Although most of my readers will not see this, I've finally switched over to the 'new' version of Blogger. I was extremely resistant to this, as I have no use for so many of the 'services' provided from these Bill Gates style " My Blog" stet ups. I find them invasive and trivial at the least - and usually totally counter intuitive.
We shall see if this has proved a bad idea ...
For anyone internet / computer savvy enough, I have also turned ON the RRS FEED feature for Hammered out Bits. This is supposed to automatically notify a reader when a new post arrives on the blog. Mind you - you as a reader have to go into your e-mail account settings (likely on preferences) and plug in the URL address for Hammered out Bits.
I only vaguely understand this hoodo, my friend Neil walked me through it on a recent visit. It turns out NONE of the blogs I try to follow (only about a half dozen by friends) are set up to send out the automatic notices.
Anyway - if you can set up for the automatic RRS feed notice widget, it will keep you from having to poke in here to see if a post has been added
Darrell
Thursday, February 01, 2007
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?
No.
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...)
Darrell
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.
" 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?
No.
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...)
Darrell
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.
Darrell
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.
Darrell
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.
http://64.176.180.203/washtubforge.htm
"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!)
Darrell
* 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.
"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.
http://64.176.180.203/washtubforge.htm
"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!)
Darrell
* 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.
Subscribe to:
Posts (Atom)
Posts
