36 seen at Wareham

Walking through Wareham
the Yard Art Tour

So here's the thing.
I've now been in Wareham over 30 years - also the length of time as the Wareham Forge.
Over that long a time, you tend to accumulate a lot of pieces.
Some of these are concept tests and samples that lead to major commissions.
Some of these are good pieces, that for one reason or another just never attracted a buyer.
Some of these were intended as 'show' pieces, which simply got marred after being repeatedly being hauled and exhibited.
Some of these are 'just because' pieces, using novel techniques or conceptual designs that cried out to be created.

Many are often what any artist considers some of their best work.

For an overview of what is mounted up around the yard :
Go on to the Yard Art Tour

 

For those who are wondering why contributions have been thin of late?
I've experienced a medical, an am pretty much limited to 'one hand hunt and peck' on the keyboard right now.

Setting up for Phase 3 - B

 Those who have been following the recent work have seen a number of commentaries related to the ongoing series of bloomery iron smelts based on elements from the excavations at Hals, Iceland, by Kevin P. Smith. 

The basic undertaking for the phase three experimental series was build a potential Hals type turf / sod furnace, containing a relatively thin clay liner, using a mixture simulating (as best possible) the material found close by that location. The full build was done in mid June, with the first complete firing cycle on June 20. The intent was to subject the furnace to multiple firings, including one after a winter exposure to freeze and thaw.

After the first use of the furnace, there was pretty much the normal expected damage to the front section of the furnace, with erosion of the walls around the tuyere, and breakage at the extraction arch.

Furnace - just at end of the smelt

20 cm turtle - and damage

What was not expected was the invasion of the warm furnace by a large snapping turtle, which resulted in a large section of the front wall section breaking clear. Weather at Wareham has been unusually wet over later June, July and now into August. (This normally a period where there is little or no rainfall = Climate Change!). Although the top of the furnace was fitted with a metal cover, there has been considerable damage to the 'baked mud' outer sections of the furnace walls, plus considerable slumping to the original grass sod surrounding structure. 

Field drawing of the furnace - August 7, 2021
Note combination of metric and US Imperial units (single marked tape!)

Typically, the next scheduled smelt attempt would take place over Canadian Thanksgiving, this being October 10. I have some concern over additional damage to the existing furnace structure, so have decided to undertake the required repairs to the lower front of the furnace, including breaking clear the internal slag bowl which was left in place after the first smelt.

Interior - just after smelt (tuyere still in place - at top)

Roughly same view, slag bowl broken clear

 The slag bowl from the June smelt did nicely resemble those exposed at Hals, a distinctive C shape with a cupped cross section, the front edge broken away where the bloom had been pulled free during the front extraction. The remaining slag broke free of the interior wall surface quite easily, using a chisel tipped bar from above. There was little actual damage to the wall structure from this process. 

Condition of furnace - August 7

As seen in the images and drawings above, a considerable part of the front wall surface had been broken away. 

The original line of the sods can be distinguished as the place where the upper exterior wall changes from smooth to a wrinkled texture. That top area, about 10 cm wide, despite the cover, had been flaking away in the rains. The slumping of the sod structure is obvious here as well. The heat from the smelt had largely destroyed the binding root structure, leaving basically baked earth. Again the rains were slowly washing this earth down and away. 

The original build had constructed a full cylinder of clay, with the stones supporting the arch and tuyere placed to the outside. As a result, there was no exposure of the stones to heat, other than the short time of extraction. The archaeology at Hals indicates fire marked and slag adhering stones. For this reason, in the repair, a set of small flat stones were used to block in the eventual extraction arch, which will expose the inner surfaces to the heat of the lower furnace.

Interior after repair. Dark grey is the new clay added

Lower section, replaced lintel stone with small flat stones filling extraction arch

In the initial build, it proved quite easy to keep the wall thickness to 4.5 cm overall. This simply was not possible when adding new clay to repair sections considered badly eroded, and those locations where the walls needed to be replaced entirely. new material had to be added by reaching up inside through the extraction arch, most often working from touch alone. There are certain to be places where the fresh clay will be much thicker. Additional clay had to be added around the edges of the small flat stones used to seal the extraction arch, as these where chosen from a random pile of available (gniess) pieces. The same granite lintel stone was used as in the first build, only this time it's inner surface will be exposed to the full heat at tuyere point. Once again, this slab serves to support the upper layers of grass sod (total of three).

