Definitions and history of "Wootz" and such

[Vern Wimmer]

As a complete neophyte on the subject, but having a deep interest, I think an open discussion of the field surrounding the term "Wootz" including "crucible steel" "patterns".etc.

I know a bit about general historical research and applying it in the field. As an example, it once was part of my job to identify, or confirm prior identifications, of historical sites based on century-and-a-half-old documents and written accounts. How this relates here is that I had to learn a lot about original context and relative measure. What someone in 1852 who was on foot or horseback called "a mile" was not always, in fact rarely, what the odometer or modern maps call a "mile". In one case we had a gentleman who was completly immovable on a location because the military had measured it with great precision starting from the north bank of a river in 1853. His argument fell apart when it was pointed out that, in 1899, a storm caused the river's course to change almost 1/2 mile in the area the Army measured. So it seems with this topic to some who may have their own ideas. But we are lucky because we are the current practitioners of a craft that spans centuries, oceans, continents, and most divisions Man has invented. Let's take a good try at sharing what we have and come up with useful definitions and historical information for the benefit of the craft itself.

SO, what is "Wootz"?

[Tim Mitchell]

The question probably should be "What is crucible steel?", but anyway... 

Wootz was a steel that was also known as Indian steel in past history.  The original name wootz is an Anglicization of the word Ukku which means steel in one of the many dialects in India.  There are many other words to describe steel in India, but this one seemed to be the one that stuck in the west.  The word for the same steel in northern India and Persia was Pulad, also meaning steel and it's derivative in the baltic states was Bulat.  

Wootz / Pulad / Bulat was a crucible steel technology where ingredients were added to a crucible and a final ingot of steel was the result.  Some times the process was a decarburizing process, other times it was a reduction process or a carburizing process.  In one process it wasn't even in a crucible, but actually used the bloomery furnace as the crucible to make the cake of wootz, this was actually how one of the specimens which Joseph Banks sent to England was made.  It most likely came from the Salem district and still had pieces of crushed quartz embedded in the base of the ingot from the furnace floor. Joseph Banks called this steel wootz as well. 

Crucible steel known by the names Pulad, Bulat, Wootz was made over a wide area and each specific language region had their own name for it. With the exception of the steel from India which was traded all over Asia being called Indian Steel.  These steels were made in Mysore, Decanni, Salem and a few other places in India, it was also made under the name Pulad in Turkmenistan, the Fergana Valley, Chahak and other places in Persia. More places are being found periodically and many of the older sites have vanished to the point that we have little idea where it was made.

The earliest examples of crucible steel with carbide patterning is on blades from around the first century AD. Some say the first century, others say the third century, but it is around that period.  However there are textural references to Indian Steel or what we would call crucible steel back in the time of Alexander the Great and some claim it to be even earlier.

It is claimed that the process was invented by the Indians and then perfected by the Persians.  We must remember that the central Indian process at Decanni (Hyderabad) was actually overseen by the Persians and as I understand it, it was actually called Pulad by them.  The ingots from Mysore and from Decanni were exported out of India and into Persia where the trade was controlled or restricted to the west.  There are references to this trade as being massive in the 1600s and after.  This steel was used by smiths throughout Asia to produce the wide range of patterns which we see from that time onward.  There are many recipes from times predating this period, but it seems that after the 1600s most of the steel was produced in India and exported to smiths who made the specific patterns.  There was still some being made in Persia, but the sheer quantity was not to be compared to the export from India. 

There was variation in the process over time even at the same location, but generally the ingots were made in a ceramic kiln type furnace where multiple crucibles were placed.  The crucibles were raised to melting temperature over a long period of time (5 or more hours) and then sometimes allowed to cool outside the furnace and at other times allowed to cool in the furnace at a slower rate.  The slower the rate, the larger the dendrites and also the more likely porosity would be to develop in the center of the ingot.  The ingots were often then roasted for extended periods of time to soften them and this also helped to increase the width of banding in the ingots.

One important thing to say is that Wootz is often connected with the steel produced in deep Southern India and Sri Lanka, this steel was in the form of rods or long cylindrical ingots.  This steel never produced a significant pattern and the steel that we normally connect with being Wootz blades and Armor was in the form of cakes or bun shaped ingots.

