Tuesday, August 21, 2018

'You can't always get what you WANT...'

but you get what you * PAID FOR *

On 2018-08-20 7:46 AM, N. S. wrote:
I recently received a damaged “Sword of Saladin and Scabbard” made of 1065 High Carbon Steel:
from the original seller's web site (1)

By Windlass (meaning made in India).
Here is how Windlass describes itself (taken from their own web site)
Founded in 1943, Windlass is today the premier supplier of military dress and sabers and accouterments, motion picture props, and a whole lot more. We are proud of our military contracts with governments in six continents and the excellent replica props we deliver to Hollywood’s biggest blockbusters.
You will not find this specific item still listed on the actual Windlass web site (2)

Check around the inter-web:

From the Museum Replicas web site:

Sword and Scabbard of the Great Saladin

from the Museum Replicas web site
$444.95 US

This sword has the unique "fork tongue" blade crafted of 1065 high carbon steel. Features 24K gold plated pommel and cross guard. Includes wooden scabbard covered in leather and accented with 24K gold plated fittings. Overall length of 41-1/2 inches. 

a) Any time the description and the product images centre almost entirely on the *furniture*, not the actual *blade* you had best understand what you are paying for is the *flash* NOT the *function*.

b) The blade description? *Crafted* is what it says. Not *forged*. Not a word about the heat treating. Best assume this will be perhaps a suitable (if simple) metal alloy. But most likely ground out by machine from annealed bar stock - with no hardening or tempering undertaken. Meaning not at all *combat* ready. 
(I do realize that this was not the question given to me!)
c) This item is shown as discontinued (Museum Replicas & original seller). It is not listed or described on the actual Windlass site at all! 
What was not provided was if this purchase was made at the full retail - or at some discount. If at a discount - then 'buyer beware' certainly needs to apply.

Both edges of the sword and the scabbard. I tried cleaning it with Lysol, Windex, Brake Cleaner... nothing worked. Took it to a local blacksmith who only works with military swords and he was able to remove a lot of the gunk on the blade, but scratched the sword in the process. Please see pictures.
image from N.S.

image from N.S.
image from N.S.

So here is the problem:

If the corrosion effect I see in the image (just by the lion pattern etching) is the problem?
You should have returned the blade to the seller and required a replacement.

The marks look suspiciously (to me) like finger print created corrosion. (Touching the blade and not wiping it off afterwards.) This is a corrosion / rust deposit right into the steel. The surface is actually pitted.
The only way to correct this is to re-polish / grind the surface down below the level of the pitting.
Normally this means reducing the level of the surface down for the entire length of that edge. Otherwise there will be a noticeable 'divot' at that point.
Do note that the imperfection is right beside the etched design.
How to shave the surface down below the pitting - without actually effecting the shallow etching?
You might be able to remove metal just at the pitting, by carefully using a set of small grinding / polishing burs via a dremmel style tool just at the corrosion site. Given the high surface polish down the rest of the blade surface - this will always reflect light differently - and so be visible.

1065 carbon still will *always* rust - unless you constantly keep that surface lightly oiled. Even WD40 would prevent this.
Fingers touching the blade surface are to be avoided on almost any steel surface - especially carbon steels.

The first bladesmith has cleaned out the existing corrosion. That pitting is right into the metal at this point.
The surface has been scratched? To be expected unless the entire blade surface was ground down below the pitting.

'Made in India' ? (2)
To ship items overseas, usually some kind of lacquer is applied to the metal to prevent surface corrosion during long shipping. These coatings are often not evenly done. Removing the *lacquer * sounds like what you attempted. (Noting that none of the solutions you applied will effect lacquer - maybe try actual 'lacquer thinner'?)

Overall ? - I am not surprised.

I would be quoting in the range of $600 + : JUST TO FORGE THE BLADE.
The cost of the elaborate carved hilt, cast cross guard would easily push the quote into the $1000 + range.
This is a mass produced item - made 'offshore'. The selling cost reflects this  - and also the relative quality for that price.

And no - I would not be willing to undertake the kind of repair work being requested. (3)
a) With corrosion pitting into a metal surface, there is no real way to completely remove this - without also visibly effecting the surface.
b) The imperfections on the thin 'gold' plating on the hilt detail are either a result of poor application of the plating at manufacturing, or possibly damage after the fact. In either case, the underlaying metal (likely brass) would have to be re-finished, then new plating applied. This involves taking the metal collar seen completely off the sword. Given how gold reflects off surfaces, this also makes it likely the repair would also be obvious afterward.

