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James Simonds

early medieval steel. to bloom or not to bloom?

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Hello

I am a new amateur bladesmith and also writing a historical fiction book about the late viking age. The story centers on a smith from lower saxony taught in the western swordsmithing ways who ends up in Uppsala in the Norse kingdom of sweden learning about Norse swordsmithing and then creating a fusion between the two styles which i find very interesting. (thats not the main part of the story, its a side note but i want it to be beleivable).

I am trying to make my book relatively historically accurate, or as i said, believable. This is not a scholarly work and i am not splitting hairs over the minor differences between hammer shapes or whatever, i am looking at the big picture. correct period and location sword/axe/spear/seax design and use etc. I have been researching this all very thoroughly, going as far as to forge my own seax with Owen Bush (there is a post somewhere about that). i am very comfortable about the differences in Norse and Western european weapon design etc. and the forging process.

What i am utterly struggling with, and i am clearly not alone, is how the two different areas made and used their steel. I assumed it was pretty much known how medieval weapons were made in terms of metallurgy and process. i knew vaguely about bloomery steel, de-carburising and fining in general. but my recent research has turned up so much conflicting information about steel production and use that i feel like i have lost track of what is right. so, with that context, i am hoping you fine folk can help me out. and yes, i have read some other threads on this forum already but again, the often confused me more than helped in this particular case! this is because they mostly focus on what is possible, i want to know what was done at this specific moment and place in time.

 

Here is what i think is my understanding of it and my main gaps.

Norse 11th century swords were often pattern welded from a mixture of various grades of steels and irons. this was because the material was variable and mixing it in this way guaranteed a pretty good average effective material property and a blade without random weaknesses. also, it was developed into a visual art form. for things like axes, they often welded a steel edge onto an iron body. probably to reduce steel use.

Germanic/frank 11th century swords were not pattern welded. they 'may' have been single piece iron (lower quality ones) or forge welded bars with low carbon centres and high carbon edges/exterior. some may simply have been single peice mono medium or higher carbon steel (fancy ones).

 

I think all that is correct.

 

Here is the problem. how did they get that steel and was it a different process in each area or a mix? i have heard so many different theories and i cant get to the bottom of which is correct. please note i am NOT talking about imported crucible steel from asia, Ulberht swords etc. i am talking about indigenously smelted and forged blades.

 

1. Blister steel. wrought iron was heated with a carbon source and forged, repeatedly, until a decent outer layer was hardenable steel. OR allowed to crack and the layers of steel harvested for further processing or forge welding. i get the impression this might be later than 11th centruy. could a german smelter have been using this? doesnt seem to be evidence that Norse smiths were using this process.

2. crucible steel. some sources swear the Europeans were using this technique in the early middle ages. i am far from convinced. this seems dubious at best. either way, you dont pattern weld crucible steel surely?

3. Bloomery steel. I cannot get to the bottom (and this is why it is my main question) of whether you can reliably get sword making quality steel from the bloomer furnace or not. i have watched a dozen videos, talked to lots of people and read articles and websites. the bloomery iron process is clear but most sources say this method as done in the middle ages produces pretty much pure (low carbon) iron for making wrought iron, that is then later processed into steel. However, some also swear blind that they could make ready to use steel by this process (after all, the japanese method essentially yields bloomery steel but with very different raw materials). some also say that you often get steel on top of the bloom, iron in the middle and something near cast iron at the base so the Norse smiths would take these different materials and mix them, hence the pattern welding.

If they did use bloomery steel, how was the process different to getting bloomery wrought iron? different conditions? different types of fuel or furnace? different understandings? what is the truth here? its blowing my mind trying to get definitive evidence of this being used for steel production in the time and location i am interested in. It is clear that bloomery iron was made in both Norse and Germanic lands during this time, the question is, was bloomery steel in either?

4. Hearth forge. you take your wrought iron bloom and heat it with a lot of charcoal in the different furnace design with the shorter tower etc. and you increase the charcoal/iron ratio to create a carbon rich atmosphere. the result is a higher carbon bloom.

 

So, can anyone help we decide on this question before i commit e-pen to e-paper about the different smithys my protagonist works in? many thanks

 

 

Edited by James Simonds

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2 hours ago, James Simonds said:

 

Here is what i think is my understanding of it and my main gaps.