[Alan Longmire]

A good definition, Tim!  A far more simplified one that I have used is "wootz is a crucible-made steel of high carbon content ( often 1%+) that has some kind of carbide forming element in the mix which, due to the process used, produces the distinctive alloy segregation bands we call "watering."  

After that it gets contentious.  Exactly what went into those crucibles is hotly debated, as is which carbide forming element and why (often vanadium, but not always).  Was it quenched? There are many many legends of what can and cannot be done to it heat-wise without losing the banding.  All of which were confused for me the day I saw a talwar blade that had been broken and forge-welded back together.  You could see the weld, and the discontinuity in the banding, but dogma has it if you get wootz that hot you lose the pattern completely!  On this blade it was as clear at the weld as it was elsewhere. Go figure, eh?

[Joshua States]

An excellent topic of conversation, and one I am keen to follow. Thank you Vern, for starting it.

So, what are the variables, or components, or requirements that cause the dendritic patterning? How does someone process the iron and be assured of creating the desired effect? Is it clear that the dendritic patterning was intended by early smiths, or was it a happy circumstance?

Edited December 9, 2017 by Joshua States

[Vern Wimmer]

7 hours ago, Tim Mitchell said:

The question probably should be "What is crucible steel?", but anyway... 

 

I thought about that and I had it in my first draft but there, to my eyes, doesn't seem to engender much discussion. "Crucible steel" is steel made in a crucible. You can divide it by "from ore" from "prior smelted iron" etc. But you have a hard time saying that steel that comes out of a crucible isn't "Crucible steel" OTOH when you use the term "Wootz"--Lucy, you got some 'splaining to do.

[Vern Wimmer]

OK, why are we concerned with the "dendritic pattern" ? 

Is it merely an attractive cosmetic pattern and is it the sole measure of "Wootz" ? 

Are there qualities, in application, that are desirable ?

[Tim Mitchell]

Hi Alan, you raise a good point about welding of wootz. It wasn't uncommon to forge weld crucible steel, we see repairs like you saw and we also see chevron style blades where alternating sections of pattern welded steel and Wootz were forge welded into one blade.  Al Pendray actually did this.  The truth is that because of the higher carbon content that is in most Wootz blades, you have a lower welding temperature than normal pattern welded steel.  You can raise a 1.5% Carbon Wootz blade with a good watered pattern up to 1100°C without losing the pattern.  I haven't personally welded Wootz, I haven't had the need, but it can be done and isn't too hard from what others tell me.  Using cast iron filings in the joint is supposed to help make the welding easier.

Now to patterning.... in all crucible steels, ie. steels which have been allowed to be solidified undisturbed in a crucible, dendrites form.  These dendrites are tree like structures of more pure iron which grow during the solidification process.  The slower the solidification rate, the larger the dendrites will be that are formed.  As the dendrites form, any Carbide Forming Elements such as manganese, vanadium and phosphorous are pushed into the spaces between the dendrites.  These areas are usually called the Inter-Dendritic Regions or IDR for short. When the ingot has fully solidified and cooled we then have only the microstructure of the IDR left as evidence of the dendrites, there actually are no longer any dendrites at this stage, it is all steel.  When we say that an ingot has a dendritic structure this is what is being referred to, it is this carbide shadow of the dendrites which gives the ingot it's pattern. This pattern is the foundation of the final pattern that we see on a finished crucible steel blade. But everything that is done to an ingot affects this pattern and can change how the finished pattern will display on the blade surface.

Most of the old ingots contained high levels of phosphorous and some levels of sulphur making them more temperature sensitive when forging.  The ancient makers often used to deal with this by roasting the ingots for long periods of time around their furnace which would remove carbides from the outside of the ingot making it easier to forge and less brittle.  This roasting process also annealed the ingot and started a process of evening out the carbide forming elements in the dendritic structure (the IDR).  This partly dissolved the branches of the "trees" and left more of the main trunks in the microstructure.  This had the side effect of increasing the width of the banding between the final patterning bands of the blade which was a highly desired quality.

