Tuesday, January 30, 2007

Blade Surfaces - Viking Age

Posted by Gus to Hammered out bits at 1/29/2007
" I have a question about finishes for historical knives. I really like bright shiny finishes, but what would the historical record say about shiny finishes. Is there a way to speculate on this from the historical record? "

Is there a way to examine artifacts and determine their original polishing level?


Since I know Gus, I suspect what he is referring to here are blades from the Viking Age. (This a continuation from yesterdays post and recent article, which yes, did not cover that aspect.)

Almost without exception, any blades still in existence from the early Middle Ages or pre-Conquest will be heavily corroded. Any iron based object tends to oxidize with time back into what is basically rust. The level of corrosion is typically quite high for Viking Age objects. So much that even information on exact measurements of the starting object is hard to determine. (As an aside, this should be taken into account when looking at descriptions on things like weights especially. What will be listed is the CURRENT weight - which may be quite different than what the object was when 'new'.)

Since the original surfaces are gone, we have to look at other things to determine what finish may have existed on the blades when they were produced.

As any blacksmiths know who may be reading this, it is unlikely that the original forged edges were taken down to much less than about 1 mm (say 1/32"). Although a talented smith might be able to forge thinner than this, doing so while maintaining an even straight line is so difficult as to be basically a waste of effort.
Any pitting on the surface of the blade would certainly be removed by grinding. Again depending on the skill of the smith, the number and size of these forging marks will vary. I know with my own work (some skill and higher temperature coal fires) I expect to remove at least something between .5 to 1 mm off each surface of a blade. Note that this combines with the degree of forging so that by the time I get the surface smooth, I've pretty much reduced the thickness at the edge to a sharp line. For purely functional reasons, we can expect any historic bladesmith to have also removed any forge marks. Any imperfection in the surface creates a potential weak spot where stress would become concentrated. A forge pit on a blade becomes a spot that may cause failure of the blade in use, either a crack or even the blade shattering across. So for this reason, you should expect a historic blade to be flat and clean on the surface.
A secondary check on this would be looking at the references to especially swords in the Sagas. Often there are descriptions of how blades 'flash in the sun' or otherwise brightly reflect light. A clear indication of the use of clean metal surfaces.

Next what we need to consider is the tools available for the work of that grinding. Just as pits can become potential break points, any deep grooves or scratches in the surface can do the same thing. (Note I'm not talking about fullers here, which run parallel to the cutting edge. Fullers reduce the metal volume while at the same time they create a more complex structural shape. These are added, particularly to sword blades to reduce the overall weight of the blade but at the same time maintaining the resistance to bending.)
Files are found in blacksmith's tool collections from the Viking Age. These are hand cut using a chisel, and are thus rough and irregular. Although they might prove of some value for the initial roughing out of the blade contour and surface, they really are too course a tool for actual polishing. Bare in mind that these historic files are made of metal with only a slight amount of carbon in it. In most cases they would be no harder than the metal in the blades themselves. Most polishing in this period is fact done with stones. Primarily what we find are hand stones, and relatively small ones at that. There is not way to think of the process of first flattening and then polishing a blade surface using hand stones except extremely tedious. I have seen a couple of narrow cylindrical grind stones from the period, mainly as fragments. These are all small and so likely equipped with simple hand cranks.
Any way you look at, the use of natural stones, moved by hand over the blade surface is going to put an upper limit on how fine a polished surface would be possible. We do know that good quality whetstones were a common trade item in the Viking Age. The ideal stone would have an even texture, and stones of differing grits ranging from course sandstone to fine shales are found. Through a long and careful process of working down through ever finer grits it is in fact possible to produce an extremely polished surface.
I doubt personally however that fine polished surfaces would have been the norm during the Viking Age. So much of the material culture of the Norse shows a stress on FUNCTION over mere form. Once you have reduced the rough forged surface of the blade to flat and without pits or scratches, there is little functional reason to polish any further.