Finished repair build, tuyere yet to be installed

An extra row of grass sod was placed around the furnace liner, building the supporting structure back to approximately the same level as at the start of the first smelt ( about 65 cm above hard base). Extra dirt was placed in a ring around the top of the sods, with the hope of reducing any fire damage during the next firing. One additional aspect seen in this image is that the grass composing the sods laid in mid June has continued to grow, and least around the edges of the sod cone. 

For this repair, a total of five prepared balls of the clay / sand / manure mix were required, each about the size of a large grapefruit. (This material left over from the initial construction of the clay liner.)

Depending on team availability and other ongoing work here at the Wareham Forge, the hope is to undertake the next smelt in this series some point over the next two weeks...

You mean ONLY with more air?

 Warning : Often when you e-mail me a question, I tend to ramble on at length in reply. Having spent the time (for me typically an hour or more) on an attempt at a full consideration of that question, I will turn the reply into a blog post as well.

1) so you've shown the early medieval iron bloomery furnaces only produce accurate blooms when you push more air in than you can currently manage using what you think was the bellows technology of the time?

 

 What a ball of wax that is! 

I consider the effect of air a big disconnect, especially with what has happened here in North America as interest in bloomery iron making developed.
I consider myself one of the extremely small group that started the whole thing, in the early 2000's. Lee Sauder and Skip Williams are most certainly the very first to seriously undertake and repeat the process, and finally come up with a system that not only produced significant blooms, but consistently. Their objective was not historic method, but functional results - how to get the best yields at the highest density. Modern electric blowers were employed from the start. One very important difference between North America and Europe is over here work with bloomery furnaces has been primarily in the hands of blacksmiths - not archaeologists or re-enactors. Lee's original point of inspiration was African systems, for which there was some 'traditional' recording still available. He would return to this interest into the later 2010's.

Making bloomery iron is an elaborate, expensive, time consuming, and labour intensive process - with a very steep learning curve to positive results. So the resulting metal has a high 'investment' value. Lee has set the 'selling price' of his bloom pieces at roughly $60 CDN / kg (the few times I have been asked, I quote $100 / kg). This is roughly ten times the cost of modern alloy steel bars. So for blacksmiths, the only object type that can justify this kind of investment in materials to object price is knives. Unfortunately, here in North America, this has lead the entire Early Iron movement to become dominated by bladesmiths. This in turn has lead to what I feel is a quite unrealistic obsession with carbon content, an extremely modern consideration of what is clearly a 'pre industrial age' material (and processes).

The 'Gange o Fer' in 2004 : (L-R) Lee Sauder, Skip Williams, me, Mike McCarthy

My interest started with Viking Age systems, most specifically sparked by the single smelt event at Vinland by the Norse. c 1000 AD. As part of the original 'Gange o Fer', it was so clear that there were many individual variables effecting the dynamic inside a small scale furnace. So the early years were simply testing variable after variable, in the hopes of getting some understanding (and control?) over these both individually and in combination. So my focus has never been either to best possible yields or specifically 'quality'. If anything, my estimate of 'good iron' is based on the ease of compacting the bloom to bar, then the ability of that bar to be easily forged to object. Yes, we do end up with some blooms to bars being higher carbon, and set these aside (as the Norse would have) for cutting edges.
Through almost all of our experimental work, we have quite deliberately aimed to making smaller blooms, in the 3 - 5 kg range. (Yield % climbs sharply with larger ore volume additions!)

In Europe, much of the work with bloomery iron is in the hands of living history sites and hobby re-enactors. What has been so frustrating to me is the lack of recording. (See my piece in EXARC : 'Standardized Reporting...'). Lee has pointed out to me many times the overall difficulty of getting any kind of effective measurements of air volumes, and that the only uniform field reporting can be 'time of consumption'. Even there, it is obvious to me that most people are actually reporting total charcoal consumed / total time of smelt. This is actually only a vague average at best.

One one major problem is the simple lack of historical accuracy I see. If you are using what is at best a Late Medieval double chamber bellows (to chambers stacked on top each other) you are NOT using 'Viking Age' method. Too often I see smelts described as 'Viking', which are using different furnace builds and ore types, than the known Norse archaeology. *

Our 'Econo Norse' teaching furnace : Brick, pipe tuyere, vacuum blower, using taconite. The only thing 'Viking Age' is the furnace diameter?