Once the ingot was roasted enough it was then sold to merchants and the ingots made their way to the blade smiths.  The smiths would then forge the ingot out into a blade and precisely how they forged it out determined how the final pattern looked. If they forged the ingot out at a low temperature then the IDR would remain relatively intact and so you would see a stretched and crushed dendritic structure on the surface of the blade.  This is the most common form of pattern which we see today.  If they forged the ingot up closer to the Acm mark on the Iron Carbon Phase Diagram (they didn't have a phase diagram back then ) the IDR would break apart more and it would look less dendritic and more of a watery pattern. 

For a long time it was thought that the ancients didn't forge above the Acm mark significantly, but when we look at the account of Abbott in the Punjab, he describes a smith forging an ingot at what would be called a bright yellow heat today. This ingot was most likely one from the Salem region of India. So we know that some smiths did go that high and from those of us who regularly forge at these temperatures, we know that the lovely open watered patterns come from forging at these higher temperatures. The smiths didn't have any way of knowing what the carbon content was in the ingot they were forging and they only used their eye to determine the temperature of forging, so the way that they would have been able to tell the correct forging temperature for any one ingot regardless of the carbon content, would be to raise the temperature and hit the ingot with a solid blow and observe how much of a dint the hammer made. This is a foolproof way to determine the correct forging temperature for an educated eye, and it is the way that several smiths today believe that they did it.  The only way they could have done it.

Forging an ingot at this temperature range causes the bands of carbides in the grains to line up and the rough dendrite bands become straighter and orient according to the plane of forging.  We still have no idea as to how this happens although there are some theories.  But this super straight carbide sheet structure only forms after forging at high enough temperatures in the early stages of forging the ingot.

There are accounts of forging at lower temperatures, and certainly we see evidence of this with the purely dendritic patterns, and even the blades which were forged at higher heat to get the watered patterning were forged at lower heat in the latter stages, this is because we can see that the carbides are spherodized in the final blade surface.  This spherodization is evidence that the smith forged around the critical or non magnetic temperature of steel (727°C) forging down to below this temperature spherodizes the carbides and increases the flexibility and toughness of the blade.

There is another form of patterning which is often confused with the cluster sheet watered pattern, and this is the grain boundary pattern.  This looks very similar, but on closer examination it is round loops which have been stretched and squashed together to create the patterning.  This pattern comes from going slightly too high in forging and the carbides jump to the large grain boundaries.  As the temperature is lowered and the grain boundaries are refined at lower forging temperatures, the ghost of the old large grain structure remains and is stretched becoming more visible and it diffuses (spreads out) into the appearance of sheets. These are the basic three types of patterning mechanisms, dendritic, cluster sheets and grain boundary. All are beautiful in their own right and are original patterns, and they all tell us how the smith forged out the blade. Whoops... there is one more pattern and that is ferrite / perlite banding which happens to blades which are below 1% carbon content.

These patterns created the base for the main groups of patterning in the ancient blades.  The ancient smiths used to use chisels and punches to crate ladder patterns, rose patterns and also shaped hammers to undulate the pattern sheets in specific ways, just like we do today with pattern welded steel blades.

Some accounts claim that the smiths quenched the blades in oil, some (unlikely) claim a blood quench, others use an air quench.  There are quenches using urine and others which claim to make the final blade non-magnetic... so we can't say that Wootz / Pulad was quenched "this way".  There wasn't one way.  Quenching in Air makes a perlite structure in the blade which is flexible and tough, but with limited hardness of the edge in most cases.  Other quenches would create a combination of perlite and martinsite, which gives a good mix of hard edge and tough flexible blade.  Wootz / Pulad didn't have one level of quality just as there are really good and very average quality blades today.  The legendary qualities of the blades (probably exaggerated) came from the forging technique and then from the way it was quenched.  Abbot was, among other things, a collector of crucible steel blades and he categorised the different blades according to quality, saying some were exceptional and others were very poor, he claimed that the Sham from Syria was the absolute worst for quality. There is an account in existence of how to restore the pattern in a blade with a poor pattern and the quenching stage was a perfect description of a quench from precisely non-magnetic. The ancient smiths, the good ones that is, were not to far from our knowledge of the proper way to heat treat a blade.

