The Heat was HOT...

(...and the air was dry...)

Another piece from ongoing discussions on Don Fogg's Bladesmith Forum - Bloomers & Buttons

Jur wrote on 16 January 2013 :

One of my best bloomery results was when I charged the ore straight from the roasting pile into the furnace when it was still red hot. This could explain some of the lower shaft furnaces. Anyone else tried this before?

Some of us here have experimented with different furnace layouts and builds.
There is a relationship between your furnace design and the 'best possible' air volume. Tuyere placement also comes into this, as it will define the shape of the effective heat zone at the bottom of your furnace. That air (oxygen) volume will both ignite a certain amount of charcoal, and produce a certain volume of reactive gases. Both volume and placement are important influences on the quality of the final iron bloom.
If your furnace is BIGGER than the effective 'ball of chemistry' - then there is no actual reduction of the iron oxide occurring at the very upper part of your furnace stack.
What *is* happening is that the materials involved in the smelt (both ore and charcoal) are 'pre-heating', so more or less flash straight into reduction once they hit the heat zone and available reaction gasses.
(Clear as mud - right?)

So, Jur, your mention of lower shaft furnaces is the key to your suggestion.

I think those of us who have build 'medium shaft' furnaces have noticed that there is a significant increase in efficiency. Adding even 10 cm extra in stack height can really increase bloom yield measured against charcoal consumption. The ore is being heated in this upper zone.
So, I think (as much as my brain works) you have hit on a possible way to improve the workings of low shaft or bowl furnaces. (Those with heat zones effectively *smaller* than what might be possible through ignition.)

'Boxed Bowl' - L'Anse aux Meadows 2001 (first smelt)

There had been some related conversation of late - in reference to the Evenstad system. This uses small pieces of raw wood as the fuel. The waste heat then converts the wood into charcoal before it hits the combustion zone.

One thing though does occur to me:
If you took your ore straight from a roasting fire into the smelting furnace - does that not make breaking the ore for correct particle size just a wee bit difficult?
The correct ore size (depending on type and furnace layout) is one of the major variables for a successful smelt.

More on the Evenstad Furnace

Continuing the ongoing discussion on Don Fogg's Bladesmith Forum.

This related to the descriptions of a wood fired bloomery furnace and a re-melting hearth, by Evenstad in the late 1700's:

Mark Green, on Don Fogg's Bladesmith Forum - 08 January 2013 - 11:47 AM, said:

Anyway, that looks like a very cool experiment to try.
I still have my doubts about the wood converting, as well as reducing the ore, with one load. I would think, it would take some continuous feeding of wood and ore. I don't like that there seems to be no slag tap.

I was working within eyeshot of Ole Nielsen  at the Heltborg Symposium (2008). Unfortunately, I had shot video of his process, via a camera which destructed and destroyed the footage. So I have only a few still photographs of the build and more importantly of the furnace in action.

Those who have run a smelting furnace have certainly noticed that the hot spot over the tuyere will consume the fuel on that side faster. This can result in a slope to the charcoal at the top. (Why you end up charging in a horseshoe around the far side of the furnace in the later stages of a smelt.)
The version of the Evenstad that Ole constructed was something like 2/3 scale. It was roughly a meter wide and a meter deep. It did in fact appear a bit wider than deep, so not quite the same proportions as the manuscript illustration shows. There was also not as pronounced difference between the top and bottom diameters - so in turn not that more trumpet shape seen in the illustration.
I suspect both of those aspects are important.
What I observed was that the surface of the raw wood packing was making the same slumping pattern over the tuyere side. So in effect, the raw wood from the back was travelling along a diagonal line - which certainly was giving it time to transform into charcoal. This in effect utilizing the waste heat from the smelting process.

I agree with what Mark comments on the lack of slag taping. There may be something going on with the size of the bellows system - related to force of blast and volume of air. Most of us in North America, if working with European types furnaces, are using the 'Sauder System' of high volume air. This puts the bloom below the tuyere, towards that side. The Europeans are often working with lower air volumes. This appears to move the bloom higher in the furnace (and produces a more lacy, smaller bloom as well.)
As you suggest, more direct experimentation with the Evenstad system is needed to really understand it.
We also need to remember that those illustrations are certainly 'ideal' - and may not actually match the functioning furnaces in fine detail!

