Sometimes I just can't stand it!
The piece before is copied directly from a post I wrote this morning for the Norsefolk discussion group. I suppose it comes off a bit high handed.
Several loud voices had been droning on about Viking Age armour types. Which morphed into grand statements about VA blacksmithing skills. And then the comparisons between Japanese (late Medieval and later) sword making techniques...
I can see by a shift to a textile related subject that many are fatigued by the recent thread on metals, armour, weapons and blacksmithing methods. I also have kept out of this, until I just could not stand it anymore.
I have seen an awful lot of theory (read WAG) and little based on *applicable* direct knowledge / experience.
Techniques based on 20th century (post 1855 Bessemer steels and propane gas forges)
experience is of limited value to clear understanding.
|Working a VA 'sand table' forge|
Modern metals just do not behave like historic ones. Antique wrought iron is a distinctively different material than ancient bloomery iron. Propane heat has its own characteristics, as does rock coal, as does the only fuel utilized in the VA, which is charcoal. The equipment set up of the forges for each is completely different. The welding processes used at the forge retain the same base mechanism, but the actual processes used in detail are different with different iron metals and also with different fuel/forge set ups.
Popular culture ideas of how forge welding *actually* works are simply quite wrong.
Both wrought iron and bloomery iron have a distinctive chemistry and a distinctive physical structure. You make some shapes using quite different methods than when working with modern materials. Core to this difference is the existence of microscopic layers of glassy slag within the body of the metal. Any given piece of material will vary not only between pieces, but even as different spots within the same block.
This is also completely the case with the amount of carbon present within an individual iron bloom, which most definitely are not uniform in alloy content (as our modern metals are).
This difference in structure due to slag content is critical to any possible understanding of the relatively difficulty of creating shapes using VA type iron metals.
|VA iron plate cook pot|
Simply put, the slag inclusions will cause the metal body to crack and shear, especially when subjected to strain, especially as the piece of metal gets thinner. These are almost always *diagonal* lines - virtually impossible to forge weld tight again when creating thin pieces.
That is why 'currency bars' from the VA most commonly have one end flattened out to a paddle shape. This was a clear indication of the relative quality of an individual bar. Metal with larger amounts of slag still remaining would shear as it was flattened.
*This* is why large thin plates are not seen in Viking Age artifacts. Almost without exception, iron plates are never any wider that 20 cm. Those plates that do exist are quite thick, with thickness in the range of 4 - 6 mm (that's 1/8 to plus 1/4 inch for the Americans). Even the thinnest is two to four times as thick (and heavy) as modern steel sheet used for almost all contemporary armour making. (Check the actual thickness of the metal in an artifact cooking pot.)
People hold up Japanese forge working (especially bladesmithing) techniques without understanding exactly what the purpose of those elaborate folding and welding techniques *is*. The core purpose of the Japanese method is to produce a highly refined block of metal, eliminating as much of the slag content as possible. A secondary purpose is to control the carbon content of the iron alloy, more importantly to 'average' out the available carbon within the block. The theoretical existence of many thin layers is totally incorrect. (Due to carbon migration at welding temperatures, much over '1000 layers' those individual layers totally blend to a consistent mass and effectively disappear.)
Those who talk about the difficulty of welding twisted cores for VA pattern welded blades either have never actually undertaken this process themselves, or more likely are referring to early *failed* attempts to duplicate this process. These experiments in the 1960's have been widely duplicated in popular illustrations. (The most obvious culprit is the 'wrinkly people book' - The Vikings, published in the early 1970's)
|My own 'Sword of Heroes' - 2 cores, each 9 layers|
No, gentle readers, the *correct* way to forge weld up a pattern welded blade is to start with a set of flat plates (typically 3 - 4 cm wide, 3 - 4 cm tall and 10 - 15 cm long) and forge weld that flat stack into a block. Then the block is drawn out to a long octagon. Then that is what is twisted. It is then (typically) hammered back into a square cross section. Only then are the individual core rods welded back into a long rectangular shape to create the starting material for the eventual blade. (And yes, this is exactly how *I* do this.)
The exceptional sword found at Sutton Hoo is consisted of a total of eight central core rods, each rod forged from a welded block made up of 7 to 9 layers (x-rays not entirely clear), with an edge layers applied in addition. The total number of welds required far exceeds those needed to create a Japanese technique blade.
Difficulty is based on the number of welds required - not simple layer counts (which is a *geometric* progression after all.)