(1) I have deliberately NOT cited this supplier - who is also in the business of selling primarily *costume* pieces. I have personally ordered various things from them in the past. With care in selection, my choices have represented good value for the reduced prices. I have found their service excellent. My working relationship with that company remains very good. 

(2) Look - this company does have a 75 year history. There are smart people in India, and family operations there who have been making blades for *hundreds* of years. This is not intended as a snark about 'made in India', in any way.
Look what Windlass actually specializes in, makes and sells. 
*Costume* pieces. 
Even their 'Military' lines are *dress* blades - not *functional* weapons.
(The exception to this may be the 'Kukris' they have described as 'Genuine Gurkha Regimental'. This appears to be how Windlass established its original reputation. They do provide detailed specifications for these blades, but the low price (quoted at $50 US) makes this perhaps questionable?

(3) Increasingly, I get requests to 'beat the price' or 'fix the mistake' related to what are nothing more than cheap 'wall hangers'. Surprisingly - I am not at all interested. 
Please take the effort to at least look at my body of past work, and decades of experience?

Friday, August 17, 2018

Design via Inspiration (Legge workshop)

As I had posted here much earlier, over the last weekend I took part in a 'Design Masterclass' by Adrian Legge, organized by Sandra Dunn at TwoSmiths in Kitchener.

Honestly, I found the whole experience exceptional. Adrian is an excellent teacher, combining insight and knowledge through a very direct and honest manner. I was especially impressed how he was able to cut to the core - and present guidance well suited to each individual student. The class group varied considerably in terms of technical ability and past experience, but it was clear direction was given to each as best needed.

So - this is the preparation work that was given to each of us: 

Two Smiths design class
Adrian Legge

Prior to the class I would like you to do some Initial Research
You might like to investigate the potential for developing a personal style/creative identity or perhaps you are more interested in looking at a particular design problem such as something that addresses a specific site or uses an established aesthetic style that you are interested in

Collect 25 examples visual information that inspires you, comprising of both primary and secondary source material

A)    Primary source material can be e.g. observed drawings from your sketchbooks, photographs taken by you, actual objects, investigative forge examples etc

B)    Secondary source material can be e.g.  downloaded or magazine images, examples of work by others, research, creative writing etc

Try to avoid just collecting examples of ironwork that you like as this will tend to push you towards working within an existing style

C) As you collect the information to be selective and intentional  in your approach- have a reason for your choice

D) For each example produce a word or sentence that ‘explains’ what you like about it. Try to use emotive rather than descriptive. For example ‘I like this because it reminds me of the spring’ rather than ‘this is a snowdrop’
Choose images and words that excite and inspire you and that you will be able to use to generate ideas and concepts. (1)

And here are the images / objects I chose (2)
These are set loosely by source type, not in order of my initial selection:
A) My own photographs

* 'Chaos Theory' (iron smelting slag tap)
'Combined Elements' (dinosaur skeleton)
'Surprise Detail' (crab on stone shore)
B) Images by others
* 'Colour, Scale?' (fish scales, micrograph) (a)
'Curves' (leaf centre) (b)
* 'Fantasy' (CosPlay image)
'Influences' (Japanese sand garden) (b)
* 'Nature Surprises' (sea mollusk)
'Organics' (natural plant forms)
'Complex Patterns' (false colour of atoms in cloud chamber) (a)
'Patterns, Scale?' (overhead view of settling pond) (a)
'Symetry' (sea creature burrow) (a)
* 'Variation Pattern' (detail of starfish) (b)
 C - Work by others
'Structure from Organics' (Paris Metro, H. Guimard)
'Texture & Material' (Lee Sauder)
'Flow' (the Batersea Shield / Celtic Bronze Age)
'Integration' (Castle Henrietta, H. Guimard)
'Repetition, Influences' (St Padridric's Bell Shrine, Irish c 800)
'Scale' (artist unknown)
* 'Spirit' (Lady of Shalott, Waterhouse)
 D - My own work
'Exploration' (Hector's Bane)
 E) Objects (insets show actual size on enlarged version)
'Antiquity' (water worn / pierced stone)
'Attachments' ('live rock' with kelp)
'Context' (cast bronze, found object?)
'Segmentation' (trilobite fossil)

A couple of things became clear when all the individual images were laid out and viewed together :

* Most of the source images are organic / show organic lines.
* Many of the images show complex patterns.
* A number of the pattern images show the effect of one line on to another.
* A number of the images were chosen for their colour as much as the lines (3)

The two larger format images, (starfish / cloud chamber) were the two sources I ended up settling on for further work inside the workshop.....

