Friday, March 27, 2015

Viking Age Air at Early Iron 4

 Early Iron 4 - in April!    
 From: Darrell Markewitz
Darrell Markewitz will investigate air supply into a Viking Age furnace.
I had not realized how cut up the original description had gotten - and this was the point of a bulk mailing that had been sent out earlier this week

This is from the longer text version:
Darrell's first attempt at a bloomery furnace was at a research session for Parks Canada in an attempt to re-create the first iron smelt in North America by the Norse (about 1000 AD). Since then, he has concentrated on re-discovering lost Northern European techniques from the Late Iron Age, using the process of experimental archaeology. Darrell was a team leader for all of the previous Early Iron symposiums, as well as another core member of the Smeltfest research workshops. He has taught historical iron smelting both in Canada and the USA, as well as taking part in research projects in Denmark and Scotland.

Darrell will be undertaking an experimental archaeology project which also will provide a more basic level furnace construction and operation sequence for less experienced bloomery iron makers. The furnace will be a 'Norse short shaft' type, to be built over the early afternoon on Friday. The smelt on Saturday will employ a 'bog ore analog' and the experiment will centre on using multiple double chamber bellows linked to a bladder as a possible method to produce high air volumes. Participants actively sought!
Friday afternoon - build
All day Saturday - smelt

The core here is my ongoing research into possible VA iron smelting techniques. Archaeology actually only gives us broken remains of only the last step in a complex multi-step process, and usually heavily eroded at that. Modern re-constructions using various variations on Norse type twin chamber bellows most commonly produce smaller, lacy blooms. The few artifact blooms surviving are larger and more dense, more like the blooms made using much higher air volumes.
My question is 'how do you get high air volume from small capacity bellows?' One at least theoretical possibility is linking a number of smaller 'blacksmith's' bellows via a leather bladder (animal skin). Placing a board and weight on top could serve to modify delivered air pressure (another important factor effecting smelting furnace dynamics). This system may also suggest something about the social dynamic around small scale iron production in the Viking Age.

I do hope some of the readers in the NE region of the USA might consider Early Iron 4.

Sunday, March 22, 2015

EARLY IRON 4 - one page

 Early Iron is a gathering of individuals with a keen interest in the small-scale smelting of iron from ore.

Even after almost two decades of many trials and frequent failures, many puzzles of exactly how historic direct process bloomery furnaces work still remain.Early Iron 4 will once again pull together those who continue to experiment.
Lee Sauder, certainly the most experienced and best known worker with direct process bloomery furnaces in North America, will build and fire an experimental furnace based on the medieval Spanish Catalan type, assisted by 'Early Iron' instigator Mike McCarthy.
Jesus Hernandez, one of the top bladesmiths making and using bloomery iron in the USA, will bring his understanding of the Catalan as well as share his extensive experience with 'bloom to blade'.
Darrell Markewitz will investigate air supply into a Viking Age furnace. Early Iron 4 will not just allow participants to observe, participate and learn. It represents a chance to pull together individuals interested in all aspects of the riddle of Early Iron, face to face - to the enrichment of us all.  
Compacting a freshly extracted bloom 
For more details on workshop packages and schedule visit the Early Iron 4 website.
We are excited to be sharing the Ashokan Campus with the Northeast Blacksmiths Association for their Spring Hammer-In. Learn more about their program at Northeast Blacksmiths Association
Mike McCarthy guides a working team
Lee Sauder adding charcoal at Early Iron 2.

Nami ni Chidori Nagamaki by Jesus Hernandez
Historic illustration of the Catalan furnace
New to iron smelting and blacksmithing or just curious? A special area and time will be reserved for hands-on practice of fire-tending and basic forging skills. Tools, equipment, and coal are provided and available for purchase on site. Student discounts and parent/child scholarships are available. For more information, go to the Early Iron website.

Bloomery iron ring
by Mike McCarthy.

For more information about the Ashokan Center facility and programs  visit:  Ashokan
Future Blacksmithing Events at The Ashokan Center:
  • New England Bladesmith Guild Annual Seminar September 18-20, 2015
  • Northest Blacksmiths Association Fall Hammer-In October 2-4, 2015
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Saturday, March 21, 2015

Early Medieval 'Twin with Bar' Bellows?

