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Tim Mitchell

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Everything posted by Tim Mitchell

  1. Gary, there were many sizes of ingots depending on the different uses and also the process used and the location.... and the century. Some ingots were round flat loaves, others were egg shaped, others were as you describe (from Hyderabad). The crucibles were sometimes fully closed and sealed, other times they had a hole in the lid to insert a rod, and other times there was no crucible at all (a bloomery furnace floor melt). The furnaces were in some cases open, heating the crucibles from below, some cases closed fully as you describe (at Merv) and some times able to be uncovered, checked and covered once again such as was used at Hyderabad in their round the clock process. It was there that they needed to know if the crucibles were ready to remove because of the cyclical process. As you can see, there were many different processes used in many different locations over a time period of close to 2000 years. Some crucibles were shaken, others were not but the final product was not controlled by the shaking, it was just a monitoring method. Much has been written on the web by misinformed individuals and some hold the understanding, incorrectly, that there was one "Wootz Process" which there was not. The only things that were consistent between all the Pulad/Bulat/Wootz processes was that a high carbon steel was produced and solidified into an ingot through medium to slow cooling and the resulting ingot was forged out into blades, tools or other useful items. Some ingots did not produce patterning due to insufficient dendritic structure in the ingot (through quick solidification), through incorrect forging temperatures, or through the ingots being so small that there was not enough reduction of thickness in the ingot to make the pattern visible. The ingots from southern India and Sri Lanka didn't produce a watered pattern as the ingots were rod like and too small in diameter, they were made into scissors, punches etc. There are few true researchers in this field and even some of the historical information can not be relied upon 100%. First hand accounts are the only accounts which are significant and what people said of the ingots in the past may or may not be true. It is a difficult task to weed out the facts from hearsay and rumour. Cheers, Tim.
  2. Hey Al, Your thoughts are good ones, but none of the things that you are asking about would make any difference to the patterning. The shaking of the crucible would be simply to hear if there were any clacking from metal pieces which were not fully melted. A crucible that was ready would have a fully melted charge and shaking the charge would in a similar way to getting bubbles out of concrete, cause some settling of the charge. However it would still need to sit long enough after the shake or there would be a risk of having slag inside the ingot after it solidified. The internal microstructure and microsegregation only begins to form once the ingot starts to solidify and the dendrites start to grow from the outside in. They will always grow from the same place and only the cooling rate will control the size of the resulting dendrites. The dendrites are the core building block of the patterns that are formed, without them there is no pattern it is that simple. It is what happens during the speed of solidification (size of dendrites) and the roasting period (dissolving secondary dendrites and increasing spacing of banding) and the subsequent forging temperatures (controls carbide shape and cluster sheet structure) which causes differences in the patterning. All of these patterning factors occur after solidification and are totally unaffected by the shaking of the ingot charge. One other thing that controls the way the pattern ends up is the proportion of reduction in the thickness of the ingot. Larger ingots have a higher degree of reduction than smaller ingots. This could explain some of the differing pattern characteristics through different centuries. Abbott drew a pancake style ingot that was forged edge on, this would have been about 5 inches in diameter and was from a different process which was used in the Salem district, melting steel prills in the floor of a bloomery furnace. Not all Wootz was crucible steel... unless you consider a quartz grit covered bloomery furnace floor to be a crucible, which technically it is. These are the same pancake style ingots which Joseph Banks received with the cone style ingots, all of which came from southern India. The ingots from Hyderabad area went to Persia and were not examined by the early scientists in Europe. The ingots from India, described in the 16th to 18th centuries were not the ones that we think of from Hyderabad/Deccani, or the Persian egg shaped ingots, but they are the pancake, buns of steel which were described to be like the size and appearance of a penny loaf. Penny loaves were round flat and about 5 inches in diameter. Other patterning differences can come from the use of shaped hammers and different forging techniques even if it may not be immediately visible to the average observer. Also the different trace minerals which are in the ingots can make a difference in the way the pattern displays, contrast etc. Hope that helps and good luck with your steel making, I look forward to seeing what you come up with! Tim.
  3. Really nice pattern Niko!! It is awesome when you get that consistency down and you can choose what pattern you want to make each and every time. I love that blade shape too, really nice. I can't wait to see what the finished blade looks like. Keep up the good work!