(1) Shared in the spirit of education. Text written and provided by Adrian Legge

(2) In most cases, I had collected these images over many years. Please consider them 'scammed' as in almost all cases I can not cite the source / owner:
a) taken from 'Discover' magazine
b) taken from the Mac 'screen saver' collection

(3) For presentation at the workhop, I had printed off each image. Only the ones indicated with (*) were rendered in colour - the remainder printed in grey scale.

Thursday, August 16, 2018

Fire Steels - in theory?

(Taken from an ongoing discussions related to a research project on Viking Age / L'Anse aux Meadows and Vinland beyond / Flint & Jasper strikers / Fire Steels)

I freely admit that making fire steels has * not * been my best thing in the past.

Like many apparently simple things, the metal selection, and actual heat treating, for best results in fire steels is complex.

Quickly (as I understand it) :
The way these work is that the steel resists the tearing action of the stone. The pressure required eventually tears off a splinter, which due to the force heats under impact. Hot enough to actually heat the fragment above the 'burn point' of the steel. This makes the spark, with temperatures in the 1100 - 1200 C range.
Different carbon contents have different shear strengths.
Different carbon contents also have different burn points
You can modify the shear point (strength / hardness) of any one given alloy (carbon content) based on the quenching method chosen.
Different stones themselves will break with different applied force.
So this suggests there is a dance between metal type, making method, and stone selected - combines for best results

Generally my understanding is that a good fire steel would have a high carbon content to the alloy. Here meaning at least 0.05 % (spring), but maybe as high as 0.1 % (file).
But the quench may slightly on the slower side, to keep the result from becoming so hard the stone chosen can't actually shear off that small flake.

(I took a fast look over the past blog entries - as I thought I had worked up something on the topic. Yup - based on something the same researcher had asked about back in 2011! )

   " I may order 2-3 fire-strikers from a couple of sites on Etsy that
   are selling Viking Era types (one site is a forge in Canada, the
   other's in Germany). Those might get us started with some basic
   experiments on how the jasper / chert responds (how many flakes and spalls are generated per 100 strikes, etc.) and of course we'll make
   some sparks, even if we don't have information on the carbon content
   of the steel. "

(site references deliberately removed!)

I think it illustrative that the Canadian chosen does NOT refer to the actual metal type used.
The German does state 'carbon steel' - which is what is needed for correct function.

from Marstein, Uppland, Norway : 7.7 cm. Common 'boat shape' forged from flat bar (Image from 'Viking Artifacts' - Graham-Campbell)
The German also is offering shapes that look more like the actual artifacts I am familiar with.
For this reason I would suggest the German (shipping is the only cost variable).

Readers may have seen way too many things as being named 'Viking' - when in fact they are not even remotely like the real objects! This is a *big* problem for me. Truth before Advertising please!

Wednesday, August 15, 2018

WARNING - Blog being spammed

Readers here may be diverted to a spam advertising site.

I have messages out to both my ISP/ Support Guru and Blogger itself in the hopes of fixing this. (Both front and back door to Google, but given the mass?)

Curiously (?) this does NOT seem to be happening to me using Firefox as the browser access. My own tests using Safari or SeaMonkey also divert. I have had reports of Chrome also diverting (I work off Mac). This does not seem consistent however, some people report no problems.

A paid advertising site : Widget Server (dot) com is somehow grabbing visitors from Hammered Out Bits and shoving them over to some spam styled advertising site. Widget Server obviously 'sells' different spam pages (if you examine the actual URL used, you will see a randomly applied number to different advertising).

I am attempting to fix this - but please bear with me for just now.
I believe the problem lies inside Google Blogger itself.

Thursday, August 09, 2018

Charcoal / Ore / Burn Rates?

On 2018-08-08 2:19 PM, Jeff wrote:
I remember that both you and Lee abide by the 1:1 weight ratio of charcoal to ore. But I can't remember how big and fast the charges were. Was it (like) 1kg every 10 min?

In North America, we normally calculate time per standard charcoal measure.
Most of us us a standard galvanised bucket - which runs about 1.8 kg dry charcoal (sized ) slightly depends on species.