Norse 11th century swords were often pattern welded from a mixture of various grades of steels and irons. this was because the material was variable and mixing it in this way guaranteed a pretty good average effective material property and a blade without random weaknesses. also, it was developed into a visual art form. for things like axes, they often welded a steel edge onto an iron body. probably to reduce steel use.  Pretty much, as far as we can tell, although I have seen at least one axe that was forged from medium-carbon bloom.  We tested it.  That said, pattern-welding was dying out across all of Europe by the middle of the 10th century.  The standard rationale is "superior metallurgy replaced the need for pattern welding,"  but it could easily be something else, like the demand for more swords than pattern-welding could produce.  

Germanic/frank 11th century swords were not pattern welded. they 'may' have been single piece iron (lower quality ones) or forge welded bars with low carbon centres and high carbon edges/exterior. some may simply have been single peice mono medium or higher carbon steel (fancy ones).  Yes again, as far as we can tell.

 

I think all that is correct.

 

Here is the problem. how did they get that steel and was it a different process in each area or a mix? i have heard so many different theories and i cant get to the bottom of which is correct. please note i am NOT talking about imported crucible steel from asia, Ulberht swords etc. i am talking about indigenously smelted and forged blades.  Theories indeed!  They were making steel and iron everywhere using as many methods as there were ironmasters.  

 

1. Blister steel. wrought iron was heated with a carbon source and forged, repeatedly,   Not forged until a decent outer layer was hardenable steel, at which time it was stacked and welded to produce a reasonably homogeneous steel PROVIDED that the starting iron was highly refined and as slag-free as possible. OR allowed to crack and the layers of steel harvested for further processing or forge weldingNo. i get the impression this might be later than 11th centruy. could a german smelter have been using this? doesnt seem to be evidence that Norse smiths were using this process.  I have not seen much in the way of 11th century Norse smelting site reports.  Lots of (well, three or four) 8th and 9th century, a couple of 10th.  Lots of fired clay lying about, which could be the remains of case-hardening boxes.  Or just fired clay from making hearths.  No way to tell for sure, but no really big furnaces either, so the whole blister steel thing may be out for the Norse.  It was certainly in use elsewhere on the continent.

2. crucible steel. some sources swear the Europeans were using this technique in the early middle ages. i am far from convinced. this seems dubious at best. either way, you dont pattern weld crucible steel surely? Alan Williams is pretty persuasive, but yeah, there's no real proof.  Mark Greene of this forum proved he could use the Evenstad hearth-melt technique as described by an 18th century Norwegian to produce a slag-free high carbon steel.  And, there is a big difference beween the "crucible steel" Williams was thinking of (which would be medium-high carbon similar to Huntsman in the 1770s) and ultra-high-carbon Asian crucible steels like wootz.  And yes, you can pattern-weld with them, but why would you?

3. Bloomery steel. I cannot get to the bottom (and this is why it is my main question) of whether you can reliably get sword making quality steel from the bloomer furnace or not. i have watched a dozen videos, talked to lots of people and read articles and websites. the bloomery iron process is clear but most sources say this method as done in the middle ages produces pretty much pure (low carbon) iron for making wrought iron, that is then later processed into steel. However, some also swear blind that they could make ready to use steel by this process (after all, the japanese method essentially yields bloomery steel but with very different raw materials). some also say that you often get steel on top of the bloom, iron in the middle and something near cast iron at the base so the Norse smiths would take these different materials and mix them, hence the pattern welding.  Oh, yes indeed!  It is quite possible to make steel in a bloomery furnace.  Or even cast iron, but that was considered an accident.  If you read all the pinned threads in this section, and in the "pinned bloomers and buttons" forum further down the page, you will get all the theory and practice you need to know how to do either iron or steel in the same furnace.  Depending quite highly on your ore and your charge rates, as you'll see when you read about it.  Basically, though, it takes more charcoal burning faster to make less steel, less charcoal burning more slowly to make more iron.  That's why steel was always more expensive, even when labor counted as nothing.  Ore and charcoal are valuable.  

If they did use bloomery steel, how was the process different to getting bloomery wrought iron? different conditions? different types of fuel or furnace? different understandings? what is the truth here? its blowing my mind trying to get definitive evidence of this being used for steel production in the time and location i am interested in. It is clear that bloomery iron was made in both Norse and Germanic lands during this time, the question is, was bloomery steel in either? Yep.  The old Roman steelmaking center in Styria (south Austria, Roman Noricum) was renowned for the "natural steel" its shaft furnaces produced well into the middle ages.  This was due to both the ore (siderite, iron carbonate) and the skill of the furnacemasters.  The Norse were limited to bog ore, which is a little harder to make steel from directly.  This may lead to...

