Sunday, April 26, 2015

Ancient Metals = Ancient Fluxes ?

On 25/04/15 4:02 PM, Joel wrote:
   ...  Since in our modern world, we use mild steel to mimic wrought iron, there is a need for a wire brush.  What can be used instead as a Viking Age tool?  I've tried sand with limited success.  

What you are appearing to refer too is the forge welding process.
It is quite true that iron oxide scale itself will not fuse. The metal surfaces need to be made, then remain, as clean as possible.
What the addition of a flux does is two things:
1) Coats the surface of the iron to prevent contact with oxygen. No oxygen = no scale formation
2) Under the pressure of the hammer stroke, the (then) liquid flux squirts out - washing with it any dirt or scale that might have gotten between the surfaces to be welded.
Careful control of the fire oxidation / reduction atmosphere also obviously important to reduce potential scale formation.

Recent (say post 1855) practice with our modern steel alloys is to add a flux to assist with both functions above. (The best way to ensure the success of a forge weld is to start with clean bare metal surfaces!)
Here in North America, which has natural supplies of borax, it is borax that is the usual flux applied. This can either be chemically purified (water removed) borax, which requires only small amounts, but also is quite expensive. A lot of smiths (including myself) just use much cheaper 'washing soda' borax from the grocery store (like '20 Mule Team' brand). This is certainly messier - but only a tenth the cost.
The 'traditional' practice from England / Europe is to use a fine white silica sand as the flux. I fully admit that I personally have not tried this. You certainly would need much higher temperatures to get this material to stick, much less melt on to, the metal surface. Problem there is that oxide scale is starting to form * before * a modern steel has gotten hot enough to allow that same sand to fuse to, thus protect, the metal surface.  (One warning bell here - this practice likely pre-dates the introduction of our modern steels.)

Forge welding a piece of bloomery iron. (Image by Neil Peterson ?)
Ancient type bloomery iron especially, but also 'antique' (pre 1855) wrought iron have a quite different physical structure than modern steels. Both these materials always contain small amounts of glassy slag remaining from their initial smelting process. So in effect, both these materials are * self fluxing *, in so much as the glass contained tends to 'float' to the metal surface at forging temperatures. How much so would certainly depend on the initial purity (read quality) of the starting bar. A lower quality bar would contain more slag, which also makes it de-laminate more easily (but in combination should be easier to weld back together). This 'weld while forging' process is often over exaggerated by those less experienced with historic type materials. (You do * not * have to start * every * forging step at welding heat!)

We of course can never know exactly just how individual blacksmiths from ancient times might have undertaken specific forging steps. The pronounced grain in corroded bloomery iron objects can inform us about how the metal might have been folded and welded. On a microscopic level, remaining inclusions of certain slag compositions might suggest addition, and composition of a fluxing agent. It may prove possible to make some guesses based on close examination of 'hearth bottom' slags. Even collection and examination of tiny pieces of slag spattered out from the welding hammering itself.


On your observation on use of modern steel wire brushes to clean metal surfaces. Obviously there is no duplicate of this type of tool in the Viking Age tool box. I would suggest that the possible method would be to use a large 'whetstone', over the surface to be cleaned / welded, likely like modern practice of brushing, when the metal is hot. Remember that many of these whetstones are huge to modern eyes - imagine a block the size of a two by four as long as your arm! If made of a rougher sandstone, such a block would certainly allow for very swift cleaning of scale off a hot metal surface.

Viking Age whetstones - Ribe Museum - Ribe, Denmark.
It is important to remember always that our modern steels do * not * replicate the handling properties of historic metals. What may be easily accomplished with modern alloys and also modern coal / gas forges (and big anvils!) might be quite different than the working processes used with ancient metals and tool sets.

Thursday, April 23, 2015

Pre-Roman Iron Age in North Europe?

Scott wrote on the Bladesmith's Forum:

I have a hard time piecing together the history of Europe in the early Iron Age... Pre-Roman.   I get that east and north were generally Germanic and to the west was mostly Celtic.   I see plenty of examples of Celtic swords and I see the single edge Germanic swords and war knives.. and I know that the Germanic tribes adopted Roman swords at some point.. but what double edge swords were of pure Germanic origin .. if any?

Another thing I'm curious about but see very little in the literature is the nature of interaction between the Celts and Germans.  Obviously it was either trade or war ... but what details and evidence?  Obviously there would have been no written account until the Romans became involved.  But what does archaeology tell us?

If you define 'Iron Age' as 'marking the use of iron as material' - then the true Iron Age runs from at least about 1000 BC in Northern Europe.

One of the other definition problems is that mainland Europeans / British / Scandinavians all see the frame work of their own past marked by different events. So much of what us English speakers have access to is from Britain. The line between 'before the Celts' and after this invasion is fuzzy at best, and does appear to also mark the transition from a primary Bronze Age into the early Iron Age. The Roman period has sharp lines for initial start and theoretical end.  Then there is another fuzzy period around the 'Saxon Shores', when the 'Germanic' Angles and Saxons are invading and colonizing.
Complicating this is the whole very modern concept of national boarders. I mean, does a person living in North west France about 200 AD part of 'French' or 'Celtic' or 'Gallish'  culture? (Or maybe even some weird mix of Roman plus all of the above?)

Part of a big problem for me is the whole concept of the 'Viking Age', which is defined by two British only events : Lindesfarne in 783 and (usually) the Norman invasion of 1066. Some argument at least can be made for an end to the true Viking Age some place about 1000 - 1100, with the growth of centralized kingdoms and gradual adoption of a more feudal structure. The notion that the Scandinavian culture sprung to life fully formed overnight is obviously unrealistic!