'Bucket on a stick' standard measure (Icelandic / Hals furnace)
The standard is usually 8 - 10 minutes to burn that measure.
Anything below 6 is way too fast - cut back on air
Anything over about 14 is running too slow - increase air volume

The Europeans normally will report kg per hour
(most of us here just don't bother running the math)
The ideal amounts / time works out similar.

On ore
there is typically a ramping up of volume of ore over the progress of the smelt.
My group typically starts with 1 kg charges per charcoal bucket.
At first there will be a slight damping of temperature / increase in burn time as the cold ore works down the column.

A portion of ore charge (analog) added before being covered with a part bucket of charcoal.
Once the reduction reactions start, and the slag bowl starts to form, you should see the temperature / burn time shorten.
Adding increasing amounts of ore will help to keep the burn rate consistent - even though there is more and more ore inside the furnace column.
This makes the 'magic' ration even out to roughly 1: 1 ore to charcoal (by weight)
Expect in the later part of the sequence to be able to increase the amount of ore per charge - with the same burn time.
We usually hit at least a few 3 kg ore to 1.8 kg charcoal. I have managed a couple of times (on much larger total ore amount smelts) to get to 4 kg per 1.8 ! (Our usual is 30 kg ore, so we don't get to those big numbers often).
There is likely a 'type of ore' effect here too. Working with our bog ore analog, we have a high Fe2O3 content, without much silica (rock) impurities.

Thursday, July 26, 2018

Bellows for Iron Smelting (the measurements!)

Recently I was asked by my friend Mark Pilgrim (interpreter at L'Anse aux Meadows NHSC) for the actual measurements of the iron smelting test bellows I built for the 'Vinland' series. This unit would also influence the theoretical design of the 'Icelandic/Hals' series.

'Smelt Test Bellows' - shown as part of the Icelandic furnace layout.
As it turns out, although there are some earlier postings here describing this test bellows, I never actually published any physical measurements of the unit.
I refer you to these past postings on Bellows Reconstruction : 
Rough Design with measurements

Depending on the operator, this bellows has been found to produce air volumes in the range of 700 litres per minute.
In practice it has turned out that this unit, over the course of a smelt in one of our 'standard' furnaces (about 25-30 cm ID), produces air = burn rates a bit on the low side (more typically in the 12 - 14 minutes per 1.8 kg charcoal burned). The net result is usually lower yields, into the range of 20 % return.

In comparison, the same furnace, with identical ore - but with the higher volume electric blower, produces higher quality results. (Both in terms of bloom density and yields into the 25 - 30% range.)

Sunday, July 22, 2018


After a very heavy teaching rotation over May and June, I am withdrawing from forge work over the next two months.The reason is that extensive repair and renovation work is required to the second floor deck here at Wareham. (1)

My residence building at Wareham dates (I think) to the construction of the church next door - about 1930. (My building was originally constructed as a horse/drive shed for the church goers.)
The building dimension is roughly 60 x 60 feet. It is constructed of poured concrete walls to about 8 feet, with salvaged timbers as the framing for the roof, full tree lengths as the roof joists.
These timbers are hand hewn barn beams, mostly to about 12 x 12 inches, a mix mainly pine with some hemlock. These are most certainly older than the original building construction. A number of cut nails have been found embedded over the years. (This, along with local settlement dates, suggests post 1850's to about 1900, likely towards the earlier dates.) (2)

Original deck (left) and lower cantilevered section - during dismantling
The main deck structure dates to the conversion of the original Church Shed into a residence, which was undertaken from 1987 through Fall of 1989. (I purchased the property in November 1989.)
Now, there were a *lot* of problems with the construction of this residence conversion. One factor that impacted the durability of the second floor deck was that there was no waterproof flashing applied between the deck framing and the underlaying wall beam.
I had constructed a second level deck surface, cantilevered out from the main support uprights, some point about 2000.
Additionally, I had made some attempt to brace and strengthen the original upper deck framing about a decade back. Significant water damage was obvious even then.
The massive work and cost involved in replacing the entire deck structure caused me to keep putting off the required repairs.

Showing the additional framing members added about 2008 - now also failing!
Removing the top deck planking - exposing water damage to framing.
A surprise I certainly did NOT want is what I found when I pulled off the board attaching the deck framing to the upper wall beam :

Where the original deck was attached to the wall
Close up view = 20 years of water damage
To allow for the new construction, I have laid a new 2 x 10 plank over the damage surface of the main beam seen above. I wire brushed off as much of the loose wood rot as I could, then applied an insecticide (just as a pretentative measure) first. A set of 3/8 diameter lag bolts, 6 inches long (countersunk) hold this new plank in place. This gives me at least a flat extension of the wall surface to mount the new deck framing to. Some of the damage seen is also from red squirrels who have made a home through this area. You can see the 2x4 pieces set between the existing floor joists, fitted tight to both block the squirrels and also help support the second floor (made of waffer board - not plywood!) (3)

Panorama of the construction - upright bases being mounted, deck still being demolished (July 15)
Why is this a Wareham Forge project?

