Monday, December 22, 2008

Pattern Welding on VA Swords

ABSTRACT * - A discussion on pattern welding as used on Viking Age sword blades, considering why the elaborate technique may have been used, and how such objects may have been finished...

Adapted from a posting to NORSEFOLK

To quote : 'Charles from Oz'

>> Some of the examples of pattern welded blades may not have been designed
to be decorative, but pattern welding was a process that was simply used in their construction.

>> The assumption that all pattern welded blades were pretty is
conjectural, in that the pattern only shows after the blade has corroded. This is what exposing the pattern in a pattern welded blade is... controlled corrosion.

>> This process, of pattern welding, has been used by smiths for a very
long time, and as we know it's mainly for economic reasons. If pattern welding were simply for decoration, then there would be a "lot" of pretty Roman spathas out there ;-)

This brings up several points, which Charles obviously must be aware of, but did not detail in his original posting. For those who know about this topic already, sorry if some basic information is repeated. This * is * a rather arcane area of the 'art and mystery of the blacksmith'.

Just as some (deep) background, I have touched on the topic of Pattern Welding, and how it relates to the Viking Age, many times on my blog Hammered Out Bits. A lot of these short pieces have been worked over versions of answers to questions posed here on NORSEFOLK:

The earliest pattern welded swords that I have stumbled across are 'Late Roman' - from about 100 -200 AD or so. Sorry, I have not studied this time period in detail. I had forged a Gladius pattern as a simple pattern weld (two layered and twisted cores with spring steel edges) as an exercise in 'creative history'. I was surprised when a customer who is involved in Roman re-enacting was keen to purchase the sword. She said it was identical to some artifact samples from that period. Which at the time lead me to take at least a fast look over those artifacts.
(details on the blade 'Sword of Heroes' at )

One long standing "theory" behind the purpose of the North European pattern welded blade is this:
The centre core of the blade is made of two or more long rods, each themselves made from a stack of metal plates. These starting stacks alternate between a soft, flexible iron (no carbon) and a harder, more rigid 'iron with carbon' alloy. Both of these metals would be of course bloomery iron, so would also have a fibrous texture with slag inclusions. The intent of the layers is that the soft iron tends to bend to absorb shock, while the hard 'steel' tends to resist any deforming. When you take these layered bars and twist one clockwise and one counter clockwise and then fuse them together by forge welding, you in effect create a pair of 'coil springs' running down the centre of the sword. This allows the blade to absorb a certain amount of impact shock, yet making it snap back to straight again after. Now the smith can attach (again by forge welding) two medium hard 'steel' cutting edges, metal that normally might shatter under the stress of combat. The end result is a sword that is both more durable, but at the same time stays sharper, than a plain single bar of metal could be.
I deliberately say "theory" here. That is because as far as I know, no one has ever actually ** tested ** this in practical terms. The only way to prove the difference between pattern welded versus mono block blades would be to make up a number, then test them to destruction. A real hand forged pattern welded sword is an object that takes weeks for a highly skilled and specialized artisan to make. The cost reflects this, at several thousand dollars per sword blade. (Hey - if some Museum wants to fund this as a research project, I'd sure love to make the swords. I normally * start * prices at $200 per linear inch for swords!)

Some modern researchers have suggested that the reason for the pattern welding technique is in fact a bit different. Instead of a method to utilize high quality metal to make exceptional quality blades, it was intended as a means to take average quality metals to produce 'good' quality blades. Again, this might be possible to qualify through a series of destructive tests. Personally, I find this logic chain unlikely. The skills required to create a pattern welded blade using the available Viking Age tools are extreme at the least. The repeated forge welds in small charcoal fires, the small size of anvils available, the massive amount of time required for smoothing and polishing - all massively increase the 'labour cost' of such weapons. Always, the highest skilled smiths commanded (and demanded) the use of the best available materials. So as a working smith with experience with VA tools and techniques "I'm just not buying it". This viewpoint of 'poor materials through elaborate technique to average results' can be found in the literature, however.