  4. LOL Yes...All patterns are repeatable it is just a matter of knowing how... It will be good to hear eventually what that method is. It will be helpful in the learning of many smiths. Niko does some really nice patterns and I am really happy for him that he is getting consistency now.
  5. Very nice fine spherodized groupings Niko! You have a very nice pattern there. Good work!
  6. KONASANDRUM PROCESS AKA DECCANI PROCESS: (1820-1823) from repeated visits and inspection of the process by Voysey. "Native manufacture of Steel in Southern India" - Journal of the asiatic society no.6 june 1832 p 245 [Extracted from the Journals of the late Dr. Voysey] "The granitic clay of the furnace is highly infusible; it is found in the neighbourhood, and is formed of the decomposition of granite rock with small pieces of quartz and felspar, and is so valued for its refractory qualities, that it is exported for the manufacture of crucibles, &c. In making the crucibles, the granitic clay above described is ground to a fine powder along with the fragments of old furnaces and crucibles, and the whole kneaded together with the chaff of rice and oil. The vessels are defended by a luting of the same, they are covered with a similar top, but a perforation is made in the latter. No char- coal is put into the crucible, but small pieces of kanch, or the glass formed in the process, are put at the bottom of them along with the ore, and serve of course as a flux. The crucibles are arranged and steadied in the furnace occasionally by the superintendent, with a long and stout rod of iron. The materials used in the preparation of the steel are two different kinds of iron; one from Mirtpalli the other from Kondapur, in the proportion of three parts of the former to two of the latter. The Mirtpalli iron is derived originally from the iron sand already noticed, and is sent in the state of large amorphous masses of a redish grey color, and of an extremely porous texture. The internal fracture is often iridescent. The Kondapur iron is procured from an ore found amongst the iron clay, at a place about 20 miles distant. It is said to be of a dirty brown colour, and very frangible. The Iron however, is moderately compact and of a brilliant white fracture. Occasionally it contains some ingredient which spoils the steel, render- ing it excessively brittle : the natives assert that the adulteration is copper, but it is more probably arsenic. The mixture being put into the crucible, the fire is excited and kept up for 24 hours. It is then allowed to subside, arid the crucible is taken out and placed on the ground to cool. When quite cold it is opened,and a cake of steel of great hardness is found, weighing- on an average about a pound and a half. The cake is covered with clay, and annealed in the furnace for 12 or 16 hours. It is then taken out and cooled, and again annealed, and this may be repeated a third or fourth time until the metal is rendered sufficiently soft to be worked. The steel is known by the name of Wootz in Telinga, and a Kurs, a cake of about 110 rupees weight, is sold on the spot for 8 annas. The daily produce of a furnace is about 50 seers, or in value 37 rupees. The cost of this steel is much enhanced by the exaction of the Jaghirdar who not infrequently appropriates the advance to himself, and leaves the purchaser still to incur the whole expense. The export, however, of the metal to Persia must be profitable, as it is sufficient to bring dealers from that country and to defray the cost and risk of traveling. We found at the village, in 1820, Haji Hosyn, from Ispahan, engaged in the speculation ; and it must have answered his purpose, as he was here again in 1823, having returned in the interval to Persia and disposed of the venture. He informed us that the place and the process are both familiar to the Persians, and that they have attempted to imitate the latter without success. Besides residing at the village, whilst making his purchases, he bore a personal part in the operation, weighing the proportions of the iron, and toughness of the steel himself."
