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 : 
ONE / TWO / THREE / FOUR
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

July & August = DECK CONSTRUCTION

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.

Sunday, July 15, 2018

Summer Solstice Iron Smelt : RESULTS

As in past years, there was a late spring / early summer iron smelt at Wareham. The date for this June 23 - 'the Saturday closest to Summer Solstice'.
The objective of this experiment was further investigation of the 'Slag Pit' style furnace - tentatively described as 'Celtic Iron Age'.

Refer back to an earlier posting for the build / experiment outline.

Near the end of the main sequence - Neil Peterson probing to determine bloom size.
Hammering on the bloom in place, using the 'Thumper'. (a)
Top Extraction of the hot bloom. (a)
ORE : 28.2 kg
DD 2B = 22.68 kg red iron oxide + 2.5 kg whole wheat flour + 2.75 kg forge scale
  / water to mix, then dried (typically about 10% remains)
CHARCOAL : roughly 62 kg
  Mix of Maple (2/3) and Oak (1/3)
AIR : via electric blower = estimated 900 LpM, increased to 1000 LpM at 4 hours
TIME : about 2 hours from start pre-heat to fill / touching off volitiles
  about 5 1/2 hours for the main sequence (to start burn down)

Initial charges : Iron rich slag (2 @ 1 kg) + Gromp fragments (2 x 1 kg)

Burn Rate : Average of 12 minutes (very consistent)
  First 7 ore additions at 1 kg each
  Next 3 additions at 1.5 kg each
  Last 7 additions at 2 kg each
  Final addition at 2.7 kg (remainder on hand)

Final Bloom, shown upside down, tuyere side to right. (b)

BLOOM : 6.1 kg
YIELD : 22 %
QUALITY : not cut at this point, but hammer feel suggests quite dense.

TEAM : Neil Peterson / Gus Gissing / Margaret Gissing /  Ben Van Eis

Next : Excavation of the slag block...

Image Credits :
a) Kelly Probyn-Smith
b) 'Gus' Gissing
 

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

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