I have a circa 1880 foot peddle grind stone tucked away in the shop. This was actually retrofitted at some point with an electric motor and pulley to drive it, though all the original peddle mechanism is still in place. This stone is roughly 2 1/2 feet in diameter and a bit over 2" wide (say about 75 cm x 5 cm wide) It hangs in a water trough in use. When I created one of the knives for the Norse Encampment program, I quite intentionally finished one side using this stone. On the opposite side I used modern tools - in this case the 6 x 24" belt sander with a 100 grit belt. It proved easier to maintain a perfectly flat surface with the belt sander and the cutting rate with the modern tool was a bit quicker. With a bit of care used on the large wheel however, the two surfaces are almost impossible to tell apart.

Taken altogether, my gut reaction is to guess that knives in the Viking Age would be in fact ground to be flat and clean - as is consistent with producing a high quality tool. The surfaces would be polished bright, but unlikely much beyond what would be seen with a contemporary 80 - 120 grit belt.

Now what happens to PATTERN WELDED blades is a whole other pail of fish. (And yes - I'm working up that article too...)


As a personal opinion, I stay away from highly polished surfaces on blades. The current trend to mirror polished surfaces is a reflection of 'knives as ornament' as opposed to 'knives as tools'. Although considerable care and skill (or the right expensive tools) is required to produce an even mirror finish, it is not desirable for a working tool. A mirrored blade is almost totally impossible to sharpen - a single swipe of an oilstone that is not absolutely correct scratches that surface and mars it. I consider all the knives I produce to be working tools and so normally only polish to 180 grit to produce a 'satin' finish.

Sunday, January 28, 2007

Knives from the Viking Age

Sorry to my regular readers for the gap since the last post. I had received several requests over the last two weeks for information (hopefully leading to orders) on knives in the Viking Age. This made me decide to put together another essay on the subject. This in addition to two earlier postings here that deal with some of the more practical aspects of this topic:

Wednesday, August 30, 2006
On Viking Age KNIVES

Friday, August 18, 2006
Considering a Knife

I set about putting together a more specific overview based on artifact finds from the period. The more I checked my reference works, the more I came to realize that there may not be a single overview that exists that looks at this subject. This started me compiling data from all the sources available to me, and one thing lead to another...

This is now appearing to be a major project, perhaps of some durable value. I have prepared a first stage article 'Knives from Coppergate' which focuses on the large sample (over 200) of knives excavated at York England. The link will take you to the initial report as installed on the Wareham Forge web site.

This article is destined to be included on the revised Version Two of my earlier 'Iron Smelting in the Viking Age' - which is the other main thing I have been working on over the last two weeks. More on that to come.


Saturday, January 13, 2007

On Trough Forges...

Posted by STAG to Hammered out bits at 1/08/2007

"At the 7 year's war rendevous at Fort La Presentation this last summer, the blacksmith used traditional "great" bellows, but a bit smaller than usual for ease of traveling. The forge was a wooden box, lined with clay. He burned coal, not charcoal.

"This is the simplest forge I have seen for making the long, narrow, knifemaking heat.

"This is designed specifically for charcoal, and varies in many respects from a normal forge. For one thing, there is a huge area below the air source. I would be interested in the physics of why this would be better than air from below.

A couple of things:

On historic forges:

The simplest forge is nothing more that a tube into a hole on the ground. I actually worked off a 'pit forge' for the first year or so when I started blacksmithing. I took an old cast iron hibatchi and set it into the ground for the fire box. A vacumn cleaner for the blower. Burning anthracite sweepings for the fuel (if you can believe it). A piece of rail track for the anvil.

at Heffenreffer Museum, Bristol RI, 2006
photo by Carolyn Taylor (off the DARC web site)

For Viking Age presentations I use a 'sand table' forge. Norse forges use a stone block with a whole about 2 or 3 inches up one face through which the air is pumped. The charcoal fuel is simply piled against this block. On the (speculative) reconstruction, seen above, a simple layer of sand about 3 inches deep contains the fire and protects the wooden planking of the table.

On the Lively knife making forge:

I think you are looking at the top photo on his web site - the actual metalwork details, rather than the middle photo - which shows the fire clay (adobe mix) in place. If you look at that middle photo you will see that the clay creates a slope sided containment which ends up exposing the top surface of the pipe. Rather a lot of clay used in this configuration - which has to make the whole thing darn heavy.