Don't miss understand - people are most certainly getting iron blooms. 

The times we have used a proven furnace layout and standard ore, yet with variations of a Viking Age type twin chamber (side by side) bellows, consistently our yields drop about 10 % overall, from an expected 20 - 25 % down to closer to 12 - 18 % return. The blooms also tend to be considerably less dense (so harder to work into bars, with more loss at this stage of the overall process). 

Early twin bellows for smelting ? : 'Ubber-Bellows' for CanIRON V prep, 2005

- Obviously, one clear possibility is that the whole furnace layout and overall method we are using is just not effective, and so may be entirely different than historic process. (This might also be a simple as 'we still are screwing up'!)
- We are working with an Fe2O3 based ore analog at typically about 55% Fe content. Natural primary bog iron ore is actually FeO-OH, which potentially could be as much as 63% Fe. Natural ores vary considerably, even from the same location, but the difference between both chemistry and especially iron content may be a significant difference?
- We have certainly found a considerable 'learning curve' with use of human powered air. It may be that we are just not working correctly with this entirely. (One experiment using a secondary collection bladder may be suggestive, but there is nothing from archaeology to suggest this method. Latter Medieval illustrations which do show bellows use, don't show bladders. )

Norse 'blacksmith' size bellows linked to a bladder : SCA 50 event 2015

So key to this whole thing is a more correct statement :
 'We don't get historic blooms when we use Viking Age suggested bellows.'
- There is not much data available on the actual measured density of the existing artifact blooms.
- Others are certainly getting iron - but there is often no clear reporting of actual yield or most importantly the quality of those blooms. 

* What REALLY aggravates me is a most recent trend to individuals who are using 'Viking Age!' as a mere marketing label.

Icelandic Clay Mix Test - the full smelt

The following is a fast overview of the bloomery iron smelt at Wareham, June 19.

This experiment has the DARC team return to our experimental work based on elements of the 'industrial' Viking Age site at Hals, Iceland, originally excavated by Kevin P. Smith (1). The earlier work can be loosely divided into two phases (2) :

- Phase One / four experiments / 2007 and 2008 / testing individual design elements

- Phase Two / four experiments / 2012 to 2016 / testing use of turf builds, combining elements from phase 1

The current work, as Phase Three, centres on:

a) testing clay mixtures based on those from Iceland

b) testing durability of a turf (sod) supported furnace structure over time

An earlier blog post ("Sticking to It - a clay mix for Icelandic?") detailed the logic behind the clay mixture itself.

Part way through the build process

Based on experience from the earlier furnaces of this series, the wall thickness was set at 4.5 cm, measured against 'two fingers' as shown. An internal form was used, metal in this case, keeping the interior diameter consistent to 28 cm. (This replacing what could have been a wooden straight sided 'barrel' form historically). The clay was constructed to the rough top of the form (about 30 + cm), then the supporting cut sod strips were placed in a circle on the outside. The form was pulled upwards, with the exposed interior filled with a mix of half sand / wood ash. This method has been used many times, the ash mix both supports the thin clay and also helps to dry the walls. 

Built at 35 cm

After the first full course was established, a set of small stones, used like bricks, were placed to frame an extraction arch for the front of the furnace. One large piece of basalt on hand was used as a lintel to eventually support the tuyere and upper sod pieces.

With air system, at first charcoal addition

The build continued to raise the total stack height to 75 cm. The supporting sods were laid in five layers, to a height of roughly 70 cm (at the start of the smelt). The cone created was a bit irregular, extending out 72 cm to the left side as seen, to 56 cm to the right side. Although materials (timber and earth) had been labouriously gathered, it was decided not to box the sod cone and back-fill to a flat upper surface.

The extraction arch was 23 cm wide at the furnace wall, opening to 33 cm at the edges of the framing stones. The lintel slab sat on a slight diagonal, at roughly 20 cm high. There was additionally a small tapping arch cut, 6 cm at the base and 8 cm above the hard base. 