Long term plans for work at Wareham include finishing replacing the (incorrect) support pillars in the workshop area. Right now the pillars that help support the entire roof structure are rail ties and hewn beams - sitting on dirt. (Not even a stone base, much less actual concrete footings! Over the years, individual posts had frost heaved up, then dropped away - to a total of as much as 6 inches of gap in one case. (Blocked up with bricks and board shims on a yearly basis!) One side of this construction was undertaken three years ago (four supports) with the aid of Kelly Probyn-Smith. (4)

The long term goal, is to finish the current rough loft level in the workshop area, into a proper studio space. Right now this area (potentially about 20 x 20 feet) has some rough plank flooring laid over the support framing. It is used only for storage of long steel, wood planks, and larger pieces of things like Viking 'A' frame tents. Current access is just via a ladder (or a narrow half sized door in the corner of the upstairs living space).

Scaled plan (draft) - new deck replacement / extension (south to top here)
Part of this overall plan is to modify the roof line, along the existing south side kitchen wall. By extending the roof slope off the residence side, this will create a short 'pocket' - allowing entrance into the loft space. A door will be added to the exterior on the east side allowing access to the outside. The current small window in the kitchen will be replaced with a narrow door - allowing direct access to the loft space from the second floor living area.
The deck itself will be extended as seen above, wrapping around 2/3 of the north wall (from the replacement of the current deck off the sliding doors). Although not illustrated on the first draft plan above, the new decking will wrap from the residence NE corner, extending back to allow a for entry into the new loft exterior door. The stairs decending from the new upper deck level will run out straight from this end / door towards the east (also not illustrated).
The new deck area will be roofed over with fiberglass panels, extending the existing roof line on the north side. This will divert water *off* the wooden structure - thus eliminating the kind of water damage caused by the original construction. An added bennifit will be also shifting the snow load down away from the deck surface (not a trivial problem with snow amounts at Wareham, compounded with the metal roofing.)

Beyond the basic increase in available studio floor space, certainly the creation of easy (and much safer!) stair and level access to the loft space is important.
Both Kelly and I have become increasingly interested in the potentials of work with ceramics - and have been slowly acquiring all the major equipment required.  (Including, at date of writing, a massive 36 inch ID electric kiln and a potter's wheel!)

So - if you had been wondering why there has not been any new artisan blacksmith work being reported...

(1) Curiously, I don't know who placed the core of this reference on Wikipedia.
Especially the part related to 'It is the home of Darrell Markewitz...' (!!)
The part in quotations was placed by myself (July 22). This is based on my memory of information given to me by Susan Thompson, who was resident in the Church at the time I moved in. (The Thompson's had undertaken the conversion of the Church building into a residence, starting something about 1985.) I had some paper documentation describing the early history of Wareham - but of course can't find that as I compose this entry.

(2) Dating via objects like nails is always quite tentative. 
- Machine cut nails are introduced about 1810, the specific style found at Wareham start about 1830.
- Availability is certainly going to shift towards the later dates (especially for a rural Ontario location).
- New types (wire nails = post 1890) also take considerable time to both become available, and importantly replace existing stockpiles of older types. 
(see 'Using Nails to Date' )

In this case, there is also the dates related to both European Settlement (post about 1850) and development lag (The first structures would have been smaller, round log. With primary effort going to clearing forest for farm land, there have been considerable delay before the expenditure of effort involved in larger, more elaborate structures.)

(3) When we purchased the property, the second floor came covered in quite horrible, recycled, shag carpet. Over the first winter, I replaced the flooring with 5/8 thick solid pine planking. This also effectively helps distribute the weight loading over that 1/2 waffer board used as the sub-flooring!

(4) This proved a massive job! 
First, about 1/3 of the workshop area needed to be cleared out. 
Next, the main horizontal beams had to be jacked up, taking all the load off each of the existing 'supports'

Friday, July 20, 2018

Summer Solstice Iron Smelt : REMAINS

The objective of the regular early summer experiment was further investigation of the 'Slag Pit' style furnace - tentatively described as 'Celtic Iron Age'.