  7. Here are some observations that I have compiled from different accounts over the last 350 years concerning the ingots which were sold to Persia for the making of Damascus Swords. Observations of the steel cakes from Golconda, (Hyderabad, Deccani, Konasandrum): The Golconda process was a carburising process where cast iron was added to iron with a lower carbon content. 1675 Tavernier: - The steel from Golconda is the only steel which will take a Damascene pattern. - The steel buns were in the past mostly sent to Damascus when trading went from India to Cairo through the Red Sea. - The steel cakes were sold to Persia and the Punjab for the making of blades from Hyderabad (editors note) - The Persians know how to Damascene with a sulfate etch. They can’t do it with their own steel. - The cakes of steel are large, the size of a Penny Loaf () and are cut in two. - Each half makes a sword. - These buns of steel are made in Hyderabad in the kingdom of Golconda (Deccan) and reported to be the best from the villages of Nirmal and Indore (editors note) Scott 1795: - “The specimens of Wootz were in the shape of a round cake of about 5 inches in diameter, and one thick; each of which weighed more than 2lb. The cake had been cut almost quite through, so as to nearly divide it into 2 equal parts. It was externally of a dull black colour; the surface smooth; the cut part was also smooth, and excepting a few pinny places and small holes, the texture appeared to be uniform.” Muchet 1805: - one of the cakes had two cuts in it cutting it almost in two so it was easy to break and see the quality of the steel in the middle broken section. He interpreted them as the result of crystalization, but also declared they could be cuts. These were the ingots which Holland declared were the ones made in Salem by the bloom process as they had occlusions of rust in some of the underside portions. Abbott 1856: - mentioned by Abbott in the Punjab Goorjrat, a 2 lb ingot which was lenticular in shape, was forged out into a bar in about 2 hours by the smith at a white heat (red heat according to edited version) This was available to be bought in Deli. (The old white heat seems to have been our bright yellow or yellow and the old red heat was our dark to mid orange. In the old days they went straight from red heat to white heat when describing temperature) - This ingot was not partly cut in half but was complete. - Dimensions were loaf like and about 5 inches in diameter and about 1 inch thick. - Were available in both large and small ingots. TL Lowe: - examination of the remains of crucibles from Hyderabad region Konasandrum, shows crucibles from 1 inch to 5 inches interior diameter. The 5 inch diameter ingots are the ones which the above reports are mentioning. NOTES: - It seems that there was a mixing of ingots, some from Salem and some from Hyderabad, arriving in Bombay and this accounts for the ingots which were clearly made from separate processes which both Joseph Banks obtained and which Smith sent to the royal society. Some ingots had oxide remains in pits on the underside as described by Muchet, and these were actually from Salem further to the south according to Holland's account in the 1890s. - It seems that the almost cutting in half of the ingots was stopped somewhere between the late 1700s and the mid 1800s. Although it was clearly a long standing practice. - Tavernier said that the Persian steel, although very good, did not produce the Damascene process. We know that in earlier times the steel from Persia did in fact produce patterns. However it is possible that in the later years the steel from India was found to be superior and replaced the steel from Persia. We know that Persia used large quantities of the steel from Hyderabad.
  8. The refractory clay which was used for the process in Hyderabad was a granitic clay which was high in quartz and in feldspar, it was exported as a highly refractory clay specifically for crucible use. If you make your own crucibles make sure you go either very high silica content (add lots of silica and quartz grog) or make it very high in alumina content. Try to cut it with pure silica or alumina to reduce the content of fluxing ingredients in the clay. You can also add wheat chaff from the feed store if you want to, it will help to make a more refractory crucible. Prefiring the crucibles is also a must if you aren't using a charcoal fire and slowly raising the temperature. The process at Hyderabad took 24 hours so the crucibles were being prefired during the melt ramp up. Using an unfired crucible in a gas furnace is not an option. It will explode... been there done that and had lots of flaky chips of ceramic dancing around in the furnace. It is a real bear to clean out too.
  9. I was asked about historical recipes for wootz and if we could add some to the thread. This first one that I am adding is the process from the Mysore region of India. It is important, in that it is one of the processes which is associated by many to be how they made the blades which we term Damascus blades or Wootz blades.... Some of these ingots were not used for producing blades, there were also variations of the process as will be seen from the excerpt that I include below. I was going to post it in the form of a summary, however I think it is better if the whole account is read to show how the processes in this one area were similar but also different. I have a copy of Buchannan's personal published account, but it differs so much from this account here that I really don't know what to make of it. Perhaps this was from a personal diary or a separate published account I don't have a copy of. Anyway the accounts here are more precise. This article excerpt was written in 1864 with the accounts going back to 1800. Southern Indian Wootz Accounts C1807.pdf
  10. Not quite Daniel, I have always used a 16lb hammer one handed to forge 2kg ingots, it does take awhile and probably longer than some have patience for, but it works fine. If you get impatient, rope a friend in as a striker, it makes a real big difference! As far as crucibles, for a 2 kg ingot you will need around a #6 bilge sided crucible. You can make a crucible which is taller and slightly narrower if you so desire, which will make a more egg shaped ingot.
