Thoughts on the Origins of Pattern Welding

(originally a post to ARCHMETALS)
> Date: Sun, 22 Jan 2006 15:09:50 +0000
> From: Edgar
> Subject: Did ancient iron improve by reworking?
> Regarding iron produced in Britain from the beginning upto the late Saxon period.
>... I had wondered if the knowledge of improving a piece like a sword by hammering and >bending and reheating, was gained almost accidentally this way.

An unresearched observation:

I had always been puzzled by just how the whole idea of pattern welding could have developed in the first place. (as in the N. Europe type of layered steel for weapons - low layer counts with multiple twisted rods.) This may seem a bit long winded - but there is a point...

My group here has been trying to work backwards from proven small smelter methods towards ever greater use of Viking Age replica tools and smelter layouts as suggested by archaeology. Its a big task, compounded by the fact we have no easy access to institutional libraries and are funding the whole thing out of our own pockets on weekends away from our normal jobs. (www.darkcompany.ca/iron)

At this point I've done over a dozen smelts - and have collected a pile of blooms that I have made. (Its a well known truth that everyone seems to keep EVERYTHING up to about the 10th smelt, then you start to wonder what to do with all that stuff.) I just started earlier this month starting to cut up some of the blooms and consolidate them into actual bars. A couple of things I've noticed:

- We have found it easier to make a 7 - 10 kg bloom than a 3 - 5 kg one. This may have a relation to smelter size, we are working with the 25 - 30 cm dia and roughly 60 cm height suggested by the archaeology. It seems that you need a certain amount of ore and smelting time to get a 'seed bloom' started. Piling more ore in after that just appears to enlarge and condense the mass. There is certainly an economy of effort and raw materials in producing a larger bloom.

- This is balanced with a physical problem on the OTHER end of the smelt. If you have a 10 kg plus bloom, how do you manage to work it? A metal mass that size takes a lot of effort to cut for example.

- This is compounded by a second related problem - How do you heat up that large a chunk of metal? When first extracted from the smelter, the bloom is white hot. Great! Its the SECOND and subsequent heats that are extremely difficult to maintain. A smelter makes a very awkward forge. You need a huge pit forge if you attempt to use that method. (There should be clear evidence of this.) There is also a check back related to our evidence of tools, VA hammers for example are 'small' related to modern forging tools (large VA hammers are more to the 1.5 kg range)

- As I have started cutting and consolidating some of the smaller blooms. I have certainly found at least * our * blooms can vary considerably from one side to the other. (Yes, I hear the warnings about how these modern blooms may not compare to historic ones!).

This is the meat here.

In the process of compacting, folding and welding a bloom fragment to a bar it becomes obvious (to this experienced smith) that you are dealing with metal of differing quality. Workability and effective welding temperature ranges noticeably. One of the fragments I worked a couple of weeks back ranged from a soft iron to virtual cast iron carbon content, all across a fragment at about 1 kg. This fragment has been consolidated, flattened, folded in half and re-welded. At this point I'm sure that the bar is consistent enough to take to the forge and create some object. Obviously this bar would range in carbon content within itself. * If * the translation from high carbon to low was even in the starting fragment, I'd end up with something like this:

LLLLLMM
LLLLLMM
HHHHHMM
HHHHHMM

You can see that if I took that same bar and forged it into a cutting tool at this point I'd end up with something with a hard cutting edge and soft back (with a good strong medium carbon tang).

If this same bar requires a second draw and fold , I'd get this:

mmmmmmh
llllmmh
llllmmh
hhhhhhh

The layers are thinner now - but you can see that if I took this bar and forged a knife, I'd end up with a hard lower edge, hard point, with a medium back and a center running from hard through to soft.

Creating a 'block formed' layered edge would result just from the smith paying attention to the 'hammer feel' of the bloom as it was compressed to a bar.

We also have clearly noticed that a quenched bloom can show surface colours that indicate the relative carbon content as well. We certainly have selectively cut and sorted bloom fragments this way. Individual fragments consolidated then yield an assortment of carbon content quality bars. In the forge these can be selected for suitability of purpose or combined for effect.

Darrell