4. Hearth forge. you take your wrought iron bloom and heat it with a lot of charcoal in the different furnace design with the shorter tower etc. and you increase the charcoal/iron ratio to create a carbon rich atmosphere. the result is a higher carbon bloom.  You don't do it with a raw bloom, it needs to be somewhat consolidated first.  A big lump is slower to melt, and that is what the idea of these is.  The aforementioned Evenstad described the process as he had seen Norwegian farmers use in the mid-18th century.  Chances are it had been around a lot longer than that, especially given the relatively tiny hearths found on Viking-age smelting sites.  One large-ish short shaft furnace to make wrought bloom, two or three smaller bowl furnaces to either refine the bloom OR make hearth steel.  The end product is basically the same as a crucible steel, made without a crucible.  The charcoal itself becomes the crucible walls and the floor of the hearth its bottom.

 

So, can anyone help we decide on this question before i commit e-pen to e-paper about the different smithys my protagonist works in? many thanks

 

 

Quite the questions!  I've answered as well as I can at the moment in orange letters above, but you may also want to locate a copy of Williams's "The Knight and the Blast Furnace" from a library (they run ~$400 used).  He explains how furnace technology changed shortly after your chosen time period, including the introduction of cast iron and finery forges.  Your chosen period is the big question mark in steel metallurgy, though.  We know (pretty much) that earlier steel is almost always "natural" bloom steel.  We don't know exactly when pack carburization appears, but it's in there somewhere.  Seems like it was a very late Roman innovation?  At any rate, you picked the nastiest point in history to try and figure out exactly what was being done and why.  ;)

Try to narrow it down, and break the above into a few smaller questions so I'm not tempted to write a dissertation off the top of my head; I've got work to do! And I'm sure I'd miss a few key points, and have to go look them up, and darnit, there's that work thing again...

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Alan

Super! thanks for the clarifications there. I did read some of the bits on here about different bloomer processes but i was/am really not able to piece the subtleties together into one unifying theory that makes sense in a way i can present to a layman audience but that will also not cause rolled eyes for those who know more about it. its a delicate balance. apart from anything else, different sources do seem to directly conflict but that is the internet for you! The idea that fast and charcoal heavy vaguely = more steel and slow and lower ratio = more pure iron is a nice base to start from. its so hard to compare videos when people are describing their input as 'a bucket per whatsit' or talking about fine tuning the balance and reductions of various impurities that the Norse would have known nothing about in scientific terms.

I'm equal parts sad and relieved to know we don't really know what the answer is to this time period. to be more specific for context as to why i am looking so late in the viking era, the book is an alternate history where the Norse reject (violently) christianisation. its an exploration of what might have happened if the Nordic culture wasn't slowly subsumed in that way. so in my world, their ways of swordsmithing are retained for longer and merged with the advances in western blade design typified by the move from Oakshotte X to XI and XII. I would love to see what a XIa blade for example would look like if it was pattern welded and decorated/hilted by a Norse smith. so, thats what i am doing and why its so important i can believably piece together how exactly that would have been made. its a puzzle.

 

Interesting that my understanding of blister steel seems to be wrong. I thought the process saw repeated hammering and re-heating of the same piece to thicken the steel layer and i saw at least one source that said they would separate the steel from the base iron by hammering it till it cracked off. maybe I am confusing that with what you describe as the combining of multiple carburised pieces. 

 

The observation about bog ore is interesting. i was reading about that, fascinating that they can literally harvest iron from bogs and then after a generation re-harvest from the same place, like a sort of ultra slow growing crop. Either way, my fictional Norse smithy is based in Uppsala in the lowlands of Sweden and i believe that at the time they were already using the high-quality iron ore available in that region, or at least partly using it. i wonder if anyone know what process that ore is most suitable for? i suspect it would be suitable for straight bloomery steel? or perhaps they would have to then do a secondary process, surface hardening or hearth smelting. 

 

Hmmm. fascinating stuff. I think i am leaning towards my Norse smith in the swedish lowlands making pattern welded swords from carefully separated (by steel grade) parts of blooms and my germanic smith using more mass produced blister type steel. Although, maybe i will include the hearth process in there for the Norse smithy. i like it for its simplicity, the historical evidence of it being made in a very local, distributed way fits in with the story although i am not sure how valuable pattern welding is to hearth smelted steel. would it not be mostly decorative at that point? or does the hearth smelted steel still vary a lot and markedly improve from folding?

Edited by James Simonds

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