Direct from the Lively Forge website

This is a pretty standard arrangement for a what I've seen called a 'pipe forge' or a 'trough forge'. Reguardless of the name, the concept is to create a long thin fire through a series of smaller diameter holes running down the length of a section of tube. I have used a temporary arrangement in the distant past for the same purpose. I just dug a trench and lined it with fire brick laid down either side of the pipe. (These days I have a specially constructed propane forge with three burners in a line. This gives me effectively a 24' long firebox for heat treating swords or heating larger pieces for architectural work.)

Now I found one problem with the simple 'holes in a line' arrangement seen on the Lively forge can be seen in the image above (direct from his web site). You will notice that the fire is both largest and brightest at the blower end of the trough. In fact the amount of heat drops quite obviously towards the furthest half of the pipe tuyere.
The physics here is that the air pressure at hole one (closest to the blower) is at maximum from the blower. At hole two however, the available pressure is at blower minus whatever was pushed out of hole one. At hole three what is available is B-1-2, and so on at each hole in a progressive loss. By the time you get to about hole 4 there is hardly any air left to insert into the fire.
Ideally what you want to do is steadily INCREASE the diameter of each hole as you work down the series from the blower end onwards. A smarter guy than me could likely work the math here - its going to be some relationship between pipe volume and the area of all previous holes.

To be truthful, this forge set up is really just a waste of fuel. The only time you need to heat the ENTIRE length of a blade is when you are undertaking the heat treating, and only high temperatures are required for the hardening (heating and quenching) step.
In reality, any forge work on blades is limited not by available temperature, but on time of cooling against speed of hammering. In practice you can only shape over 4 - 6" in any given heat cycle before the metal is too cold to work. Remember that all historic sword smithing, reguardless of the culture or time, was done inside small diameter fires, by simply moving the metal through the fire as the work progressed.
You simply just do not need a long fire to forge knives. Even for medium blades or full length swords, you still only require a long fire for that single heat treating step *. If you forge a LOT of long blades, and do your own heat treatment, then it may be worth the time and materials to invest in a specialized forge for this process.

One other thing on the Lively illustration. It certainly appears that he is using charcoal BRIQUETS as the fuel. The lumps are the right size and shape - and far too regular in size to be natural hardwood charcoal. Although you CAN use briquettes, they are almost the worst choice I can imagine! The only thing they have going for them is wide availablity. Briquettes are formed from powdered clay soaked in used oil and charcoal dust. Thats why you get that heavy brownish ash from them, its the clay element. The heat will not be as even as natural charcoal, and there is a huge volume of ash and dust produced. The fuel lumps are also quite dense (heavier than properly coked coal). I suspect this leads to distortion of the metal as you try to thread it through the fuel mass. ( As you should be doing when heating metal, rather than simply laying the metal on top of the fire as I've seen so many beginners do!)


* You also heat the forged blade to past critical (red) for the first annealing step. However as this step involves a long gentle cooling period, it is not as important to have the entire length at exactly the same temperature. I find that I can easily heat a blade that is up to three times the length of the width of my coal fire by simply moving it back and forth while heating. In my case that works for blades up to about 18 - 20 inches long.

Saturday, January 06, 2007

Blacksmith Equipment 1775 - 1812

Robert wrote:

> Have a quick question for you to ponder. What is available as regards to
> Blacksmithing history? The time I am interested is around the American
> Revolutionary War Period say between 1775 and 1812. My wife and I have
> joined the Kings Royal Regiment of New York and they have need of some
> blacksmith work and this has led to the question above. My interest
> would be in the tools used and what the smith had available to him as
> regards a forge etc.

The answer to exactly what equipment would have been used by a given blacksmith in a specific period of history often depends on WHERE as much as WHEN. This is particularly true of the Settlement Era here in North America. (The principle applies to other eras as well.) Although you may not realize it, your specific reference (english / military / New York / 1775 - 1812) has a LOT of variables attached to it. These can drastically effect the equipment used by an individual blacksmith.

