'65 for 65' - Samhain Iron Smelt
October 31, 2020

Smelt Team:
Neil Peterson, Rey Cogswell, Richard Schwitzer (compaction) of DARC
Bram Porter
Smelt Master : Darrell Markewitz

I had been casting around for some direction to head with the long set of individual iron smelting experiments, now after the better part of 20 years of undertaking.  When my long time collaborator and smelting partner Neil Peterson was up to Wareham October 22 (for a day rendering bloom pieces into useful working bars), he asked what the plan for the normal Samhain Smelt was.

The last experimental smelt was the 'Bones' test in June. Although there could be a continuation there, truthfully I don't feel there is much insight to be gained that would be worth the investment in materials, time and effort. I had started some background on early Irish ‘bowl’ furnaces, but not enough at this point to realistically frame a working experimental series based on this.

We considered the state of the current test furnace, the stone block, built for a second Icelandic research project over 2019. ( 1 ) This furnace had been fired four times at that point, and had suffered some structural damage on its last use (course over Thanksgiving).  Given the shift to colder late fall temperatures (below freezing at night, mid single digits daytime) and the general lack of a clear direction forward, I decided to repair this furnace for one more use, rather than attempt a new full build.


Condition of the stone block after Oct 11 smelt.
The red line is where the original lintel stone (above the extraction arch) had broken out.


Interior erosion from the Oct. 13 smelt.
When the tuyere was first set, it extended 5 cm proud of the furnace wall - roughly the red line shown.
I was turning 65 just days after that already long scheduled Samhain Iron Smelt, set for Saturday 31 October.
With tongue in cheek, Neil said : " 65 in 65. You could smelt 65 kg of ore. "

Now, the largest volume smelts I personally have ever done have been with 45 kg of ore ( Smeltfest 2006 ). These also resulted in some of the largest blooms, into the range of plus 20 kg. Attempting 65 kg could potentially increase everything by 40 %, importantly the amount of charcoal consumed and raw working time required ( 2 ). Bloom yield also can increase steeply with larger ore amounts. I was not really sure the furnace on hand would contain what (hopefully) would be such a massive bloom!

I have commented a number of times about the problem we have here at Wareham, perched as we are at the top edge of the Niagara Escarpment. This is basically a block of solid limestone, in the range of 100 meters thick, that runs about 750 km from north to south, and almost that wide east to west. ( see blog post ) Although there is certainly iron traces in the well water at home, the physical geography just does not permit formation of any iron ores.
For that reason, my own experience has lead having had to work with a great number of both types and qualities of ore,  perhaps more than any other experimental team ( 3 ) :
The standard here for some time has been our own ‘bog ore analog’, composed primarily of red iron oxide powder (Fe2O3). This material was developed originally in an attempt to copy the chemistry and physical structure of the primary bog iron ore found at L’Anse aux Meadows, Newfoundland, as part of the ‘Vinland’ experimental series.

Just recently, the metal bands on wooden barrel slack tub failed. One of the 'mystic' things at the Wareham Forge is that this tub had never been emptied since I set up the forge here back in 1990. (The first filling included some water gathered from the point where Black Duck Brook mixes with the ocean, just downstream from the Smelter Hut at L'Anse aux Meadows.) In the process of replacing the bands, some of 30 years of accumulated iron forge scale was collected. This material, 2.5 kg, had been added to the analog mix being made in preparation for Saturday's smelt. Additionally, recent forge scale, magnetically gathered after working sessions, was included. The scale portions would be largely Fe3O4, but were certain to contain a certain amount of silica (in the form of dirt). This mix would be considered to be DD1A3 :
This all was mechanically mixed, then water added to make a paste, that spread on trays. Drying this mixture proved a problem, with the cool and wet weather. The trays were set under heat lamps for a week to dry them.
A 100 gm sample was set aside. This was (later) baked at 230 C (450 F) for 15 minutes to drive off the remaining water. The result was a loss of 4 gm, so ore amounts could be adjusted to reflect this 4% amount. (Note of this is sometimes made, but normally ore totals are not adjusted, but recorded as individually weighed out before adding to the furnace.)

