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Tim Mitchell

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Everything posted by Tim Mitchell

  1. Some smiths add graphite, some calculate as Jan mentioned and some use charcoal in layers with their iron which regulates the carbon content roughly itself. If you have a closed crucible you have a more accurate final carbon level as you will lose less out the top as gas. There is usually a bit of addition of carbon to the melt from any graphite in the crucible, but if you line it with a refractory wash that is also no longer a problem. Through calculation, especially if you use cast iron and purer iron with known carbon contents, you can get the melt accurate to plus or minus one point of a percent of carbon with no real trouble.
  2. Within reason the answer is yes. If you forge out a similar ingot with the same basic forging profile, you will usually get the same type of result. Every blade is that little bit different, but they will be similar in mechanical properties and appearance. Sometimes you just get that curve ball and we don't know why that happens, but most of the time the answer is yes. This is why I encourage the use of forging diagrams, so that a smith can reproduce and improve on the quality and appearance of the previous blade or ingot. Some would say that it does, and in my opinion it is not so much the pattern that contributes the qualities, but it is what causes that pattern to appear which makes the open watered patterns slightly better. It is to do with the microstructure of the pattern and how that effects the quality of the final steel blade in flexibility, edge holding ability and toughness. So the bands.... not so much, but what makes the high quality bold open watered bands, definitely helps to make a better blade. As far as carbon content, not many smiths can get a carbon test done. Most just calculate the precise final percentage from the known carbon content of their ingredients. There is another way which I have been thinking about, kind of a poor man's carbon test. It involves burying an insulated thermocouple inside a lump of your ingot or forged bar, and then raising the temperature of the furnace at a steady rate. where the critical points are in the steel you will get a little plateau in your temperature plot. These will show you where Acm is for this steel and consequently will give you a relatively accurate calculation of your carbon content when you compare it with the carbon iron phase diagram... If anyone does this before I do... please post how you went and show the plot!
  3. Well said Jan. Wootz is one of those things that keeps on pulling you back. I have a 1.6% C wootz knife which I have had for years and heavily used for all kinds of things, it has held up better than any of my stainless blades which have been my EDC for years, an SOG folder and a Ken Onion Leek. My wootz blades will beat them hands down for edge holding ability and toughness.
  4. The secondary arms of the dendrites are dissolved during an extended roast of an ingot. This leaves the primary trunks, but they are also in a more dissolved state. This makes the steel matrix stronger than it was previously. The brittleness of the steel matrix is a factor of the size of the carbides and the density of the clusters. Not all blades have dense large clusters of carbides and in a properly forged blade, you have a laminar structure of steel sheets with no visible carbides and of steel sheets containing carbides in scattered loose clusters of spherodized carbides, not the blocks of cementite that you would have seen in most modern wootz. When properly quenched and tempered, you get a blade with a nice perlite structure in the spine and body of the blade and at the very edge you get a hard tempered martinsite region. My personal opinion is that a wootz blade with a good open watered pattern will be just as good as a blade made from something like W1 with a tempered martinsite structure. Eventually we need to do some comparative testing of the different mechanical properties of a good section of wootz to show scientifically how it compares with other steels. Until then it is purely subjective. Naturally the carbon content of the steel is a factor, so we can't easily compare a 1.5% carbon wootz blade with say a really good 1095 blade. The less the carbon the tougher the blade... And we also have to compare structure with structure, it isn't fair to compare a bainite structure with a martinsite structure and say that the weakness is in the steel Wootz can have no pattern, there is actually a name for a Pulad blade which showed no pattern from ancient times in Persia. It is not the pattern which makes steel wootz or pulad, it is the type of steel, and it is hard to make generalisations about a quite diverse product.
  5. Thanks Jerrod for explaining your comment, I had a basic idea of what you were saying, but wanted you to really spell it out for the record. I agree with you for the most part and you are correct with the majority of wootz today. In most Wootz today the cementite is made from large globular carbide clusters and the dendritic structure is still largely intact. This is not the best state to have a blade in, if you are wanting to achieve sharpness, toughness and flexibility. The dendrites themselves actually don't exist in the ingot, it is the outline of the former dendrites which existed in the solidifying ingot which remain. The carbides of the Interdendritic regions are the weakness in the crucible steel ingot and blade, however some Wootz steel is converted through the process into a finer less brittle spherodized carbide structure and the "dendritic arms" have become homogenized back into the steel. This makes a blade that is much more like the modern high carbon steels. It is all in how the steel has been created that determines the final mechanical strengths or weaknesses.