 

 

Edited December 9, 2017 by Tim Mitchell

[Gary Mulkey]

Vern,

In my research I found that the carbide nanotubes were what gave the original  wootz its cutting ability as the rest of the blade steel was primarily pearlite.  I don't want to start a debate or step  on toes but that's what I have found.

[Tim Mitchell]

1 minute ago, Gary Mulkey said:

Vern,

In my research I found that the carbide nanotubes were what gave the original  wootz its cutting ability as the rest of the blade steel was primarily pearlite.  I don't want to start a debate or step  on toes but that's what I have found.

Some blades did contain carbon nanotubes and it has been a much hyped element of discussion in the topic of Wootz recently. However we have no idea how many blades from ancient times contained carbon nanotubes and what the connection was, if any, to the legendary performance of this steel.  It may have a bearing, and it may be more common, but that is no something that is known yet.  Just having a good crucible steel with no nanotubes would have flexibility and toughness depending on the crystalline structure and carbide shape.

[Joshua States]

Wow. A lot of info there. Thanks Tim for the elaboration on patterning and forging applications. Let's go back to the beginning for a moment and talk about process if we may. A smith would collect the raw materials required for production. Knowing where the earlier versions of this process occurred, what materials were available in those areas? Did that even matter, because materials could be brought in from virtually anywhere, even in ancient times. (the trade routes were far more established than one might think) Has anyone been able to determine the sources for these materials?

[Tim Mitchell]

Ok, back to the process... actually the processes as there are four distinct types of process that were used.  Most of the processes used bloomery iron which was either produced onsite or was made at other locations and bought by the crucible steel makers.  In India the caste system was very ingrained and there were people who only made different types of iron.  Some processes added wrought iron and cast iron together, others added a larger amount of carburising organic matter to wrought iron, there was also a reducing process, however the two most common methods were the carburising process and the method of using cast and wrought iron. 

Most of the old processes from Persia used wrought iron, and plant matter which was high in tannins was added to the ingredients, sometimes shell or manganese would be added to clean the metal of impurities.  This type of process would often result in an ingot in the high carbon steel range. 

Other processes would result in an ingot which had a higher carbon content and were more like cast iron.  These required a time of long roasting in the furnace to lower the carbon content to a place where it could be worked sufficiently into a blade.  Roasting of ingots served several purposes depending on how it was done.  It was used to reduce sulphur in the ingot, to reduce the carbon or simply to anneal the ingot, but that also had the added benefit in giving the final pattern a higher contrast with greater spacing between the bands of carbides.

Some ingredients would most certainly have been from the local area such as wood and sometimes iron, other more uncommon ingredients would have been bought from traders.  All locations that I know of obtained organic matter from the location where they had the furnaces.  Once the wood was used up they would have to move to another location.  Some were near ore supplies, and others were needing to have others make bloom iron and buy it in.  We have old accounts of towns which were well know production centers of bloom iron. 

In Salem, India the process that was used was to line the bloomery furnace floor with crushed quartz, then take the cast iron fragments of the bloomery process and melt them down into a molten mass of metal in this depression or massive crucible.  The furnace was then run until sufficient carbon was burnt out to cause the steel to solidify and they would then remove the ingot and cool it with sprinkling water over it.  This made a thin and rather wide ingot often with a shrinkage cavity in the middle and sometimes with quartz grains in the bottom of the ingot.

Notwithstanding the many differences, there are some significant similarities in the different processes.  Most of the processes required some form of organic carbon source and these were as far as I can tell, always very high in gallic acid and or tannic acid. The processes mostly used bloomery iron as an ingredient which contributed the phosphorous to the ingots, which most of the old ingots had in some level. The ore in Persia was high in iron sulphides which occurred as a white, yellow or greenish powdery seams on the iron ore deposits.  This required them to add manganese to the melt, to combine with the Sulphur to produce Manganese Sulphide which then separated out as a flux.  The ore deposits in India did not have this sulphur problem and so no Manganese was required to be added and the only trace minerals which were in the ingots were those from the ore, from the charcoal or the ingredients added to the crucible. Sometimes calcium in the form of shell was added to help to lower the phosphorous and silica content of the ingot through combining as Calcium Phosphate and Calcium Silicate which rose above the steel as slag.