Against Neil’s (off handed) suggestion, it occurred to me that I did have amounts of most of the other ore types we have worked with actually available. ‘Duplicating History’  suggested starting with limonite (pretty much were we originally started, and a tribute to Lee Sauder and Skip Williams). The only major type from the list above that was missing was industrial taconite which was the next ore body we worked with.  Next was hematite, available easily here in Ontario at that point as sand blasting grit. A main type would be a batch of DD1A3 analog.  I also had a quantity of small quantity of gromps ( 4 ). Last additions would be more of the previously roasted limonite, enough on hand to complete a possible total to 65 kg.


Initial set up of the furnace (layout drawing)

Past use of this specific furnace has shown it will accept alternating 2 and 3 kg charges at the end (this against standard 1.8 kg charcoal amounts, burn rate averaging 14 minutes.) The stone mass has been found to take significantly longer to come up to working temperature (in the past about 2 + hours). With our normal roughly 30 kg ore amounts, the elapsed time of the main sequence has been in the range of 5 hours. That all suggests an attempt at a 65 kg smelt would add about another 3 - 3 1/2 hours to the main smelt sequence, suggesting a total experimental time (first pre-heat to final extraction) of 12 1/2 hours.  Because of this expected long duration, I was out starting the initial preheat at just after 7 AM, before dawn that morning!


Interior patching around the tuyere. New clay shows as the light grey material.


Exterior repairs, during initial pre-heat.
New lintel slab and additions (compare with image from 10/14 seen above).
You can see the height of the charcoal fine / ash layer base (equal to the lower flat stones).

The first (ungraded) charcoal was added at 9:35, making the pre-heat phase using split spruce lumber pieces a full 2 hours.  A first full bucket was added, which filled the bottom to just about tuyere level, this was allowed to fully ignite off the remaining coals of the wood pre-heat. Then followed up with a further 4 buckets to completely fill the furnace. The combination of the large pieces of charcoal, and the extremely jagged stone interior, served to cause the initial charcoal charges to hang up in the interior. The charcoal was lightly probed several times over this initial ignition phase so the fuel would correctly settle.

One thing that had become apparent over the last several smelts is that the sliding gate used to control the volume of the blast had started to seriously bleed air. (For the number 86 smelt, the gate had been set at ’1200 LpM’ - and still the burn rate averaged 14 minutes / bucket). Working as much by blast sound as anything else, this time the gate was set to the marked ‘900 LPM’, but taped over to stop any air leakage. ( 6 ) The effect of this repair was clearly seen, with the burn rates over this smelt averaging a very consistent 12 - 13 minutes per bucket of 1.85 kg oak charcoal.

In keeping with our current ‘best practice’, a total of 3 kg (6.5 lbs) iron rich tap slag would be added as initial ‘bowl forming’ charges. ( 5 ) It was expected that between the extra silica in the limonite, expected erosion of the clay added to the interior of the furnace to repair it, that there would be a fair amount of slag generated and requiring taping over the sequence.


‘Lexington Brown’ Limonite - roasted and broken into ‘rice too peanut’ size

The first series of ore charges was a total of 6.5 kg of limonite. The ore on hand, does tend to be on the lower iron content side compared to the other ore types. This had certainly was the case in past uses of the materials I had  personally gathered, mainly due to lack of experience spotting the most suitable rocks. This higher slica content (hence slag formation) was expected to be balanced with the hematite, which if anything tends to be too ‘dry’ (lacking in silica for slag formation). Individual charges started (as usual) at 1 kg per standard bucket, increasing to 1.5 kg each

Not too surprisingly, about the time the first set of limonite charges were complete, observation of the furnace suggested the initial slag level was sitting a bit to high, and the developing bowl was probed to both drain it slightly, and to get the hot slag to settle lower into the furnace.


Hematite Grit being added

The next series of charges was the granular hematite. Again a total of 6.5 kg was added. Now at 1.5 kg ore per bucket, four charges were all it took.


‘Other types’ - Industrial Taconite / DD2 / LAM Primary Bog Ore

To round out the ‘history of smelting’, samples of the other ores I had worked with were added, before the start of the DD1 analog. This included a pellet of industrial taconite (from Defasco, Hamilton). A piece of DD2 analog, which is primarily composed of black Fe3O4 oxide powder. Finally a small piece of primary bog iron ore, gathered from Black Duck Brook at L’Anse aux Meadows, just upstream from the Vinland site.