  6. Any production line steel has a formula of how to treat it so that it turns out the best. Wootz does not have that yet... that is the problem.
  7. I am not saying that it isn't possible, frankly I know it is. But my point is to do with the repeat ability of producing wootz between makers. It all isn't made the same so the quality is a very individual thing as are the blades produced from it.
  8. Aha! but there are so many structures of wootz what structure do you think is not ideal? It is important to have a specific quality or structure to identify with your thought.
  9. Well, it is and it isn't. It depends entirely on the smith who made it and forged it out. The devil is in the details, and if you don't forge and heat treat it just right, you don't get that really flexible structure which makes it such a great material. It can be a very tough and sharp and durable material which outperforms some other modern steels.... if it is done right. Modern makers don't always know how to, or choose to, make their steel perform to the best that it can, and seeing the process isn't automated in a massive factory and the qualities come from subtle forging and heat treating, individual blades will outperform some other steels, and others will not.
  10. The modern carbon steel blades usually sit around the 0.8% to 1% carbon mark. Wootz is a high carbon steel and is similar to some tool steels sitting between 1% and 1.8% usually, there are exceptions but most were in this range. It makes very good tools, punches and dies and even chisels. The best of the wootz steels compare with a good high carbon tool steel such as perhaps W1 / W2 (0.7% - 1.5%C) or similar. They can take and hold a good edge, are tough when heat treated properly. The higher carbon range blades can also be close to that kind of steel if you heat treat it properly and you have the carbon segregated as an ideal spherodized carbide grouping. This means the matrix around the spherodized carbides is below 1% carbon and it makes a really good combination of hardness and flexibility, it is definitely unique and beautiful. You may be right about them not being able to identify specifically things like phosphorous, but they did know about various specific elements in their steel. But more specifically they knew the effects of adding some elements such as carbon, calcium, manganese, copper and chromium to their blades to deal with some of the weaknesses of their steel which were caused by Phosphorous or Sulphur. That is something that we know for sure from Archaeology and from historical accounts. So specific knowledge did exist, their explanations would be different than ours would be today, but they knew what they were doing and additions were very deliberate with a knowledge of the final result they wanted to achieve. The Hyderabad / Trichinopoly / Deccani process was one which as far as I know added nothing except two different types of iron. The Salem process also added nothing. This steel only contained elements which were from their respective ores and processes. This tells me that they had great confidence in the purity of their ore and product.. or just didn't care less . Adding ingredients added expense and usually would have been done to remove impurities. The goal usually was to make the steel as pure as possible, but there were occasions where some elements were added through deliberate alloying of other metals to achieve a specific material. They were much smarter than many today give them credit for. The Babylonians which the Persians come from were some of the oldest scientists on the planet. They taught the Egyptians who taught the Greeks who form the basis of our scientific understanding. We shouldn't think of them as primitive by any sense. Without their science we wouldn't have our modern steels today. I wouldn't say that wootz blades are made obsolete by the modern steels, but there are so many modern alloys which have similar or better characteristics that it is not cost effective or practical to use them for general tools that would suit Wootz. Considering Wootz sells for at least 1 euro per gram these days that is. I have a Wootz chisel which I made for doing some hardwood dovetailing on a jewelry box... I am a wood worker too . It performed comparably to any of my old high carbon chisels or my new Sandvik chisels. Perhaps even a little bit better at holding an edge. I was very impressed and if I had given a little more attention to quenching and tempering it would most certainly been better than my modern chisels. How I forge a blade of Wootz makes a big difference in the final edge stability and hardness. I have had blades with edges which were prone to chipping, and others which were really tough. It depended on the forging and the heat treating.
