be as effective as was hoped.
The overall set up - during the preheat phase.
Because of the use of block clay (in replace of the standard cobb mixture) a longer than normal preheat sequence was undertaken. Split wood was burned using natural draw for about 1 1/2 hours. A low air blast was then applied for a further 25 minutes before filling with charcoal to begin the primary sequence. The higher temperatures created by the air blast to the wood drastically effected the clay. As the internal dampness flash heated to steam, serious spalling (in fact explosive shattering) of the clay bricks was the result. This so seriously damaged the top course of the clay blocks that this layer was removed and then replace with the sheet metal cylinder used in past smelts. This allowed us to maintain the normal working height of the smelter (adjusted total was 60 cm above the tuyere)

For this smelt, there was not a fixed base of charcoal fines established at an optimum level. Instead, the bottom of the furnace (packed earth) was allowed to accumulate a layer of ash and charcoal from the pre heat materials. In the end this would effect the position of the developing bloom.

Although the smelt was started with a reduced air volume, we fairly early on decided to return to more familure methods - so increased the air delivery to the range of 600 litres per minute. With this higher air flow the charcoal consumption was in the range of 8 - 5 minutes per standard bucket.
Neil taking an 'up the kilt' shot - nearing the end of the main sequence.
The ore used was the commerical hematite grit. To reduce the tendency of this smaller particle size to absorb excess carbon in the reaction zone, the ore was added as a single scoop sized slug, spread evenly over the top of the smelter each time (as opposed to layering it through out each charcoal bucket). It was decided to aim for a historic sized bloom, so a rough total of 11 kg of ore was used.

The primary smelt sequence (first charcoal to extraction) took about four hours.

A top extraction was undertaken, again represented the process we expected may have been used in the archaeological setting we are working towards. There was a clear knob of slag produced at the tuyere which was certainly melted stone from the front slab. This turned out to be a different composition than the normal slag bowl material - with a significantly different melting temperature.
The slag bowl and bloom had also formed somewhat lower in the furnace than has been the case in the past. Both these results made finding and extracting the bloom a bit tricker than in past experiments.

In the end, Neil pulled the resulting bloom. The weight was about 6 kg (roughly 45% return). As has been the case with other uses of the hematite ore, the exterior of the mass was fairly crumbly, but with a clearly solid core.
Remains of the smelter after extraction. The bloom is to the upper right corner.
Todays work is to excavate and record the structure of the furnace after it has cooled down. What is discovered can be compared to the archaeological evidence from the site at Hals.

Thursday, October 04, 2007

Data from Williams & Nissen smelt

This is some information (borrowed with permission) from Skip Williams - reference his smelting trip to Europe spring of this year (March 2007). Skip was kind enough to send me his draft report on the experiment, featuring the use of the tuyere plate / blow hole system.

The smelting experiments were conducted in an oven similar to the one in the picture below. This design is Michael Nissen’s interpretation of the Espevej Oven which was used in parts of Denmark in the period from 200BC to 200AD. The oven has a diameter of approximately 30cm and a height of 50cm above the blowhole. Air is supplied to the oven through a blowhole in a thin plate that is luted into the oven at the start of each smelt. Reports of Michael’s experiments with this design, in English and Danish, can be found at

The blowhole plate is made of a mixture of local sandy clay and horse manure. The aim is to make the plate as thin as reasonable so that it will not melt in the extreme heat that occurs in this part of the furnace. The plate we used was 30cm wide and 40cm tall. It was approximately 4cm thick. The diameter of the blowhole was around 4cm. Air was delivered from a blower through an air tube that rested on rocks and turf placed in front of the furnace.

This information from Skip, and what is visible on Michael\s web site, is interesting in a number of ways that relate back to our Icelandic furnace experiment series:

1) The general concept of the use of a thin / fire proof section at the tuyere. By controlling the way heat develops over the parts of the furnace that are subjected to the highest temperatures, it is possible to reduce the structure at other places, where temperatures are not as high. (We have seen this same pattern develop, This is especially clear on the bricks used in the EconoNorse test smelter.)

(Skip's photo of the resulting bloom - after sectioning)

2) The quality of the bloom produced. Note that it has a much higher concentration of slag within the mass. You can clearly see how the 'bubbles' of deposited iron have grown inside the mass, slowly filling in and squeezing the slag out as they form. If you compare the cross section from the \proto bloom\ from the first VA smelter at Early Iron 1, you can see an obvious sequence.

I will be using Skip & Michael's layout for the Thanksgiving day smelt. The rock slabs will cover from base up to about 30 cm above the tuyere / blow hole space.

Rural High Speed (as if!)

Like usual - way too little and way too late...

Grey County Broadband Initiative

Grey County was chosen as one of the successful applicants in the Rural Connections …The Ontario Municipal Rural Broadband Partnership Program.