Now Charles points out a rather important qualification. I do have to disagree a bit on the detail, but hold with the spirit:
" ...the pattern only shows after the blade has corroded. "

I think what he is referring to is that modern bladesmiths (myself included, see ) will use equally 'modern' acid solutions of various types and combinations to etch the finished smooth surfaces of a pattern welded blade to highlight the layers. What happens is that the various individual layers, composed of differing carbon contents and / or alloys, react differently to the chemicals. A plain high carbon steel for example, goes a dark black colour, while antique wrought iron takes a 'braided rope' like surface texture. He is absolutely correct that in essence this is nothing more that controlled corrosion. It is most important to remember that these acid solutions ** did not exist in the Viking Age **. So the changes in relief and colour so desired by modern artisans would just not be possible to ancient swordsmiths. (A side issue here is that those deep colour changes, typically produced by etching with ferric chloride, are only * surface * effects - they will quickly wear off under normal use of the blade as a working tool.) Modern smiths also highlight the layered effects by including nickel based alloys that (essentially) did not exist before the Modern Age.

In the Viking Age, controlled corrosion could be undertaken using natural based chemicals. The primary ones available would be vinegar (an acid), urine (a caustic base) or salt water (accelerates oxidation). I have done some simple tests with all three, and have found that the vinegars give the best effect, a subtle darkening of the component layers at differing rates. So right off the start, it was possible for VA smiths to increase the contrast between layers and so make visible the distinctive patterns on pattern welded blades.
Now there is another possibility. The differing carbon contents of these starting layers changes the relative hardness of the layers. So when you polish a layered object, the polishing material (be it stone or modern sand paper) cuts slightly faster and deeper into the softer metal layers. The end result is extremely subtle - you have to catch the light on the finished blade just right to see it. At just the correct angle, the pattern suddenly shimmers down the length of the blade. I mention this, as I have read (other commentators, not my own primary source research!) that some of the Sagas refer to things like 'a serpent was seen shimmering down the length of the sword'. Such a statement would not be fanciful - its pretty much an exact description of what is visible.

Truth is - we will never know.

No artifact blade remains in good enough shape to determine what degree of surface finish was used in the Viking Age. This refers just to amount of surface polish (which my own opinion is far less than what is normal to modern blade makers). As to some type of controlled corrosion effect applied to pattern welded artifacts, this also is unknowable. The only suggestion is an unprovable 'cultural' one. Creating a functional pattern welded sword in the Viking Age was the work of only the most skillful of master swordsmiths (sword makers themselves set above typical blacksmiths in skill level). These were 'royal status' objects, hugely expensive and unusual to rare, even in the eras of their greatest production. The blades are commonly set with elaborate guards and pommels, further enhancing their secondary (?) role as status objects. (The sword from Sutton Hoo is not only the most complex pattern welded object known from the period, it is also by far the most elaborately decorated, with gold and inset garnet work - as the classic example.)

(this has gotten long enough - I have something to say about pattern welding on knives, but will leave that for another posting)

* - Since I now am cross posting from here on to FACEBOOK, that system uses the first lines as its summary for describing postings.

1 comment:

STAG said...

I must admit to subscribing to the "one smith with a variety of different quality materials and have to make the best of it" theory myself. For every sword good enough for a king, there would be thousands made from salvaged nails and broken plowshare points that the lesser nobility would be able to afford. Of course, I have no evidence to support such a statement, it just seems logical.

I would not disagree with the premise that the vast majority of tricky products (like swords) would have been made by the millenium equivalent of General Motors rather than the "under the spreading chestnut tree" style of smithy. Not every automaker can stay in business making Lambourgini's, some have to roll out Volkswagons and K-cars. But (if I may push the analogy further) it doesn't take a huge factory to do a little mechanical work in your back yard. The poet doesn't seem to be suggesting more than that.

The idea of currency bars is kind of interesting, after all ingots of metal from lead to tin to silver are pretty commonly found in panic burial hoards, and in the holds of sunken ships. I don't seem to find the term "currency bar" this very logical phraseology yours or is it a term which is in general use?

On a sort of related note, Gabrielle on the "Lost Fort" has posted some pics of recently uncovered late Roman stuff in Northern Germany. There is an oxen shoe pictured, among some weapons. Very cool, you should check it out.


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