The majority of Settlers into 'the Colonies' would have been from the British Isles, and generally you should look to patterns used by blacksmiths there during the 1700's. Looking at what was common:
• Coal was the primary fuel.
• Air was directed into the * bottom * of the fire box. The fire box itself was set with some type of ash / clinker breaker at the bottom, with a T shaped fitting to pass this air while directing ash away past the flow.
• Bellows were of the 'Great Bellows' type. This is two large chambers set one on top of each other, hinged at one end. The lower bag was attached to the lever, with air from the lower bag being pushed into the second upper bag. This second bag would in turn be attached to the forge inlet tuyere.
• The normal set up for an English bellows is for the bellows to be set on the floor with the outlet pipe to be short and straight into the tuyere. The operating lever is set high, attached by a length of chain to the lower bellows plate. It hangs around head high, so as to be moved with the left hand.
• The standard blacksmith's shop was as a large, permanent facility. Typically the frame of the forge was made of brick or stone, with a similarly constructed chimney.
• Anvils of this time period are * just starting * to assume the shape that we consider the traditional form.
In 1750 an anvil is most likely to be a rectangular block, either with no horn at all or at best a very small one. This horn is sometimes mounted to the front side of the anvil, rather than the left end as came to be standard latter. Without a horn, curves were created by using a second forming surface, a large T shaped 'stake anvil'.
By 1810 - 20, the introduction of steam power is resulting in a drastic change in the mechanics of forming anvils. The much heavier steam hammers allowed ever larger masses of metal to be formed. Anvils will first adopt the pattern we are familiar with today - a horn and tail drawn (or welded to) a rectangular body. With passing years and ever heavier powered hammers, the horn especially will come to be more slender. ( This in fact is a rough guide for judging the age of an anvil - the chunkier the body the earlier it is likely to be.)

So the first variable from this initial description will be the influence of LOCATION.

Coal is widely available in all of the United Kingdom. Not only just coal, but the wide range of both grades and qualities of coal suited for specific applications. Ideal blacksmithing coal is softer bituminous coal, hopefully with as low a sulphur content as possible. Hard anthracite coal is great for steam engines or home heating, but not really useful in the forge.
The situation in North America is quite different. By the mid 1750's, coal had been discovered in both the 13 Colonies and the Canadas, transportation was extremely difficult. So much so that coal used in forges here was more likely to be transported from England via ship than dug on this side of the Atlantic. This of course means that only areas with easy water transport are likely to have any access to blacksmithing coal.
Fortunately for the growing colonies, there was a more ancient fuel available in abundance, charcoal. Charcoal can be made 'easily' (at the expense of labour) any place there were trees. A supply of wood was hardly a problem, especially into the interior (and farther away from the transportation network). It should be realized however, that the English trained blacksmith had been using coal as the primary fuel since about the 1400's. A charcoal forge works quite differently than a coal one, in terms of how it heats and how it effects the metal. One large difference is that a charcoal forge is most commonly set up with a SIDE blast of air. Typically the tuyere is positioned 2 - 4" above the bottom of the fire pot, to prevent the accumulation of ash from blocking the air flow.

(As a side note here, you can often see the mark of the charcoal forge on Settlement Era forge work. A typical charcoal forge heats only 4" of metal length, where in coal a heat of 6" or more is standard. Often twisted bars will show this distinctive short heat zone.)

Now the next variable to influence our hypothetical historic blacksmith is the description as being involved with the MILITARY, and the English Army specifically.

A blacksmith directly attached to the Royal Army would have access to imported coal. Supplies of proper smiting coal would have been shipped in with all the rest of the support materials for the unit.
Most importantly, a military blacksmith, especially one working 'on campaign' during a war, would be utilizing a MOBILE forge set up. During the War of 1812 (for which I have seen better references) there was a normal piece of equipment used by these traveling military blacksmiths. An old to wheeled ammunition cart was converted into a purpose built forge. The bellows was slung under the frame (more to the tongue end). Back between the wheels, either a metal basket or a frame to hold some bricks supported the actual fire pot itself. The small anvil and stub would be set on the wagon frame to transport, otherwise set on the ground close at hand to the forge in use. A good reproduction of such a rig, researched and build by Lloyd Johnson, is at Historic Fort York in downtown Toronto.

