Sunday, December 21, 2008

Blade Construction in the Viking Age - PROBLEMS

A question from NORSEFOLK

I'm planning on doing a reproduction of a historic piece from
Canterbury, Kent, England. It's a folding knife with a carved bone
handle (pictured here:
... As construction goes, I'm primarily concerned with the nature of the
blade steel (Was it a composite blade with a hard steel edge welded
onto a softer iron back, a single piece of steel, pattern welded, or
some combination of methods, etc.).

A couple of things:

All that is listed in Viking Artifacts by Graham-Campbell (the source of the quoted image) is 'iron blade'
Not overly surprising, as he is an art critic, and is often very short on technical details. (The description runs four paragraphs - two of which are about the carving style on the handle!)

(You might also want to take a look at something I'm working up on VA knives at : )

From a general understanding of Norse knives (and tools in general) a couple of things you need to consider:

Most of the metals used in VA cutting tools are significantly softer metals than a modern maker would consider using! The largest percentage are forged from plain bloomery iron. This material can vary in carbon content, but generally will have very little to virtually no carbon content at all.
For that reason, the 'most accurate' raw material for a high end reconstruction would be antique wrought iron. (And no - you can not harden that stuff through heat treating.)
For general purposes, if you used a modern mild steel, then water harden it (no temper) and you would be creating a blade 'as good as the average' for the VA. (As a skilled smith, you realize that the texture is bit different, but in this item that is not likely significant.)

I mention this, primarily as many focus on the more unusual blade material techniques also used by the Norse. If you took a look at 100 knives, almost all of them would be plain, unaltered 'mono block' blades. There would be some attempt to pick slightly higher carbon portions of a source bloom / currency bar if that was possible.
Against this, there are *some* artifact blades that show a number of other billet creation methods (thats manipulating the starting block of metal, before you forge to the blade itself):
- Case hardening
- Lap welding (next most common to mono block)
- Block forming
- Carbon core
- Piled strips
- Full Pattern welding.
Pattern welding (layered rods, twisted, welded into billet for core of blade) is almost without exception used for extremely high status objects. On sword sized blades, it has a function - that of allowing the blade to flex out of true on impact and then spring back to straight without damage. On knife sized blades, pattern welding is for decoration effect only - and is more likely to *lower* the edge holding ability (compared to a plain high carbon mono-block edge).
(Image - detail of Pattern Welded sword from Denmark)
Bear in mind, for that same theoretical 100 blade sample, it would be surprising to find more than one or two that had been physically tested for specific carbon content. At least in the past, those tests are destructive ones, requiring sectioning the blades (cutting them appart!). Some construction methods, where differing carbon layers are combined, may show as visible changes in corrosion rates. This is especially true of pattern welded blades, where the twisted layers of the core will be quite obvious. (But believe me, determining the exact number of layers uses is often guess work!)

To make matters worse, the language used by archaeologists is not as precise as the skilled bladesmith would like! To the smith, 'iron' is a very specific metal material, as is 'steel'. Most certainly, when an archaeologist says 'steel', what they really mean is 'bloomery iron with some carbon included'. This historical material is just as different from modern alloy steels - as antique wrought iron is from industrial mild steel bars. So you have to take those material descriptions with a grain of salt. (And a pretty large one! Remember how archaeologists rarely use the term 'bronze' any more, but instead you see 'copper alloy'. The differences between VA bloomery iron and even late medieval iron is at least as significant.)

This does not directly answer the question of 'what is that folding knife made out of'. It does suggest that as a modern bladesmith, you will have to make some determination on how your available materials must be chosen against your intent for the finished reconstruction.

There is a reason why a small sharpening stone is such a basic personal item in the Viking Age. With blade metals generally quite soft - you would be sharpening knives almost every time you used them. This is born out by the extremely worn condition of so many of the artifact knives that have found.


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

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