Saturday, February 21, 2015

Bladesmithing Interview - Part 2

3.Have you used smelted bog iron to make knives or swords? How do they perform?

I have made a number of small knives as replicas of known Viking Age types, plus some modern designed knives utilizing bloom iron as one component (Hector's Bane the best example there).
For my own work, I am concentrating on re-discovering lost historic smelting methods, which is certainly different than using the processes to produce the best possible blade making materials. This is an important distinction.

Historically, the aim of the smelt master was not to produce blade materials, but instead to get the largest bloom of iron that could be easily forged for general purpose work. Our modern understanding of how carbon (or other elements) can modify the base iron for ideal cutting edges just did not exist. Even in the Japanese tradition, there was no clear knowledge of how modifying a furnace or changing aspects of the firing might produce a specific result. Instead, the blade maker would use experience to selectively pick pieces with hoped for characteristics out of a larger pile of random quality bloom fragments (based on colour, crystal structure, fracture lines). Here I am talking about Northern European, Early Medieval, methods, also with the initial reduction of ore to bloom (not secondary modifications like 'hearth steel' or wootz).
So the most common base material past on from the smelt master into the hands of the Viking Age blacksmith was simple bloomery iron, compressed to working bars. This material would have next to no carbon content, and would contain varying amounts of slag tendrils (even inside the same source bar). As each bloom itself varies in its carbon from top to bottom, most certainly accumulated experience would teach some parts / methods of working resulted in blades with slightly better edge holding than others. There would certainly be no kind of predictabililty of results as is enjoyed by modern bladesmiths, working with our standardized industrial metal stocks.
'Bloom Seax' - Simple Norse era natural branch handle

What this means is that historic blades of bloom iron (or accurately created replicas) are simply not hard - and they just do not hold an edge. So much so that one of the most common personal objects for a Norse or Saxon male was a small sharpening stone, worn attached to the belt. Straight bloomery iron blades require almost constant sharpening! You also see this in the artifact knives, with most blades well worn down from all the sharpening during their use life.

For the modern designs, I use the bloom iron specifically to highlight its unique texture. Blades like Hector's Bane have bloom iron exterior slabs forge welded to a carbon steel core. As with other inset cutting edge styled blades, it is this modern alloy core that is forming the actual cutting edge. So the bloom iron is not really a functional component, but a decorative one.

'Hector's Bane'

Honestly, given the high skill and massive labour needed to create bloomery iron in the first place, this material is just to valuable in my eyes to waste. So I have never undertaken a series of destructive tests to firmly determine the absolute compairison properties of bloomery iron. Given the wide variation between individual blooms, I'm not even sure how useful any comparision to modern alloy steels would even be.

No comments:


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

COPYRIGHT NOTICE - All posted text and images @ Darrell Markewitz.
No duplication, in whole or in part, is permitted without the author's expressed written permission.
For a detailed copyright statement : go HERE