Refer back to an earlier postings for the :
build / experiment outline
conduct of the smelt itself

The upper furnace was a re-use of my 'production build' from May 2012. It not only has run through several uses, it had been sitting outside (semi-protected) for 6 years (!). When I attempted to lift the furnace body off, the metal outer can pulled free - and the interior walls completely broke apart. (1)
The details here start after the broken furnace wall pieces had been cleared away.

Note on the images :
It was blindingly bright the morning I excavated and recorded. Many of the images suffer from exposure problems because of this. For that reason, relative brightness and contrast has been altered via Photoshop on many.
There has been an attempt to mark the location of the tuyere on several (use of the scale, or via an added arrow).

Base of Furnace - broken walls removed
In the (admittedly poor) image above, you can see the shell of fused wall and slag remaining along the 'hot spot' at the tuyere (far left - indicated by scale). In this image, there is still a lot of loose, small fragments from the broken walls covering the top of the slag bowl. You can see that this bowl is sitting higher to the tuyere side, not extending completely over to the side furthest from the 'heat zone'. 

Cleaned furnace base, showing bloom and it's position

The next image shows the furnace base, with all the loose wall pieces removed and as much as possible of the fine debris cleared off the slag bowl. The bloom is shown on its side (so top side is towards the bottom of the image). Tuyere marked with an arrow. Matching up the X (centre of bloom - bottom surface) and Y (extended 'tail') indicates the location of the bloom as it formed. The slightly scalloped edge of the top left of the bloom (so closest to tuyere) suggests that into the end of the smelt, the air blast effected the deposit of iron and shape of the bloom. Slightly oxidizing to the front, the heat zone pushed further back moving higher up from base level.

Slag block as lifted clear of the pit
Close up of the slag block - X indicates bloom / arrow the tuyere
The next step was to pull the slag block out of the pit. 
The way the heat had eventually effected the clay cap, and the seeping of hot slag into the pit was clear. The slag had formed into a roughly conical shape, wider and deeper directly below the tuyere 'hot spot'. Individual 'icicles' of slag became more distinct towards the bottom. In fact these extended down even further into the pit area, but broke clear when the slag mass was lifted. The main solid slag mass extended about 15 cm below ground / furnace base level.
There was also a clear colour and consistency shift to the slag as it moved further down away from base level. The upper bowl was dark and solid, clearly the most iron rich. Slag excavated from the lower pit tended to be a lighter colour (tinges of green) and contain more bubbles.

Fragments of the clay cap
From the rear area, about ground level, it was possible to pull out some larger fragments remaining of the initial clay cap (covering and separating the vegetation packing the pit). It was easy to distinguish the upper (burned black) and lower (cleaner) surfaces. The lower surfaces had clear impressions of the plant stems and leaves the soft clay had been packed against. 
Towards the front, the clay had ether been melted away, or was completely enveloped by the slag.

'Icicles' of slag, running down from the upper bowl
Carbonized stem fragments, about bottom of slag block (1/4 inch grid)
Individual slag flows had penetrated further down into the pit. These proved not firmly enough attached, or too physically weak, so broke free as the upper mass was lifted clear. As individual runnels of slag were exposed, some were found to contain carbonized stem pieces. (2) As well, individual stem lengths had been transformed into short charcoal sticks. At this depth (15 cm +) there were no remains of the leaves found.

Moving towards the bottom of the pit, slag was found to be fragmentary, lighter and containing much more bubbles. Although clearly heat effected (surface carbonization), individual leaves remained. These were found to be damp and still pliable. 
There was no slag penetration below 30 cm. (Although partially blocked with stones left in place, the deepest part of the pit extended to 35 cm below ground level.)

(1) My best guess here is that moisture had penetrated the baked and partially sintered clay / sand construction. Even despite the wood splint pre-heat, water expanding into steam resulted in the structure pretty much fragmenting. 
There may be some indication here why the Norse would have built structures over furnaces (consider the 'Furnace Hut' at L'Anse aux Meadows). Not for the protection of the *workers* - but for the protection of the furnaces themselves.

(2) Of interest here is the potential preservation of vegetable packing materials fully inside glassy slag. At Heltborg in 2008, one of the interesting presentations was on research being undertaken on the organic materials preserved in ancient Danish slag blocks. The glass slag is virtually indestructible. Vegetation trapped inside the slag can produce information on environment / dating / crop types, even time of year for the smelt.

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

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