  11. Hi Vern, I thought I mentioned that briefly. The methods of quenching and tempering were various, and even without microstructural analysis it is possible to determine if a quench and temper method was a success or not. The changes were visible in the darkness of the pattern background and in the mechanical characteristics of the test piece much in the same way as today. Some smiths used an air quench, like Anossoff who used hot air from the furnace opening, or compressed air. This gives a fine pearlite structure. Others used a light oil quench from critical, which would create a combination of a pearlite blade with a marcasite edge where the blade is thinnest. It in effect gives a thickness quench. There were dung tempers and urine quenches, quenches with all sorts of weird and wonderful recipes some even claimed to make the steel non-magnetic after cooling, or to make a special background colour. Where there is marcasite on the blade, the pattern is partly obscured, but the best display of a blade pattern and flexibility of the final blade comes from the fine pearlite structure that Anossoff achieved through an air quench. It makes a very black background and it creates a very flexible blade especially if you have a fine grain structure and you have spherodized carbides, through proper forging technique. It is possible to determine the treatment of old blades by using hardness testing and by visual inspection under a microscope, of the crystal structure of the blade edge. It's edge holding ability also gives us an idea. There was no single process, just like everything else and everything contributes to the quality of the final blade. Finding a really high quality crucible steel blade was not so easy in the mid 1800s, Abbott said he had one exceptional blade which would out perform other blades in combat, but there are accounts of some quite important people in the battles of the day taking the sabers of the English and attaching them to their Talwar handles. It seems that the British blades were better and more consistent than the average wootz blades of India in that time and location.
  12. Ok, that makes sense now. It is amazing how little carbon it takes to make a big difference. When we think about it, the 0.5% difference of carbon is a tiny part (10g) of the final say 2 kilo ingot. I am lousy at spark testing, I just haven't had enough need to educate myself... I use materials with known amounts of carbon, it helps with getting my ingots consistent. But you have some good metal there, it is worth watering it down to get some really good ingots. What do you think your phosphorous level is in the ingots? Looking at the density of the dendritic pattern of the bar, I am guessing that you have a bit in there, there is plenty of white there. It may be the high carbon too, but I wouldn't be surprised if you have a healthy level of Phosphorous there too.
  13. Good to see you posting your efforts here Daniel. You are doing a great job and definitely on a fast track. I am curious about your carbon content still. As far as I remember, you didn't add any graphite or other carbon to your melt, is that correct? The carbon content is definitely up at least 2.2% from looking at the phase diagram... but unless you let it sit in the crucible for an age at melting temperature, the carbon has to be from your steel. Is it possible that you miscalculated the carbon content of your steel from your spark tests? The clay graphite crucibles can add a few points if you leave the melt at temperature for a long time, but I would be incredibly surprised to see that jump in carbon content coming from the crucibles... Just a thought...
  14. Thanks for pinning this Alan, I remember the old thread, it was good but we have learned quite a bit more since then and this is a little more complete I think. Coupled with the "Wootz Makers and Methods" thread, we have some good coverage on the subject. Although the makers and methods post could well be updated as it is almost exactly 3 years old a lot happens in three years...
  15. Really nice work Klaas! Congratulations, you have been paying attention! Those are some really nice tiny spheroids and lovely watering. Did you log the forging process that you used on a forging table? It helps you to be able to repeat the main elements of the process that got you that pattern. Keep up the good work mate.
  16. Ok, you are reading a little more into my comment than was intended. Steel itself is an alloy of iron and carbon, and a high carbon steel is from 1% to 2% carbon. That being said, the majority of the crucible steel examples out there fall between the 1.4% to 1.8% carbon range. Changing the carbon content makes harder blades, and it makes more carbon available for carbide patterning, so the higher carbon blades tend to have better patterning, no surprise there. Most steel contains trace elements as a result of it's production and ore source, but these trace elements are kept to a minimum as we can see from the analysis of the old blades. Some blades had higher manganese or copper or phosphorous etc, but there were not large amounts of alloying elements other than carbon added to the majority of the old blades. There are a couple of notable exceptions, but that is not what I am talking about. The different processes do add some to the trace elements, but the amounts of the trace elements haven't given us any major surprises, and the same sort of patterns have been made from steel with more or with less of specific trace elements and from different ingot creation processes. The goal of most smiths who make crucible steel today is to replicate the old steel to some degree, and to be able to match the performance of the best old blades through proper forging and heat treating technique. Proper technique ends up making specific patterns and so some patterns make blades with better characteristics than some other blades speaking generally. If we begin adding large alloying elements to crucible steel, other than carbon, which we have no historical foundation for, then we are venturing out into the field of standard steel production. Alloying began in the west with people trying to replicate crucible steel, and so if the purpose is to replicate what the ancients did, by adding large amounts of alloying elements we are possibly going astray. Not a bad direction, but just not a replication direction. We are seeking to get both better old patterns and better quality in the steel treatment, but most of the physical characteristics of the steel come from what you do to the ingot after it is made and not so much during production. Everything in the process affects the final outcome, but some things affect the final product, pattern or quality more than others. It is the forging technique that contributes more to the patterning and to the final qualities of the blade than anything else and it is this area of forging where we are trying to focus the most. Changing forging temperatures and technique and then examining the microstructural changes in the steel as a result. This is where most of the research is at the moment. We may find out later that some common trace element or some other addition to the ingot during the melt, such as tannin rich ingredients, contributes some very significant part to the final blade, and we know that little things can make big differences, but as for now there are no big surprises from the analysis of the steel. The current leaps in research are from forging temperature and ranges / technique.