  11. The problem with doing very small volume runs is that the smaller ingots don't get the same sheet like structure that the 1 - 2 kg ingots get. Thickness reduction is key to lining up the sheets of carbides, the greater the reduction in thickness, the better the sheets line up. You can get a bit of a dendritic pattern in a small ingot, but to get the watered patterning it is not the same.
  12. From what I have seen of the crucibles which have been made in old times, they used a ball clay which was low in impurities (fluxing elements such as iron oxide or potassium etc.) They often added a grog to the clay to help keep the crucibles from shrinking. This grog was quartz or old crucibles which were crushed to coarse grit. Water is a big issue with the crucibles, and you have to dry them out really well or fire them very slowly to stop them from exploding. Those who used water in their crucible construction in the desert regions air dried them and then would have done a slow firing. Those who were in the tropics such as the Indian processes, used rice husks in their clay and mixed up the crucibles with oil so that they didn't explode when heated. The process in some parts of India was a round the clock process and they would have needed a way of having an air/sun dried crucible which could be placed in a furnace that wasn't cold and still have no cracking. Some modern smiths use a red fire clay mixture and it seems to work well for them, just remember that the lower the carbon content you have in the ingot, the higher the temperature and the more likely the crucible is to fail. It would be good for other smiths to share how they make crucibles. I have made crucibles out of cast refractory cement and they work well except they don't like any fluxing ingredients in your melt
  13. Vern, forget the charcoal, use a gas furnace and forge, and use clay graphite crucibles. You won't have the problem with the rain then and you can still play with crucible steel.. As far as quenching, you need to quench from critical temperature (A1, non-magnetic) into heated, thin oil for general use. This will give an edge of marcasite and a body of perlite. You can also do a hot air blast quench which will give a fine pearlite structure but not as hard an edge. I have also heard of using a slicing partial quench through water and then allowing it to cool the rest of the way in air for use with wootz razors. This ends up with a bainite like structure apparently. The reason for heating the oil is that if it is not heated, the oil doesn't move away from the hot blade fast enough to give you a proper quench and the edge will not harden properly. Don't use water or the steel will crack, it doesn't like the sudden shock. Tempering is the same as any other carbon steel and multiple tempers seem to be a good thing. You have to be careful when doing your heat before quenching, that you keep your furnace at least a neutral atmosphere or it will pull too many carbides out of the surface of the blade and you will have to sand off too much of the blade surface to reach the surface pattern again.
  14. Banding is a phenomenon that occurs as a result of having specific carbide forming elements which become microsegregated only in the regions between the dendrites as the steel ingot solidifies. The dendrites are basically purer iron (0.7%C) Christmas tree like crystals which grow out into the cooling liquid metal. As the dendritic crystals grow out into the cooling liquid, they push the impurities into the spaces between them and segregate these impurities into groups of lines going different directions. This is called microsegregation, and when you look at an ingot you see lines of carbides which outline where the dendrites used to be. Now as you forge the ingot down and reduce it's proportional thickness, you see that there is a squashing of these IDR (inter-dendritic-regions) and they begin to form rough lines, which are more angled lines than straight lines. This is the beginning of the forming of the planar banding or as some call them, cluster sheets. When you have Vanadium, Molybdenum, Chromium or Nobium or other unknown Carbide Forming Elements (CFEs) the carbon is specifically attracted to these CFEs and they form in lines of Vanadium Carbides or Molybdenum Carbides etc. in the IDR which create the banding effect which we see in the final crucible steel blade. Some CFEs attract carbon in a stronger way than other CFEs. Those which attract the most carbon cause the highest concentration of carbides in the IDR and therefore they create the strongest banding in the final blade. The strange thing that no one can explain is how these slightly angled IDR sections come to be lined up in precise straight lines. It seems that when you forge the steel above Acm these sections of IDR somehow line up individually into larger straight lines. If it was just the IDR being squashed you would still see shallow angles in the cross section of the blade. However, when forged at the correct temperature range, these lines straighten out and the angles seem to disappear. Elements of what is going on is understood, but this effect is as yet without explanation.