The bulk of the ore added was the DDA3 analog as described. By the point in the smelt when this started (roughly 2:45 into the main sequence) individual charges had increased to 2 kg per bucket. It was found the burn rate stayed quite consistent with altering 2 and 3 kg charges. A total of 31.5 kg of analog would be added  (which actually works out to 69 lbs).
To round out our ‘history’ the next charges were addition of smaller pieces of collected groups. Here again the total was 6.5 kg. Due to the high metallic iron content, the size of individual charges was reduced to 1.5 kg.

Overall Smelt Data


Neil tapping slag in the later stages of the smelt

By this point it was clear that the slag bowl was sitting higher than ideal. The stones blocking the tapping arch had been pulled free, and a number of times a hole was poked into the upper part of the slag bowl draining the slag level to ensure the air blast would remain clear. The charcoal fines packing was scrapped clear, with an attempt made to let the hot slag run into the additional 10 cm space this had taken. The hope was that this would allow the slag bowl to settle, creating more room for what was clearly a very large bloom to accumulate even further.

After the main set of differing ore types had been added, the total was 45 kg (not including the gromps). As the furnace was still operating well, and there was still plenty of charcoal  on hand, it was decided to continue towards a total addition equal to 65 kg. There was still a good quality of roasted limonite, partially broken, on hand. A further total of 13.5 kg, mainly as larger 3 kg per bucket charges was added.
With what has also become our standard method, a further two buckets of charcoal were added to cover the last ore charges, to ensure any reduced iron would be able to settle and adhere to the bloom.


Starting to dismantle the furnace

It was obvious that this would be an extremely large bloom, especially compared to our work over the last decade, where 3 - 5 kg were the normal goal ( 7 ). It was clear that there would be no way to get the huge bloom / slag mass out through the bottom opening available. It was also felt there was no reason to retain the furnace itself, in fact there might actually be something to be learned by dismantling it, block by block.  After the charcoal level had dropped down about 25 cm, individual layers of the stone blocks were pulled off. These were dropped in a metal container, partially for safety, but also to simulate what would be likely to happen in historic process. ( 8 ). This process of allowing the burning charcoal to drop below a line of stones before pulling a row off continued, until the level just above tuyere height was reached.


Furnace stack as fully dismantled

With the last charcoal barely covering the upper bloom, an attempt was made to compress in place, using the log ‘thumper’. Despite a good attempt, it was clear than not a lot of effect was being made to such a large mass of iron - even at this, it’s hottest state.


Starting to pull the bloom mass clear

It had already been decided that the only practical way to manage a bloom of our imagined size would be to pull it clear of a basically broken furnace, then forward down on to the lower level ground. Although space was expected to be extremely tight, a thick disk of wood had been placed on the ground to act as a compression surface. The strikers would have to work on their knees for anything approaching correct or effective hammering. A thick plank of wood was placed edge up on the ground as a short fence to protect them from the intense heat (and to stop fractured off pieces bouncing into their legs). As I had assumed the honours of doing the actual extraction, I would continue attempting to control the position of the mass holding with tongs. Neil, Bram and Richard took the available sledge hammers and donned gauntlets, aprons and face shields.

extracted samhain

Hammer compacting the hot bloom

The second image above, shot from available light, is quite dramatic - if obscured in detail. It does point out something quite important - it was full dark by the time the bloom was extracted. An attempt was made to rotate the mass so at least each of the potential 6 surfaces had a turn at being stuck while uppermost. It would become clear that there was not a lot of additional slag clinging to the outer surfaces after this cycle of hammering (roughly 9 - 12 strokes between the three workers to each face).


Too Big! Attempting to fit the bloom under the press working plates

It was quickly decided that any attempt to section this sill huge mass would best be carried out on the hydraulic press, back in the main workshop. Neil undertook the daunting task of ‘frog marching’ with the still orange hot bloom in tongs, while I raced in front to get the equipment ready. Even with the 30 ton press, only minimal compaction proved possible. An attempt to use the cutting die resulted in only scoring the top and bottom surfaces at best through to outer quarter distances.