I have seen another interpretation of a mobile forge, this one built by a Virginian blacksmith/re-enactor ( Military Through the Ages at Jamestown Historic Settlement in Virginia). The fellow described the forge as being based on early American Colonial types. There the whole unit was roughly cube shaped, with two removable light cart wheels and pair of pushing handles. The bellows was an accordion style that fit under the lower part of the frame. The fire box sat directly above this, a fairly simple box of fire brick inside the wooden frame. The forge was more suitable for light work or repair - but this is the type of work most common to the military blacksmith on campaign anyway. The smith told me he was able to use either charcoal or coal with the setup.

One thing I should mention to those concerned with historical accuracy:
The small bowl furnaces with attached rotary blowers are definitely NOT CORRECT for anything before the American Civil War. The first of these units was introduced into the 1870's. If you can find one with the lever and ratchet mechanism, these are the oldest type. (Although I will tell you this is my * least * favorite system - of any historic type!). A bowl forge with a straight rotary hand cranked blower is closer to the 1880's or latter. The heavy rectangular table forges with large rotary blower even later still.

What you have here first a problem with survival of the historical samples. The type of traveling forges used by military blacksmiths' during the Revolutionary War and the War of 1812 were of necessity of wooden construction. The pairing of wood frames and forge temperatures is a bad mix for durability! As well these were deliberately 'temporary' pieces of equipment, never intended for long term use. They were easily cast aside, and the intervening two centuries has meant few have survived.

Any re-enactor concerned with strict authenticity is facing a serious undertaking if they wish to research and construct the correct replica equipment that would have been actually used by a late 1700's military blacksmith.

Monday, January 01, 2007

Comments - Iron Raven

If you check the comment left on my last entry, you will see something from Bill Flemming. Bill is being a bit shy too - check:

I had known that there had been a local smith 'on site' during the construction of the Outlander 'viking village' set. Bill is the man!

For those wondering what Bill is talking about latter, I took a team from DARC to the Canadian national blacksmiths conference CANIRON V, which took place at Annapolis Royal NS just before Labour Day in 2005. We mounted a demonstration iron smelt using all Viking Age tools. One feature of that smelt was the use of a theoretical solution to an air delivery problem . Team member Kevin Jarbeau had constructed an extremely large version of what is considered the standard Norse double bellows. For the CANIRON demo, it was only our second use of this equipment. As with the first attempt with it, the smelt suffered a major air flow problem and resulting crash in temperatures about two hours into the sequence.

Our CANIRON host, Brad Allen, had tore off and ran back with a mile of electrical cord and this motor powered blower. This allowed us to swap out the historic bellows and get the smelt temperature back before the whole furnace froze up solid. I never did know who had loaned us the blower in al the confusion.

So thanks for the loan Bill!


For readers who wanted some more background on this particular sequence of 'all Norse' smelts:
First attempt and demo rehearsal (June 2005)
CANIRON demo attempt (August 2005)
Bonfield demo attempt (September 2006)
Check under the archive of this BLOG for:
Wednesday, September 06, 2006
Viking Age Smelt - September 2

To date we have not gotten this large bellows to perform correctly. For two 2005 smelts, we had to switch over to electric blowers at about the 2 hour mark. In June we did get a very nice VA styled bloom at about 7 lbs. The CANIRON smelt produced an unweighed lump of cast iron (latter stolen - but thats another story!).
At the Bonfield smelt we were able (just barely) to employ the 'UbberBellows' for the entire sequence. Again the smelt product was cast iron.

For the first two smelts, the problem was with the internal valving system (or lack thereof) in the bellows. For the last smelt, at least a partial fix of the valves had been been made. At the Bonfield smelt, we allowed as many members of the crowd watching to take at hand at the bellows. In the end the variation in operators, coupled with a basic weakness in construction, resulted in breakage at the bellows hinges.

There is a discussion of WHY the 'UbberBellows' approach is being tested experimentally as part of my paper 'Adventures in Early Iron Smelting'. A version of the paper is available with illustrations ; HERE

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

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