All our modern steel making techniques and understanding began through the study of crucible steel and our alloying processes and steel purging methods sprang from these ancient methods.

 

Edited December 10, 2017 by Tim Mitchell

[Vern Wimmer]

So, if I understand correctly, there were processes that had to add carbon to the raw steel and others that removed carbon as well? 

It further seems apparent that there were several methods of "skinning the cat". It seems to me, and is probably more obvious than I realize , that we are looking at a method of ancient/old visual analysis indicating the characteristics of a given billet, bar, blade. If that is correct then, ironically, those folks almost had a system that was in some ways simpler, if not superior to ours today for understanding the characteristics of a piece of steel from a good look at it. How many of us can do that with unlabled steels today ?

 

Edited December 10, 2017 by Vern Wimmer

[Tim Mitchell]

There is evidence that they were able to look at the pattern of an ingot which had a window ground in the side and which had been lightly acid etched. They could tell how good the final pattern would be and perhaps the spacing of the pattern in the final blade.  They were used to using ingots from a specific source and so the ingots wouldn't have changed too much for a particular smith, but when they changed to a new supply of ingots they would have to be able to verify the correct temperature range to forge in for their new source of ingots.  It is part of being a master craftsman.  Now not all would have been able to do that, only a specific group who had been taught how to make the best quality blades.

The processes which added carbon did so to bloomery iron which would have been very low in carbon.  The reverse process removed carbon from cast iron which had a carbon content of over 2%.

[Vern Wimmer]

Is there a performance difference between the steels from the different methods - bloomery v cast ?

[Alan Longmire]

Some say wootz, because of the banding, will cut better even when supposedly dull.  But people say a lot of things.  Since it is a crucible product the carbon distribution is even and there are no slag inclusions, unlike bloom steel (Evenstad process possible excepted).  Therefore, in the right hands it is theoretically a "better" product.  Remember, the west rediscovered crucible steel when Huntsman needed a more uniform spring steel for the chronometer in the 1760s.  It was lower carbon and not processed to show the structure, though.

[Jan Ysselstein]

Alan,  Somewhere in the Pit Charcoal  thread I have a wootz knife showing on pages 5 and 6 . This knife looks good and has been sitting in the kitchen unsharpened for about two years ( for  show). I recently sharpened it and scraped the finish off my dining room table with it and then sharpened it and put it in use...due to arriving at a secondary bevel the etch is a little messed up....but does this thing cut ...I was surprised  .So even if the wootz thread I am working on produces nothing beautiful ( it will) I will have some really good steel for blades..

Edited December 10, 2017 by Jan Ysselstein

[Tim Mitchell]

There really isn't a difference in the quality of the steel from the different crucible steel processes, regardless of whether they carburised bloomery iron or decarburised cast iron, they all achieve a crucible steel between 1 and 2% carbon which is very pure and relatively free from inclusions.  The Indian steel was better in most cases because of the lack of sulphur and ease of forging. What makes more of a difference in the quality of the steel is how it is forged.  The strictly dendritic patterns have less diffusion of the carbide microstructure and can be a bit more brittle than a watered pattern.  The watered patterns have more diffusion, finer carbides and are generally speaking less brittle.

But the big part is to do with the final stage of forging.  If you forge down through the critical temp you will get the carbides spherodizing and this makes the biggest difference to toughness and flexibility.  If you do an air quench the blade will be very flexible but not as good at cutting as some other blades which have had a good oil quench.  It is horses for courses, do you want a blade that is designed to cut steel or do you want a blade that holds a very fine edge geometry and lasts a long time?  You can't have both, unlike the legends try to make out...  

Edited December 10, 2017 by Tim Mitchell

[Vern Wimmer]

Are there historical examples of the different "horses" as it were, through design or application, perhaps by region or culture ?