  17. I wouldn't say that we have run into any major surprises. We have known for over a century about the effects of Sulphur and Phosphorous weakening the ingots, and about carbide forming elements such as manganese, vanadium etc. creating patterning in the ingots. We have known about the structures that carbon contributes to in the steel. This is all old stuff, however what has been poorly understood, and is still poorly understood, is the action of banding, what precisely causes the carbides to line up in the watered patterns. Verhoeven and Pendray were convinced that it was the presence of vanadium which allowed it but never worked out the mechanism. As far as creating a baseline, the question would be what the baseline was for, we know that adding specific elements causes slight changes in the contrast or boldness of the pattern, however what creates the different patterns is more related to the process and not the trace elements. This is proven by the fact that several different smiths are able to get the same type of patterns without adding anything extra to their steel and the composition of their steel is slightly different. They just use the same process. Composition is generally speaking (there I go generalizing ) not too important as far as the types of patterns which someone can achieve. The same categories of patterns have been obtained from different periods in history where the processes of the ingot production and the recipes were significantly different. Don't get me wrong, I don't have a problem with creating a baseline, I actually think it is a good idea. I wouldn't be surprised if some little changes are yet to surprise us. However testing is expensive and not practical for some smiths who sometimes struggle to buy crucibles... Not sure who may have done testing at different stages of their process.
  18. The problem with quoting Faraday etc is that they were accurate witnesses of the specific pieces of steel that they had in front of them, and in that perspective they were first hand witnesses... however, they were not reliable witnesses concerning their opinions of what the Indians were doing and how they were doing it. The first hand accounts of naturalists and travellers going through the regions and giving accounts of what was done at a specific location at a specific time is of utmost value. We do have to be able to see past the filter of the writer though and understand that sometimes the accounts are not saying what we think at first glance.
  19. I couldn't agree more, we have to test out what others are saying, just following the instructions doesn't give you the same result, there is technique involved. This is the hard part and it is what we are trying to work out ourselves through comparing our experiments with historical blades. Sometimes history is largely wrong, we just have to use skill in seeing through the parts which are fact and what is perception. It takes a certain type of person to be able to interpret the information and come up with that obscure truth from many different and seemingly unrelated bits of information. This is something you would fully understand.
  20. I agree that we could benefit from isotope analysis, X ray diffraction etc. However the chances of getting precise enough results from the blades in private and museum collections is very remote. X rays are just not good enough when we are talking about the trace amounts which would be the markers of the blades in question and museum pieces are not released for spark erosion analysis etc. I would suggest that there is no direct evidence of crucible steel production in Jordan, there are only possibilities. Evidence is finding a site of crucible steel production with broken crucibles, or a historical account of crucible steel being made there. We have none of that. The castle is not guarding the mine, it is a little distance away and it could have several reasons for being there. It may have been there to protect the source of iron ore, but the iron ore could simply have been used for wrought iron production. We know the site was an important source of iron ore, we know that there is a castle nearby, we know that the mine was used for a long time, that is all we know. Iron ore was mined and smelted all throughout areas where iron ore was located, however very few of those ore bodies were used for crucible steel production. We have to be careful to not to declare possibilities as evidence without direct physical evidence of production or accounts.
  21. This is so true, all we can do is keep learning and try to share the few pieces of the puzzle that we have. Often our knowledge is based on what other scholars have written and not on first hand accounts. As Ann Feuerbach says, you have to go back to first hand accounts if you want to be right about things. Reading what Faraday and the other English researchers from the early days said and taking it as gospel is a mistake which many people fall into. They misunderstood the processes and what they were actually looking at in many cases. The first hand accounts of the processes in India are the real gems which can help us to understand what was done, and why. I still have massive holes in my understanding. Most of my knowledge has been obtained from the last three years of research, not from making numbers of ingots in the preceding 12 years, but from intensive research and talking with as many smiths as I can. I found out what people were doing and why they were getting the patterns they were; adding that to my understanding in metallurgy. Just making ingots by a method or two doesn't give us any much further knowledge. We have to do research in lots of different areas, read and interpret the first hand accounts in relation to principles of metallurgy and be able to interpret and understand what we are looking at. The most important thing is for us to openly share what we have found out. Often what we are looking at is not what we think we are looking at and the reasons things are happening is not as we think. We never stop learning...