  15. Ok Vern, sorry for not going into more detail. Agr and Acm refer to lines on the Iron Carbon phase diagram, most diagrams show Acm but few show Agr. The phase diagram shows the changes of state and crystal structure of iron as the carbon content of the iron increases. When you look at a phase diagram you see a horizontal line across the lower quarter of the diagram. This is at around 727°C which is called A1, critical temperature, non magnetic and also Curie temperature. The temperatures change slightly from diagram to diagram, but the line represents the place where these all exist. Now when you look at the diagram you will see at around 0.7%C there is a V shaped line which joins the A1 horizontal line. On the right hand side of the V section is what we are usually talking about when we mention Acm in conjunction with crucible steel. This is the A Cementite line and it represents the place where all cementite (iron carbide) dissolves completely in the steel. Slightly above this line, I can't remember exactly how far, it is something like 30 to 50 °C above the Acm line you will find on some diagrams a line called Agr. This is the A Graphite line where all graphite dissolves in the steel and it mirrors the Acm line exactly. Now of course if there are other alloying ingredients in the steel these lines will change just a bit, but it is a pretty good guide. Also once a piece of steel raises above this level the carbon doesn't immediately dissolve, if the steel lump is large it can take a few minutes to have it all fully dissolve. There is more to these lines and what they signify in the phase diagram, but I will leave that to others at another time to describe. I suggest that you look up a good PowerPoint or YouTube video on the Iron Carbon Phase Diagram and get edumicated .
  16. I will have to look to see what I have as far as patterns from Al. The method of closing porosity is to raise the steel to above Agr and then after a bit of a soak, you forge it hard. This is fine to do once you have established a bit of a bar and the bar is moving sufficiently. If you have ingots which are too high in carbon or if you have too much sulphur in your ingots it can be an issue though.... If you have an ingot which has porosity and you do a roast at a temperature below Agr, then you will be having troubles with it turning to graphite, so you want to roast above Agr (just a hair above Acm), to avoid graphitization.
  17. To further the discussion on banding agents, or Carbide Forming Elements which aid the process of banding, I just re-read a paper by JD. Verhoeven entitled "Genuine Damascus Steel: a type of banded microstructure in hypereutectoid steels" http://onlinelibrary.wiley.com/doi/10.1002/srin.200200221/full I can't find the full text available free online, but the article is well worth a read if you can find a copy. In this paper John outlines the attempts that were made to determine the mechanism of banding in crucible steel. They took pure 1.5%C steel and added specific Carbide Forming Elements to see which elements contributed to banding and which ones did not. They found that the elements which were most effective in causing the specific type of banding that they were looking for, with very straight sheets of carbides, were Vanadium, Molybdenum and Chromium. Manganese was also found to cause banding, but not as strong as the other elements. They found that the Vanadium and Molybdenum were the most effective at causing strong banding. Phosphorous by itself did not cause banding, although it does have a role in increasing the intensity of the banding. His method of testing was quite good and the results were reliable in the main elements which they tested for. There are other elements which may also cause good strong banding in crucible steel, but these have yet to be determined. Also the elements can either be in the raw ore, or in the charcoal which is used to make the bloomery iron that is used in the production of the crucible steel. This paper had many little gems in it. By reading between the lines it was possible to see the process which Al used to create his patterns back in the early days. He showed how slow solidification of the ingot caused porosity and graphitization of the ingot and how to remove that porosity (with graphite in the porosity) in ingots and render them usable again, among other things. As I said.. well worth a close read.
  18. That is an awesome book and a real good start if you want to understand how steel behaves, and why. JD is a great guy and this is a real gem which he was generous enough to share with bladesmiths. This was made with a few additions into an ASM book called Metallurgy for the Non-metallurgist. Well worth downloading the copy... just don't try to sell it, that caused some smiths some problems in past years.
  19. To be completely honest, we have no idea what role tannins play, it is a readily converted form of carbon which will aid in cleansing the steel of impurities, it can act as the building blocks of carbon nanotubes, but the most important thing is that the ancients thought it was important. Most of the old recipes were rich in tannins. I guess that time will reveal why... The process at Deccani / Hyderabad / Trichinopoly (same location different names) did not add carbon at all. They used two different types of metal which they combined in a crucible. One type was high in carbon and was a type of cast iron, the other type was more of a bloom iron and low in carbon. I am sure the processes at the Deccan changed over time, but I don't have any accounts of an earlier process which used organic matter or charcoal added to the charge. If anyone has copies of the early accounts from this location please send me a PM..