[Tim Mitchell]

No one has done a detailed study of the edge hardness and geometry of the old blades as far as I know.  Wootz / Pulad was used for scissors, kitchen knives, swords, armor, armour piercing daggers and punches etc. It was used for everything that we would use a tool steel for today. So yes there were different historical applications, but I know of no analysis of the steel characteristics in these different applications.

 

[Vern Wimmer]

I was thinking in terms of, say, Crusaders v Saladin's troops (since that has become a popular entertainment field). That, of course, opens the door for the area of "European" importation and application/use of Wootz and the differences between it and the European metals and their making and working.

[Tim Mitchell]

The Europeans didn't import Wootz as far as I am aware.  Huntsman's process took care of their needs for crucible steel and was very good in quality. There is evidence of crucible steel being worked in Scandinavia for a period of 200 years, this steel most likely came through the Vulga River trade route from Merv in Turkmenistan, a site which was active during that period.  Most of the stories about the crusaders and Salhadin were fiction, I have yet to see one that was actual history.  If anyone has accurate first hand accounts then please let me know.

[Zeb Camper]

52 minutes ago, Tim Mitchell said:

The Europeans didn't import Wootz as far as I am aware.  Huntsman's process took care of their needs for crucible steel and was very good in quality. There is evidence of crucible steel being worked in Scandinavia for a period of 200 years, this steel most likely came through the Vulga River trade route from Merv in Turkmenistan, a site which was active during that period.  Most of the stories about the crusaders and Salhadin were fiction, I have yet to see one that was actual history.  If anyone has accurate first hand accounts then please let me know.

Excuse my general ignorance, but the Scandinavian blades mentioned include +ULFBERT+ swords right? And was my spelling correct? I seem to recall an H somewhere.

You guys are doing a great job putting this thread together. Ought to write a book.

[Tim Mitchell]

Thanks Zeb, you are correct, the Ulfbert blades were the ones that were made from some kind of crucible steel.  There were many imitations over time with different spellings.  We still don't know where they were forged, it could have just as well have been somewhere in France or Germany, but they did end up being used by the Vikings and were very prized items of warfare.  There is a great doco which was done by Nova with Ric Furrer of Door County Forgeworks.  It talks about the swords and Ric made one for the film crew... actually 9 swords if I recall correctly he had to do all the different stages for a two day filming. 

 

[Vern Wimmer]

That was a terrific program on NOVA. It does bring up the question about different sword/weapon styles across different cultures and there is some hazy kind of "chicken or egg"  question about steel leading weapons development or vice versa . It really comes to mind when one sees the interest in the making Tamahagane and other Japanese varieties and that, of course, brings up the question of similarities and differences between Japanese crucible and Wootz.

[Viktor Johansson]

The Ulfberts are a cool mystery. The name is Franskish. The letters are roman not viking, and the cross is Christian. Yet most blades are found in pagan Scandinavia. most people seem to think the name refers to a Bishop. Bishops of these early christian germanic types were more like warlords. They did not do this "turn the other cheek" thing. Jesus was still a little bit like Tor.

If they were made from Asian/Indian crucible steel, the Vikings could have traded for it in Persia (or maybe Constantinople/Miklagård?) via the Volga river trade routes that leads to the Black sea or the Caspian sea depending on what route you choose.

There was a general trade ban between the Christian and the pagan worlds of Europe, especially for weapons. Yet this Ulfbert character (or brand) clearly is not Scandinavian or Viking. So could it be that some Frankish Bishop metallurgical god was doing foul business on the side? Or perhaps for some reason migrated to the pagan world and forged quite many crucible steel blades for the pagans?

Does anyone know what results metallurgical analysis of the genuine examples of Ulfbert swords gave? Are they similar to high quality persian or indian blades? We clearly have no pattern to look at because of corrosion. Does x-rays reveal bands of carbides? Could it be that the steel was produced somewhere in Europe? Could it be very very high quality bloomery? Some very early product of a blast furnace? Or more likely made from imported asian steel?

The oldest known blast furnace in Scandinavia is from Lapphyttan  and dated to about 1150, much too late for these Swords.

I have so many questions about this.