My understanding from the manuscript is that this system makes a series of smaller blooms, in a continuous process running over several days (!). It describes pulling away excess slag (the bowl) after each extraction. Remember that this process is linked to use of a primary bog iron ore as well, which depending on source, might contain a lot less silica than the rock based ores that those of you from the eastern USA are used to using.

Under 'Conclusions' Evenstad says : "Smelting 24 pars of ore gives 36 lbs of raw bloom. Output should be 150 lbs per day. ... Three men can do five smelts a day."
Espelund notes that his own experimental trials suggest 4 hours per cycle, so that is a 24 hour day. Running the math gives us roughly 30 lbs for each bloom / 15 kg. So large, but not immense. Espelund describes a test he ran in 1991 had 15 kg of ore produce 6 kg of bloom. (Thats a very respectable 40% yield, but of course the ore quality is critical.)

Mark continued  - Referring to 'Iron Production in Norway' - Arne Espelund

Is there a full description of the operation of it in that book? Which is no where to be had, at any price that I have found in the world.

Not overly surprising. I think the Espelund book was almost 'vanity press', and I doubt all that many were printed. The publisher is Arketype in Trondheim Norway. The frontpiece states "The printing has been financed jointly by the Norwegian Metallurgical Society, INFACON, and the Historical Metallurgy Society in England" . Maybe some leads there?
I managed to score a photocopy directly from Arne when we first worked together at a workshop for Parks Canada in 2001. (Which got me started in this insanity.)

Iron in Norway devotes about 20 pages to the manuscript and Eslplund's comments on it. There is another 10 pages of background material.

What might surprise you (??) and is most specific to our starting point here :
The actual reference to a re-melting hearth in the Evenstad is very short and not overly descriptive. Its only a single paragraph!
I've scanned that specific section and attached it to the bottom of this.

The whole bladesmithing community owes a huge debt to Skip Williams, for researching and prototyping the first 'Aristotle' furnace. Then to Lee Sauder, for hosting the Early Iron group at Smeltfest 08 where we were introduced to this prototype. Jesus Herandez, Shelton Browder and Steve Mankowski, (and myself) for the week we spent figuring out how to make the system work and control the variables.

Blast from the Past - in Black & White

A piece of trivia : I had originally entered art school with the full intention of becoming a high school teacher. Bill Davis and the education situation in the late 1970's in Ontario had other ideas.
The result was an intentional drift through a number of departments and mediums. You see, the very best art teachers I had ever had where not the masters, but those with the widest understanding. Those with enough background in an area to inspire students and show them the basics. Then the wisdom to turn us loose to explore, advising as was needed to prevent pitfalls and keep us inspired.

The only studio I took for each of my four years at Ontario College of Art - was Photography.

'Bridge' - 1975 (Trent University - Peterborough)

'Reflections' - 1975  (future Harbourfront site - Toronto)

'Pebbles' - 1976 (Mclaughlin Planetarium - Toronto)

'Solar Flare' - 1976 (solarized image, waterfront area, Toronto)

These did not have titles originally. The images are scanned from the b & w prints. Out of thousands of negatives, I only ever printed and mounted a mere handful.

Hearth or Furnace?

Re-cycled from an ongoing discussion on Don Fogg's Bladesmith Forum : Bloomers & Buttons

Posted Today, 07:10 AM

Mark Green, on 07 January 2013 - 04:35 PM, said:

The Evenstad hearth is a relatively shallow. With the 'high' tuyere level being 3 in. above the floor, it doesn't need to be more then 5-6 in. deep max.
...
The one depicted on Darrell's site is a smelting furnace. Much like a Catalan smelter. It is MUCH bigger then a hearth smelter....

So, sorry if this seems way to elementary, but I'm bearing in mind my own (lack of) experience in this specific area (re-melting hearths) - and the variation in background of the various readers.

