Saturday, June 28, 2014

Canada Day DEMO...


I will be undertaking a 'Pioneer Blacksmith' demonstration as part of the Canada Day events at the Grimsby Museum.

Museum open on Canada Day : 10:00 a.m. to 3:00 p.m.
Demonstration Period :  11 am to 2 pm (likely extended)

Friday, June 27, 2014

Furnace Types?

(from Alan)

Have you ever used a slag-pit type furnace?  I was trying to wrap my head around one of those the other day, when I read an article saying the pit was filled with tamped dry straw which allowed the slag to settle into the pit slowly, leaving the bloom free to grow and extract. 

One of the problem those of us looking at historical bloomery furnaces run into is that there is no clear typography established to describe various furnace designs.  As the primary archaeological remains are almost always at best a slag bowl in place inside the vary base of some enclosing walls, much of what is described is based only on slag. Bad news for us attempting to actually * make * iron, knowing about only the base construction hardly gives you enough to build a correctly * working * furnace.
Most of the current technical knowledge of effective bloomery iron furnaces comes from the pioneering work of Lee Sauder & Skip Williams, along with an additional decade of trial and errors by the 'Early Iron Group' (via Lee's 'Smeltfest' workshops).

(Feel free to discount the following, but this is more or less how I see it. Note that this is for European historic designs only. I have never worked with a Japanese Tatara system, and only once with one of the African based furnaces)

The basic European model is a Slag Taping furnace. These furnaces are set on ground level.
This may be set up to allow for :
'Incontinence' (self taping)
Tap Arch (periodic larger taps via an opening in the base)
Continuous Taping (ongoing via a slot cut upwards from the base)

In Denmark, many of the bloomery furnaces I saw in use were what they described as  Slag Room furnaces. The furnace is set at ground level, but with the tuyere elevated to leave extra room for a chamber for slag to collect into.
Michael Nissen's Furnace - Heltborg, 2008
Our 'Shaft on a Plinth' is a variation of that basic design.
(Near as I can see, the Culduthel furnaces are this layout.)

Ancient Danish and also some Anglo Saxon furnaces are full Slag Pit furnaces. There the furnace is at ground level, but underneath is dug a pit of roughly furnace diameter for the slag to drain into.
This pit is filled with some kind of vegetation -  * the pieces set on end like a bundle of drinking straws * (may be a sheaf of grass or small twigs). Initially un-burned charcoal (below tuyere level) rests on the tops of the supporting vegetation. As the slag forms, it can drip down between the individual pieces. Eventually the heat chars and burns away the tops of the supports, and so the whole slag bowl can sag downwards as it enlarges.

We ran two tests of a full Anglo Saxon type Slag Pit furnace here at Wareham:

This is an image of an 'Iron Age' (c BC/AD) slag mass from a Danish Slag Pit furnace, the mass is about the size of a bushel basket, and is upside down. (from a location near the base of the Jutland, Denmark)

Thursday, June 19, 2014

Pictish Late Iron Age Smelt - Overview

This will be a fast overview, mainly as a photo essay, on the bloomery iron smelt carried out at Wareham on June 14, 2014.

The prototype is Culduthel, Scotland, circa 200 - 400 AD.
The furnace is a 'slag room' type, with a clay shaft built on a withy frame, over a stone base. The general details of the layout were similar to other Late Iron Age / Viking Age furnaces built in the past. The material used was a 50 / 50 mix of dry clay and course sand.
(See the earlier post : Scottish Dark Ages Iron Smelt )

This smelt was a test / training for the 'Turf to Tools' project being undertaken at the Scottish Sculpture Workshop over August 9 - 25, 2014.

Clay shaft being built up on a wicker frame, over a stone base chamber.
After drying fire - extensive cracking of the shaft (extraction point to right)
Equipment set up, at pre-heat phase.

Adding the DD-SSW1 analog
Bloom mass at initial extraction. Bottom pull was intended, but top extraction was required.
After two initial compaction heats, an attempt to cut the bloom.
Final Bloom : 5.2 kg (from 28.3 kg dry ore = 18% yield)
 The next day, the bloom was re-heated and compacted using the hydraulic press. After cutting to quarters, the interior surface was spark tested. The observation suggests roughly .6 -.7 carbon content, a good blade making material. (!)

The following will be of more interest to the archaeologicallly inclined:

The overall remains from the smelt around the furnace.
Broken pieces of the furnace, clearly showing the imprint of the wicker interior frame.
Furnace opened along the major cracks, showing the slag bowl in place below the tuyere entrance.
Main slag bowl removed as two pieces. The tuyere was to the left.
Cleaned surface of the rock base. Tuyere was to the top.

There will be a fuller report to come on making a comparison between the results here, and the remains seen in the archaeology from Culduthel.

Some General Conclusions:
  • Some modifications to the layout and construction of the furnace may be necessary to :
  1. avoid cracking
  2. conform more closely to the slag pattern at Culduthel
  • The analog used proved quite successful, even if the yield was a bit low.
  • The general progress of the smelt followed the expected pattern.
  • A better system needs to be established for re-heating the bloom for consollodation.
With thanks to the working team:
Kelly, Ron, Heather, Rodger, Neil, Richard.

Tuesday, June 17, 2014

Dutch Iron Production in the Middle Ages

This is a great video available on YouTube, featuring long time experimenter, skilled blacksmith and artist Thijs van de Manakker.

The film runs roughly 25 minutes (!) with the historic framework set at c 900 AD.

Although the explanations are a bit simplistic, the activities shown are complete. Paying attention to the entire sequence will give you a lot of insight on furnace construction especially.