  20. I understand the nervousness, do you have a K- Type thermocouple and a way of plotting the output of a multi-meter? If you do, you should be able to find out the actual carbon content of your ingots by sitting an ingot on a thermocouple (KO wool insulated thermocouple) and then put the thermocouple and ingot on a piece of KO wool to insulate it from the floor of the floor. As you raise it up to 1100 degrees you will get plateauing of the plot line as you cross phase transformation lines. You can use the upper marks to work out what the carbon content is in your ingot... That will tell you if it is worth even trying to forge it.
  21. I had the same thought Daniel, I am not sure why he did it that way, without any flux tapping etc. It seemed a bit strange, but then again I do wootz not bloom iron
  22. Hi Jan, the clay coating was to stop erosion of the side of the crucible by the flux, I use a similar product over here called Furnascote. It helps the crucibles to last longer and it reduces the uptake of carbon into the ingot from the graphite in the crucible. The reason that the banding spacing was not as wide was to do with the roasting time, it needed a longer period of roasting to widen the spacing between the bands of carbides. It meant that the secondary dendrite arms where not fully dissolved, that is what increases the spacing of the cluster sheets. He also mentioned that it needed more thermo-cycling which would increase the strength of the pattern as it causes the carbides to grow in place and if you do it over the right temperature range, the carbides will become spherodized.
  23. I'm not sure about the actual mechanism, but Al did say that the Hydrogen lowered the melt temperature. You don't want nitrogen in the ingot as that will make it brittle... very bad . As far as I can see, having more complete carburisation would not lower the actual temperature where the charge became fully molten, it would just help in the absorption, so it would start melting earlier. The point of full melting of the charge is a factor of the carbon content not how well it is absorbed by the metal as far as I understand. It is something that I do not fully understand and I should do some digging to find out exactly what is going on in the melt. It is my guess that just as nitrogen alloys with the iron in the ingot to make it harder and more brittle (not desired), the hydrogen also can alloy with the iron to make it easier to forge and also any alloy lowers the melting temperature. I am convinced that it is more than just creating a reducing atmosphere. That is a really good question Dan, the reason that most people don't use organic matter is that it is just harder to control the carbon content in the final ingot. Most modern smiths use a variation of the Deccani process which in the latter days didn't use organic matter as far as I remember. You get several benefits from the addition of organic matter rich in tannins, but the precision is what you lose... you get more failed ingots and that is a bit of an issue for most smiths who aren't made of money and time. The Deccani process allows much more precision and consistency in the final ingot quality. That is it in a nutshell, I hope that helps a little.
  24. Firstly you don't want to have an ingot which is 2.2% carbon or even 1.8% carbon, or you will end up with something that a beginner will have a really hard time working with, they are more prone to cracking and hard to work. If you add charcoal to a melt, it is 100% carbon per weight, so you add 15 grams of charcoal in order to get 1.5% carbon in a 1kg ingot. It works the same with graphite. However if you add organic matter to a melt you need to know how much organic matter is actually going to be released by that wood or bark. Wood or bark is 50% carbon by weight, so why do you get only 20% approx. of charcoal from burning wood? The other half of the carbon is released as gas and is burned in the process. So if you add organic matter to a crucible and then seal it, you get the total 50% of the wood raw dry weight being picked up by oxides and by the metal instead of only 20%. That is the basic theory. Adding organic matter is far from a precise way of doing things, and oxygen and oxides will mess with any well laid plan as Jan pointed out The metal won't pick up all the carbon unless the carbon source is finely ground and mixed with finely ground metal, that is why it can be problematic. I find that adding metals with different carbon contents works well for me and it is very precise.. PS. I modified my slightly confusing previous post to make it more clear.
  25. Jan, as you make charcoal, you have different hydrocarbon gasses burned off during the process. Hydrocarbon... hence you are losing your carbon to the air and fire. Wood is about 50% carbon per weight, and if you have a roughly sealed crucible, the gasses will be absorbed in the melt to a large degree. Jan using your calculation of 22% of organic matter being carbon will give you twice as much in the ingot resulting in cast iron, and using a calculation of 50% weight of carbon in organic material will give you good steel, if you seal your crucible.
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