The Aristotle Re-melting Furnace:

This is Lee Sauder at 'Smeltfest 2009' (This is the invitational research week Lee has hosted for a small group for a number of years.) That year Skip Williams introduced us to the 'Aristotle Furnace', which we worked with over about 30 plus test firings, building maybe a half dozen different layouts. (see a brief report : http://warehamforgeb...y-overview.html )
This is obviously a furnace - and a re-melting furnace (rather than an ore to metal 'smelter'). What it produces is a small puck of mid to high carbon metal, but with some of the slag inclusions and texture of a bloomery produced material. As Jan so correctly states, the source metal can be almost anything. We have tested this using pieces of mild steel bar, bits of cast iron window sash weights, old corroded wrought iron scrap, fragments of bloom - even nails and beer caps (!) The carbon content of the end product depends on the set up of the interior bottom of the furnace. You can both reduce *or* increase carbon content, depending on the bottom depth below the tuyere and the angle of blast.

This system I have run maybe 50 plus times over the years. (Use the search function at the top for 'Aristotle Furnace') Although I did put together a basic 'how do it' handout, I know there is good information available from Lee and Skip:
Descriptions and further reading on the Web:

"Teeny-tiny Bloomery"
by Skip Williams

"A different way to make steel"
by Jesus Hernadez (on 'Don Fogg's Knife Forum')

Aristotle's Steel
by Lee Sauder (PDF download)

"Steelmaking in a tiny open furnace"
Donald Wagner (This is a photo essay from the same event that Lee's article above was based on.)


Because of the way this post works, I'm not sure how the order of the next images as attachments:

Re-Melting Hearth

The image is of Lee's experiments at Smeltfest 2012. The first I saw him working with that system was at Smeltfest 2011, working with Tim Young from the UK.
Note that I personally have never built or worked with one of these. This is also the core of the discussion here (!)
For that reason I am not going to attempt to describe how it works or what is going on - or the quality of the product. Mark certainly is covering that information (and well!).

Just for interest - although it is sideways to the main thread (and people have mentioned it)

Evenstad Bloomery Iron Furnace







This image is from Espelund's 'Iron in Norway', but is a reprint of the original 1782 manuscript illustrations by Evenstad.
One important note : The scale is in 'ells'. Think roughly the distance from your elbow to your finger tips with fingers extended. Given other places in the document as '60 cm'.
That makes the conical furnace roughly :
60 cm at the base
10 cm from base to tuyere
180 cm at the open top
120 cm deep
This is a wood fired furnace. The description states small pieces of wood would fill the furnace before lighting. The heat of combustion converts this to charcoal. Once this is accomplished, then the ore is added.
The furnace is intended to be a continuous cycle of production. Ore is added, reduced to a bloom. At that point the bloom is fished out from the top. The excess slag mass is cleaned, then the still hot furnace is filled with another charge of wood to repeat the process.
The bellows shown are two long narrow chambers, lifted with spring poles. A worker stands on top of the plank extensions, shifting his weight side to side to operate.

The source reference is:
Arne Eseplund : 'Iron Production in Norway During Two Millenia'
1995, ISBN 82-992430-3-3

At the 2008 Heltborg Symposium, I saw Ole Nielsen and his team build a version of the Evenstad Furnace and operate it. Ole is to the left, blue shirt, gloves with long bar.  (for more images see http://www.warehamfo...BORG/index.html ) This was still early in their experimental series, and although they did manage the wood to charcoal element, and produce a large slag mass, there was little iron produced. (Most of us had low or no yields, I think the ore we were using was to blame.)


This all started with Mark Green describing some of his recent experiments / tests using a deep hearth to refine and change the carbon content of his blooms. The conversation drifted a little, towards defining terminology:

Jan Ysselstein, on 07 January 2013 - 12:32 PM, said:

I have begun to associate a hearth as a furnace where the bottom plays a significant role.

 This is a very nice, clear definition.

As frequent readers know, the problem of use (and mis use!) of metal working terminology is a big concern for me.