  22. If I understand you correctly Jan, what you are talking about is basically what is talked about on here as the Georgian Process, which is where the iron gets carburised by the charcoal and then falls down below the flux. It is a good way of controlling the percentage of carbon in the ingot in a very imprecise manner. However, once again we need to avoid saying "This is how they did it" because there is no "They" and there is no single process. We can't generalise about the old methods because there were quite a few. In that method they used the furnace temperature and the process to control it's own carbon content. In other methods they were very precise. Thankfully we have many crucible steel recipes and they all were specific weights and volumes of ingredients. Because of this we can see that for the existing recipes, time and effort and tweaking went into them. These people were not just making one ingot and hoping to get it right, they were making thousands of ingots and at that number it wouldn't take long to get the recipe tweaked for carbon content and to find out what worked well. We are told in history that the Indians invented the process but that the Persians perfected it and passed the method on to the Arabs. This is clearly seen by the primitive methods in deep southern India and Sri lanka which are small ingots with a very high failure rate, which were made of very approximate quantities of ingredients and interestingly enough didn't produce a pattern. Then we compare those primitive more purely Indian methods with the more Persian influenced methods of the more northern regions where multiple metals were used, very specific weights were used and the success rate of the ingots was high. These were the ingots which were associated with the Wootz blades and were traded internationally. So it seems that the Persians perfecting the process was actually correct. Many of the precise carburising recipes contained carbon donor ingredients which were very high in tannic acid and or gallic acid. These included pomegranate bark and hulls, oak gall, myrobalan, Cassia auriculata etc. The reason for this is not understood well, but it was clear that these carbon sources were specifically chosen for what they contained and that the ancient steel makers understood that the astringent quality of these ingredients helped the final product. This tells me that there was a migration of knowledge across Asia, a sharing of what should be used and why. Some recipes from Persia, where the iron ore sources contain significant sulphur, contain manganese which was added to help cleanse the molten steel from sulphur. Sulphur in the ingots wasn't desired as it lowered the forging temperature, causing them to be hot short, ie. crumbling at higher forging temperatures. Other recipes have calcium added in the form of shell, which as well as manganese helped to purify the melt of excess phosphorous which made an ingot cold short, ie. causing cracking when worked at colder temperatures and making the blade brittle in cold weather. We can see over time that the steel makers were learning and perfecting their recipes, seeking new ways to purify the ingots. There were reasons for everything which was added, some say that some ingredients were symbolic and that may be true, but when I look at the ingredients, the type of ingredients, I see that there is a very specific logic to why things were added and how much was added. The amounts were usually very precise, down to very small weights and measures. There was nothing random about the Persian influenced processes and due to the quantities of ingots which were made each year, and the time over which the processes were used, there was ample opportunity for perfecting the processes.
  23. 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.
  24. 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.
  25. This video of Al was really good and showed quite a bit of one of his processes that he had kept quiet about for some time. The roasting of the ingot at 1100°C for 30 hours enabled the secondary dendrites to diffuse which increases the banding spacing in the watered pattern. Also forging down from the 1050 - 1100°C range allowed the Carbide Forming Elements (CFEs) to move and line up into straighter lines forming the "Cluster Sheets". This higher temperature is needed to get the pattern to become less dendritic for this percent of carbon. The thermo-cycling helps to refine the grain structure after the long roasting time, as does going below critical temp (non-magnetic). This video didn't show the latter forging stage, but I would predict that once the bar got down to say 1/2 inch thickness he would have lowered his forging temperature to around 900°C ish and then forged down close to critical. This sperodizes the carbides and helps to strengthen the pattern. This process is slightly different in a few ways than the process that Al taught me back when I got started, and it shows elements of what he had learned over time about making the good watered Persian patterns. I have included a forging diagram for this video so you can see the temperature changes and the forging ranges that he used in this documentary. I have a full set of blank forging diagrams which I have made up for 1%C to 2%C if anyone wants copies to record their own wootz work, just let me know
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