There was no specific attempt to match the air system to evidence from Hals, we chose to use our proven heavy copper tube, inset 5 cm beyond the interior wall. As supported on the lintel slab, and with our proven 22 degree down angle, this set the tuyere tip a bit high in the furnace. In turn this reduced the effective stack height to only 40 cm (normally considered a minimum distance). As this position would also leave a lot of space under the tuyere, a 'soft base' was created with wood ash from the drying fire and a layer of charcoal fines on top, raising the set base to 15 cm below the tuyere. The simplest method to support the normal viewing port and air input connection was to suspend it from a metal rod set well clear of the working opening in the sod cone. 

The primary smelting team :

Darrell Markewitz - smelt master

Neil Peterson - ore and records

Rey Cogswell - charcoal / ore

Kay Burnham - charcoal / ore

Richard Schwitzer - compaction

Kelly Probyn-Smith - safety

Travis Sweet - photography

Slag tap. Earth falling free of the upper sods can be seen as light reddish pieces.

Over the 7 1/2 hours of the main smelt sequence, it proved necessary to make at least four major slag taps to lower internal slag levels threatening to 'drown' the air blast. 

Later into the smelt, it was clear that furnace heat was seriously effecting the sod structure. Earth was baking dry, and pulling free from the root systems and falling downwards between any cracks. This would cause the whole sod cone to slump into itself by the end. There was no venting of furnace gases observed however.

Air flow had been purposefully reduced for this smelt, down to a range considered possible for a human operated bellows of Norse type. Although the long serving electric blower was used, air flow was initially set to roughly 700 LpM, increased about the mid way point to 800 Lpm. (3) This would create an average burn rate at 8 minutes per kg over the main sequence. 

Initially 5 kg of previously gathered iron rich tap slag was added to establish a working slag bowl system. This may have also contributed to the need for later tapping. A total of 25 kg of the DD1 analog ore (51% Fe) was used with combined average addition rate of 11.8 minutes per kg.

Pulling the bloom mass free. Image by Travis Sweet

The bloom mas proved much larger than expected! In pulling it clear of the furnace, the supporting lintel stone was pulled away, resulting in the upper sod layers at the front of the furnace also collapsing, exposing the front furnace liner.

Classic compaction shot - Darrell holding, Neil on sledge : Image by Travis Sweet

With loose gromps hammered clear, before cutting on the press : Image by Travis Sweet

I

To everyone's great surprise, after some first stage compaction and rough cutting, the resulting bloom, although a bit loose in texture, weighed in at 8.9 kg. This represents a 35% return from ore (4).

 

Furnace, just after extraction / compaction, with remaining slag bowl seen.

On a quick examination of the furnace (after our ritual post smelt Guinness) :

- The furnace still contained about 2/3 of the slag bowl, completely filling the interior save for a large piece broken away at the extraction arch to expose the bloom, creating a clear C shape. The depression towards the air blast side clearly frames where the bloom was pulled free. The slag bowl remaining is of a size and shape quite similar to those exposed at Hals.

- The front portion of the furnace has clearly broken away, when the supporting stone lintel pulled off, as the bloom mass was finally pulled free. The image above shows it's natural fall position. The sod that had been above this has pretty much totally crumbled away into it's containing dirt.

- There is considerable slumping of the encasing sod cone. The clay liner had actually lifted slightly several times while working the bloom free, but had remained as a solid structure overall. 

Largest of the roughly compressed and cut bloom pieces : 3 kg

to come : looking closely at how the clay walls survived the smelt

 

1) Smith, K.P., 2005, "Ore, Fire, Hammer, Sickle: Iron Production in Viking Age and Early Medieval Iceland", AVISTA Studies in the History of Medieval Technology, Science, and Art, Volume 4, USA

Also available as PDF on line : https://www.academia.edu/191535/Ore_Fire_Hammer_Sickle_Iron_Production_in_Viking_Age_and_Early_Medieval_Iceland

2) A overview of both the Hals site and these experiments is currently under preparation, co authored by Smith, Markewitz and Peterson (‘Now with 70% Less Clay! Experiments with Viking Age Icelandic Turf walled Iron Smelting Furnaces’) A short video overview was presented at the recent EAC 12 virtual conference, available on line : https://youtu.be/7Ltz5NG2BP0

3) For a furnace at 28 cm, the normal air flow would be set to closer to 900 - 1000 Lpm. see : Air Flow Rates

4) This impressive result may be the effect of the 5 kg of iron slag added as a first step. Our past results for smelts in the 35 - 30 kg ore range have more typically been roughly 5 kg (or less).