On 09/03/15 1:21 PM, Brandon wrote:
I was wondering if you could help me with a bellows related question, namely proportions. The style I'm trying to make are seen in medieval artwork, side by side connected by a lever and rope. I know how long I need them to fit my setup (36" overall) but the width and height when inflated is the main issue.
I have never made that particular style. I have seen a number of medieval depictions.
On a guess from the rough period of the historical illustrations, these are most like (??) to date to time when charcoal was still the primary fuel. 

Typical of many Medieval illustrations, you can see the artist did not draw a working system!
The exact mechanics of how these work is hazy. The illustrations (sometimes) show a bar or rope off one side of the cross bar linking the pair of individual chambers. 
To get this to work there would also have to be a counter weight on each of the bellows top plates. 

Pull down on the handle lifts the opposite chamber to fill it, on the near chamber the weight on the top plate is forcing it closed and exhausting.

 Letting go the handle reverses the blast / fill process. I would think that the weights might have to be considerable to get this all to work effectively. The weight on the far chamber would have to not only close that one, but also be enough to provide the lift for the near chamber. Arm power would be every second 'blast', and the pressure of the blast would be fixed only by the weight size. It seems to me it might be hard to get an even constant blast between the two chambers (??) Maybe if the power was supplied by a solid stick, you could be providing arm power on the exhaust for both sides (???)

The Viking Age 'double chamber' side also alternates side to side as the later type you are describing. I have worked these, and have made a number of reconstructions based on the evidence available (quite limited mind you!) The rough size of each chamber is 60 cm long x 30 cm at the widest. Normal loft height is about 30 - 35 cm.
The maximum volume there is roughly 120 LpM. ( If you run a search on 'blacksmith bellows' here you will find a number of earlier postings dealing with these. )
This bellows system will effectively create a 'ball of heat' in hardwood charcoal roughly 4 - 5 inches in diameter. Welding heats certainly possible. (The bigger problem is how fast the fuel is consumed, dropping unlit 'cold' charcoal into the heat zone.) Remember that Saxon and Viking Age pattern welded swords were all made with some variation on this basic equipment!

This all suggests to me that the needed volume of the later 'twin with bar' bellows may more be linked to fuel type and the required heat zone (as determined by work type undertaken). If you are expecting to forge weld large axes, you certainly need a larger heat zone available than if you are making simple hooks.
On size, there seems to be a lot of variation on both illustrations and working replicas of early bellows types I have seen.
Roughly, you see a length to width ratio on the individual plates of 2:1 or 3:1 as pretty common. There is also an ideal ratio of inlet to outlet diameters, 4:1 appearing to be an ideal. I expect this may be where the real tinkering may lie in an effective design.

My rough guess is that the later period 'great bellows', with two interlocked chambers stacked on each other, was introduced with the switch to rock coal in blacksmithing around 1300 +. This just an estimation, you would have to do further research on that. The advantage of a great bellows is that there is a larger reservoir of air to produce a longer, constant blast. At the same time, a fast snap of the wrist can force a sharp blast of air if desired. You would end up lifting less counterweight on each arm stroke than with the 'twin with bar'. 

If any readers have actually built and operated the 'twin with bar' system, I'm certain we all would like to hear of their experiences!

Friday, March 20, 2015

Antique objects / Bloom iron ?

On 19/03/15 12:54 AM, Jeff  wrote:

I see that barrel hoops are fairly flexible, but the iron from the bloom that *I* have ... seems to be fairly rigid even in the very thin bits. Is this a steel-vs-bloom-vs-cast-iron thing, or is there a trick to making bloomery iron flex?
Remember that you may certainly be looking at objects made of Bessemer mild steel (possible for anything after 1855) in those 'antique' barrel hoops. Most likely you would be seeing something pretty much like (or actually) a modern mild steel.

Individual iron blooms can vary considerably in actual carbon content, thus potential hardness / rigidity.
Ore type and particle size, layout of the furnace, operating temperature, size of charges - all can effect the potential results.
If we worked with that granular hematite for your smelting course, that stuff tends to the mid carbon ranges for example.
Even a single bloom usually varies across its diameter, typically the top surface having a higher carbon than the base. This difference will often get 'folded in' as the consolidation welding series is undertaken. (And the welding process itself can change the available carbon content.)

Proportion of other trace elements in the ore can also effect the effective hardness / rigidity. Phosphorus for example can certainly make the metal more brittle. This more a problem with natural bog iron ores, some of the rock based types. (One of the advantages of the analog we use here is that we have better control of the elemental content.)

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

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