I was a bit surprised when I managed my one trip to Denmark that there they break the lines at 'Iron Age' to 1000 AD and then 'Medieval', running afterword. (I guess I should not have been!). North Germany and Denmark into Scandinavia was relatively untouched by Roman culture (quite unlike the rest of Europe).

Some histories out of mainland Europe will mark 'Migration Period', which usually is some (again fuzzy) time 'post Roman - pre Medieval'.  This is at least a bit better than the older seen line of 'Roman to Medieval', given as the 'Dark Ages'. (Honesly, I'm never quite sure just when that is supposed to cover - at least in terms of end dates.)

'Migration Era' grave goods set - fighting knife and small tool knife


(left) 'Celtic Iron Age' - c 100 BC
Iron sword locked into decorated bronze scabbard with cast bronze fittings.

If your interest is clearly on * object *, your best bet might be just digging into the archaeological record. Not a simple task, as you are unlikely to find a single point reference that is going to help you. Its going to be a tedious task of checking dates and find locations.
One of the huge problem is one of simple survival of iron objects. The Celts of La Tene are a primary * Iron Age * culture. But what do we find? Bronze objects! Iron swords corroded and locked into decorative bronze scabbards, with only rare x-rays giving any clue at all about physical structure of the blades.

Complicating this is the whole modern tendency to apply our current 'best technical practice' backwards. 'Steel' means something quite different when applied as a descriptor by an archaeologist to an Iron Age blade - than it means to a modern bladesmith.  Original bloomery iron materials most often had little or no carbon - and also have a quite different physical structure from our modern alloys. It is clear when you look at primary archaeological reports that our current practices of heat treating were only being developed and more randomly applied through the 'Late Iron Age'.

See also some earlier posts:
'Iron from Celtic to Early Medieval'
'Iron Age vs Viking Age'

Exploring the Viking Age in Denmark

Wednesday, April 15, 2015

Icelandic Grass Sod Furnace - April 25

From Fall 2007 through Fall 2008, plus one in Spring 2012, DARC mounted a series of five iron smelts specifically aimed at re-creating Viking Age furnaces from Iceland. The archaeology was based on excavations by long time friend (and unofficial adviser) Kevin Smith at the Hals site. This was a long term, 'industrial' scale iron production operation, with the remains of a number of bloomery iron furnaces uncovered.

As a refresher, the Icelandic system is basically a cone made of piled up grass sod, with a cylindrical hole in the centre (the furnace). At Hals, these were constructed entirely above ground level. The cone was then boxed with timbers. The space between the timber and cone was then filled with earth to create a working surface at the top level of the cone / furnace mouth.
The full discussion of the Hals evidence and how it is being interpreted can be found on the main Wareham Forge web site : 'Working towards an Icelandic Viking Age Smelt'
The descriptions of the previous five experiments in this series can be found on the main Wareham Forge Iron Smelting documentation

The original plan for 2014 was to return to the Hals / Icelandic project.
The furnace construction was started, but with one thing following another (for me personally), the build was never completed, and no actual iron smelts were undertaken.

For a discussion of the current build see : Return to Hals / Oct 10, 2014
This year, I fully intend to return to the Hals / Icelandic experimental series. The cancellation of Early Iron 4, originally scheduled for the weekend of April 25, puts an available hole in my schedule. Now that the snow has (finally) cleared off the smelting area at Wareham, I have been able to assess the condition of the work from last fall.

Build in October 2014
With the help of Neil Peterson, last fall the construction was started on a full sized build of the Icelandic pattern furnace.
- To conserve materials, the area where the previous smelts in this series had been built was fully cleared out. This gives a hole into a roughly two foot high earth bank, reducing the amount of timber framing required for the full above ground construction.
- By a nice coincidence, clearing ground for a planned garden means pulling off more than enough grass sod to allow a full 60 - 70 cm height.
- The central shaft is being created by using a metal form - in this case a roughly 35 cm diameter section of metal air ducting pipe.
- At the front is a stone (and brick) support to allow for a taping arch. The interior gap will be filled with more grass sods. The flat stone seen should support sods making the front upper wall, if the lower taping arch needs to be opened.
- The general plan is to set a ceramic tuyere near the top of the stone work - but inside the interior space. Some refining of the size of this stonework still needs to be made to ensure the normal 23 degrees down angle can be used.
- This is intended to be a top extraction, with the space between the conical sod walls and the space at ground level filled with earth removed when clearing the needed space into the bank.
- The ore for this smelt is likely to be the bog iron ore analog (from iron oxide powder).

Note to Readers:
The smelt itself is set for SATURDAY APRIL 25.
This will be the usual 'semi-open' event here at Wareham.
Individuals interested in attending are welcome - but should contact me via e-mail to let me know how many people to expect.  Like usual, there are plenty of 'dirty jobs' to be undertaken.
Pre-heat starts for about 9 - 9:30 AM
Main sequence start for about 11 AM
Extraction expected about 4 - 5 PM

Thursday, April 09, 2015

Early Iron 4 - CANCELLED


There has not been the support of this event that we had hoped.

The deadline to make a required $1000 deposit to the Ashokan Center was April 10.
There are simply not enough reservations in hand to cover even this amount.

After some discussion between the event organizers and the intended feature demonstrators, we have decided just to cancel Early Iron 4 at this point in the calendar.

There is some hope that the event might be re-scheduled for a point later in 2015, or perhaps 2016...


 

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

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