As we usually do, the team made their guesses on the final bloom weight. Perhaps with more experience (?) my own estimate was 15 kg. As a side note on this smelt, we finished up our final 'closing ritual' and major equipment packing up at roughly 8 PM, making the total working time 12 3/4 hours.


Weight of the finished bloom (next day)

The next day, still slightly warm mass was placed on a bathroom scale. You can see the result above, 35 lbs / 15.9 kg.  The top surface is uppermost here, the (very) rough relative angle and position of the tuyere is indicated by the arrow. You can see how there has been a depression dug out of the one end of that top surface, caused by the slag bowl forming a bit too high, and the raw size of the mass itself. This placed the top surface too close to the air blast, which has eaten it away. There is a clear lifted edge on the side furthest from the tuyere, again a result of so much metal piling up in the furnace interior. The initial interior diameter at tuyere level was roughly 25 cm, and you can see that the bloom measures about 22 cm front to back.

The yield result is ‘only’ 24.5 %, 15.9 kg bloom from 65 kg ore. This is intact a bit lower than I expected. Usually high volume ore smelts quickly ‘slam on the mass’ and result in significantly higher yield percentages. To be fair, past uses of the same poorer quality Virginia limonite have only produced yields in the 10 - 15% range, and this ore comprised almost 30% of the total used in this smelt. There also was a higher amount of forge floor sweepings than normally used in the batch of DD1 analog prepared.
Even so, a roughly 25 % return is certainly quite acceptable. The raw mass of the bloom is also one of the largest I have ever made.

Any image containing me ( * ) is by Kelly Probyn-Smith

( 1 ) Some of the background research I did over January to August 2019 was used in the preparation of a lecture styled presentation for the ‘virtual’ Woodford Furnace Festival, on August 23, 2020. ‘West Viking - Iron Smelting’ is available for view on YouTube 

( 2 ) This not strictly true. At the later end of a smelt sequence, charges are typically large, 1 : 1 with charcoal, or even more. One problem right now is that with COVID, the normally used 'Maple Leaf' brand via Home Hardware is completely out of stock - and back ordered to at least Spring 2021. Recently Canadian Tire was able to secure a bulk order of Royal Oak out of the USA. Neil grabbed a large quantity, but stores quickly ran through that stock. One thing we noticed is that although the bags are the same size, the amount contained has shrunk, from the previous 20 lbs (9 kg) to now 8 kg (17.6 lbs).

( 3 ) These totals may not add up to the full 86 smelts undertaken by me personally to October 2020. In a number of cases, combinations of ore types were used on a single smelt (recorded as .5 each).
Data about the various ores (iron / silica contents) can be found here
( 4 ) Gromps are the slag and iron fragments that flake off an extracted bloom during it’s initial compaction. These typically small pieces are magnetically gathered.

( 5 ) This a method demonstrated by Michael Nissen during the 2016 ARTEfakty event in Poland. Adding a quantity of iron rich tap slag as the first charges quickly establishes a working slag bowl, allowing the first reduced iron ore to go straight to depositing a metallic bloom (thus improving yield).

( 6 ) When this control system had been originally introduced (April 2008), coupled with the high efficiency US Navy surplus blower just acquired with help from Lee Sauder.
Using a small wind speed gauge, in line measurements were made and volumes calculated. Various volumes were marked on the sliding plate, roughly corresponding to increments of 100 LpM. It is these numbers seen recorded on the smelt data sets after that date.
( 7 ) The objectives have been normally to test specific furnace designs, mostly based on historic prototypes or variation in methods. For that reason, most typically ore amounts have been kept to the 25 to 30 kg range. Practically, if you can make a 3 kg bloom, it is just more ore and charcoal (time) required to make a larger bloom.

( 8 ) These hot stones certainly would have been pulled off and dumped well out of the way of workers - for the same reason we were collecting them together. Individual stones had quite differing surface effects from the variation on temperature they were exposed to, based on their location within the body of the furnace. Previous measurements had shown that near the top of the furnace, temperatures range about 800 C. Moving lower, as much as 1300 C was certainly possible.

unless otherwise credited - Text and photography © Darrell Markewitz