Thijs pioneered the use of a twin tuyere system, using two drum bellows. The filmed sequences can give a good estimation of air volumes. One nice addition is the second step, showing the specialized forge set up he uses for the bloom to bar phase.

As a fellow iron maker, I would have liked to have heard some details on ore quantities, addition rates, and yields. But honestly, this kind of technical information is not the intention of the filming

There are a lot of background sequences shot at the Bergherbos Montferland Medieval Heritage site in the Netherlands. The site - and the people there - look just wonderful. (Only a few small inconsistencies caught my eye.)
One thing that did concern me was the complete lack of any safety glasses being used. (Although is is certainly historically accurate, it is just plain not very smart around an iron furnace!)

(I was having trouble accessing the direct 'plug and play' link off YouTube. Hopefully one of these two links will take you direct to the full video...)

The film shows some excellent re-creation work by Thijs. It will certainly be of interest to those involved in living history for the Early Medieval / Viking Age period. Most especially worth the viewing for any considering / working towards historic type bloomery iron smelting furnaces.

(thanks to Vandy for sending the link)

Thursday, June 12, 2014

Scottish 'Dark Ages' - Iron Smelt

For those of you who have following the fine details, I have been invited to lead a special project at the Scottish Sculpture Workshop this August.
SSW is about half way between Aberdeen and Inverness, in the small village of Lumsden (Lumsden, Huntly, Aberdeenshire AB54 4JN, UK)

Turf to Tools is a two week long collaboration project, running from August 9 - 25. The underlaying intent is to use locally available materials to smelt iron using historic methods, then take the iron created to produce a replica of a specific object - also based on a specific local historic source.

The target object is an axe, the one seen on the 'Rhynie Man' picture stone:
The stone is from nearby Rhynie, and is dated to roughly 700 AD (what was a major political centre at that time). The date makes it clearly 'Pictish' (post Roman and pre Norse).

What is likely the best reference for the iron smelting process is from the archaeological site of Culduthel, which is located at the SW corner of Inverness (about 125 km roughly NW). This site is a longer term occupation, but the main iron smelting activities appear to bracket 200 - 400 AD. There were multiple bloomery furnaces uncovered there.
I have not been able to get a lot of details on the furnace archaeology, but some hints from the partial report and summary I do have suggest:

1) Stone chamber at base - a 'slag room' system
2) Clay upper furnace (no specifics on composition)
3) Build over a wicker framework
4) About 30 - 35 cm interior base diameter
5) Most probable bottom extraction

As the size and general layout (and honestly, historic period) does match my main experimental practice, most of the working system prototype is like that earlier work:

For this prototype smelt :

1) Use of 'standard' ceramic tuyere
2) Electric blower for air

I was able to scrounge a wicker laundry basket to use for the interior form on the build. This is tapered, which is an advantage. This form is 60 cm tall, 25 at the top diameter, 38 at the bottom.
Since there is no specific reference made to cobb or organics added to the upper clay construction at Culduthel, the mix will be roughly 50 / 50 clay and sand.

The charcoal I have on hand is Oak. Currently I don't know exactly what species will be available at SSW, but (more or less) this is not considered a major concern at the test phase.

One of the larger unknowns is ore.
I had made an earlier general commentary on the local 'Macaulyite' ore :

Some considerations on Iron Ore for 'Turf to Tools'

This material is specific to the Lumsden / Rhynie area. (Unfortunately, the Culduthel report does not go into any specifics about any ore that might have been recovered at the site.) 

One of the DARC team (our in house geologist Marcus), has suggested the following for the active chemistry of Macaulyite:

Fe2O3 = 78 % 

SiO2 = 10.5 %

Al2O3 = 4 %

H2O = 7 %

With a weight of Fe of 60%, this should be a nicely yielding ore. The combined silica and alumina are a bit high however. I was sent a small sample of the available Macaulyite, and the particle size is about the same as rice grains - which is a bit on the small size. 

I have made up a version of our dependable 'DARC Dirt' analog, with potter's oxide as the primary component and additions to match at least roughly the chemistry above. 

'Spanish Red' oxide = 25 kg

Alumina = .5 kg

Silica = 1.25 kg

Wheat Flour = 2.5 kg

This is dry weight, there is always considerable water weight remaining (which we will calculate via a small sample later). 


Expect several more postings detailing furnace build, iron smelt and the bloom to bar phase!

Note : The smelt itself will take place at Wareham on Saturday June 14, starting about 9 AM, with extraction expected some time between 4 - 6 PM. As with past experimental smelts, this is a 'semi open' event : The truly interested can attend, but please (!) get in contact with me via e-mail if you want to come up. Do expect my major focus to be on this prototype smelt, a training and rehearsal for the SSW project.

Thursday, June 05, 2014

DARC at UCV - this weekend!

DARC at Upper Canada Village Medieval Festival

Saturday June 7
Sunday June 8
Monday June 9 (Education Day)

Morrisburg, Ontario

The Dark Ages Re-Creation Company will be mounting a presentation of daily life / life of the artisan during the Viking Age as part of the larger Medieval Festival at Upper Canada Village this weekend.

The core of the DARC living history presentation will be two complete 'camp' set ups, illustrating aspects of daily life, including domestic tasks centred on food preparation. Additionally, there will be four primary working artisan demonstrations ongoing :
Textiles (spinning / weaving / related fibre arts)
Glass Bead Making
Green Woodworking (spring pole lathe)

Images above from DARC's 2013 presentation

Cross Posted from the DARC Blog

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

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