Geoff Hogan, Director of Information Technology
The Corporation of the County of Grey
595 9 th Avenue East
Owen Sound , ON N5K 3E3
Phone: (519) 372-0219 x284
Fax: (519) 376-5640

Just a side note to my faceless survey entry:

I just finished investing some $1000 in a direct satellite uplink system for my home. So unfortunately this initiative comes as way too little and way too late.

Our original internet access was via direct dial up. I have been involved in computer based communications longer that there even was a true internet - starting with simple bulletin board style messages in the late 1980's. Our first provider here in Wareham was via Ambassador out of Shelburne.

Through this all, we have been badly effected by the lack of quality provided by Bell Canada wires. As the internet and computers themselves sped up - our hook up cable degraded. In simple terms, as a true rural resident (not in a town or on main road) the same piece of copper wire remains in place. This while the number of physical homes on our road has doubled, and I dare say the individual service demands per house have quadrupled. Run the math and it is clear the Bell Canada wire does not carry the load.

One of our two phone lines to the house tends to deteriorate whenever we have a day of rain. Often to the point of not being able to function at all - completely dead. If you have ever tried to call Bell service you know the problem. A call centre in India of all places, staffed by people who are nice, but have little technical knowledge and certainly no concept of the physical realities of Central Ontario.
Our working download speeds here were in the range of 2 kps or less. Our modem has the potential to run at 56. High speed is considered to be in the range of 100 - 200. True top end speeds as much as 5 MG (thats 2500 times faster than what we get here via the Bell wire!)
We have six different computers here, all different platforms, operating systems, modems and browser software. ALL of these get that same slow access speed. I have linked these via any number of dial up access numbers and through different service providers. Always that same 2 kps or less. Everyone who lives on the section of Centre Line A running west from the Wareham crossroads has the same problem.
Bell insists there is nothing wrong with the lines (even though the phone itself fails in wet conditions). I have demonstrated this to the technician from Bell by hooking up a lap top to the bare wires where they come out of the ground to the house - and still Bell insists there is nothing wrong with their phone lines.

I have generated almost 100 percent of my home based business income directly off my (huge) web site for the last two years. I am an artisan blacksmith, and this income includes direct sales of educational DVD, recruiting students for courses, custom commissions and international museum work. Without the internet I just would not be able to support this business.

I had researched other possible connection methods. I was told that I could access direct wireless service - but to do so would require the installation of an 80 foot tall mast for the receiver head. Since local building codes do not permit me to install anything to that height on my long narrow lot - this was impossible. (Not to mention the cost involved!)

So my only option was to fork out the money for purchase and installation (total of $800) plus other hardware upgrades (another $300) to access the Xplornet direct to satellite system. The cost for this at even the base level is $60 per month. Note that the cost of my dialup ISP was a mere $20 per month.

I have been forced to make this investment and absorb the ongoing monthly cost because of the critical importance of internet communications to my business.

Perhaps the best and most cost effective program that could be put in place would be to offer some kind of grants or rebates against the cost of the hardware and installation of such systems. As has been the case for most of my life - my own forward thinking and independent actions will prevent my access to such a program. Staying ahead of the curve has always meant paying out of my own pocket.

Bell Canada needs to also be hit - and hit hard. Their instance that pathetic quality service to rural customers is acceptable - despite the fact that they impose an additional monthly fee because of our rural location - is at best dishonest. Yet again the profit motive and urban density is at the real core of this refusal to even acknowledge the existence of a demonstrated problem with their equipment.


Wednesday, October 03, 2007

Riverdale House - 1st Install!

For those of you following the continuing saga of the Riverdale House railing project...

The complete process of this major commission (for me) has been documented on the web site: I decided to to this mainly to provide the customers with an ongoing record of the work as it progressed, and also to have a well documented series I could use to illustrate to future clients just what is involved in the creation of such a project.

Just this week the first two finished panels were installed on the house in Toronto

These two images of the pair of flat panels give some idea of how the overall design works in on the front porch. The upper image shows the way the thin flat bars tend to visually disappear when viewed from directly behind them. This was a requirement so as not to block the view of the park across the street from the owner's front window.

The second image is taken from an angle. This gives a suggestion as to how someone viewing as they walk down the street will see the full width of the bars as almost a solid wall of contoured shapes.

I had made the panels just slightly smaller than my measurements indicated. As it turned out - the fit was perfect. One of the frames required a thin shim of wood (which I had prepared and brought with me) and the other was bang on.

I am quite pleased with the results. I checked over my measurements for the next three elements and added some details on the exitisting under framing. Next comes building a full sized mock up of the stairs, to which I will assemble the framing for the two hand rails.

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!)

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

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