Why were the ingots mostly round?

[Jens Nordlunde]

I have seen in several places, that the wootz ingots are very hard to get oblong so it could be used for a blade. By far the greatest part of the ingots were used for blades, and some of the ingots were not round like we mostly know them, they could have very different forms. When most of the ingots were used for blades, why were they not ‘pre formed’ for this purpose? It must have been possible as some of them were ‘loaf’ shaped, which in a way was a ‘pre forming’.

[Gt Obach]

Hi Jens

in my opinion..... one of the variables to developing a good watered pattern is working the steel .... the more heat cycles and the more forging should help to produce a nicer pattern..... ...

i'm sure they tried to melt wootz in bar shaped crucibles...... but the pattern would be very dendritic and not very many forge cycles would be needed to produce a sword.......

--- since they made their own crucibles ...i would think they could shape them in the form that would be best for swords...

Greg

[Jim McDougall]

Hi Jens,
Metallurgy is probably one of the most difficult aspects of studying these weapons for me, as it is obviously so technical, but your observation is well placed and seems like a logical question. In rereading some of the fantastic work of Ann Feuerbach she notes certain differences in the shapes of the crucibles, i.e.conical (eggplant) shaped in southern India, and elongated, pear shaped or light bulb shaped in Sri Lanka, while Hyderabad crucibles were cylindrical, similar but shorter than those in Central Asia.

As a layman, it is my impression that the shapes of the crucibles must have had something to do with the manner of stacking them in the furnace, as well as has been mentioned, some consideration for heat transfer . It seems that since the cakes of metal needed to be reheated to be forged the molten or redhot metal could be drawn into the necessary elonged shape fairly easily.

This sounds like a question that Ann or some of the metallurgists here might have an answer for. Now you have me curious too!!

All the best,
Jim

[Justin]

I keep hearing talk of wootz being melted and cast ,this has puzzeled me since to the best of my knowledge this would homogenize the metal and detroy the different layers of steel.So how does it work?

[B.I]

its a good question, and one i look forward to 'spectating'.
jim, i think that we need both here. anns historically academic anaysis would be great, but also greg is as hands-on talented as they come, and i would like to hear more from him. i think if we tickle his curiosity enough to get him to expand his opinion, we will be pleasantly surprised at the results :-)

[Jeff Pringle]

I'm thinking that it's easier to get a crucible to maintain it's structural integrity at high heat if it is round, and not too tall.
Also, the difficulty in forging out the metal is a problem with all ingots, the first stages are the difficult ones and would exist with either round or long ones, so the benefit is not as great as it would seem.
Round, compact ingots also might be less prone to casting flaws, bubbles and/or slag inclusions, due to the surface area to mass ratio - it really sucks when you spend a bunch of hours forging something out and then find a flaw.
What do you think?

[PUFF]

I had tried a couple wootz smelting with no success. And what I can tell you is that button shape crucible 's much more easy to work with.

First of all, oxygen protection is a must for wootz smelting. In wootz furnace, the crucibles are required to be arranged at the combustion zone (highest heat, ~1400 C). Since atmospheric condition 's not totally reduction, molten steel surface need to be protected and minimized.

The second reason is for the crucible 's stability, as Jeff mentioned. Even modern refractory get soften a bit at that temperature. Wootz crucibles are need to be heated at 1200-1300 C for several hours. Good design 's required or crucibles will be fail (very messy, 'liv me).

Third reason 's also ceramic thing. The fact that the higher refractory materials has lower plasticity and green strength 's another major constrain for their shape. You cannot make a very complex shape. And cup-shape crucible 's difficult enough for hand-forming pieces.

The forth reason; dendritic steel 's VERY difficult to forge down, especially when heat 's required to be under 800 C. Even with annealed button, smiths may require 30-40 reds (heat cycles) to forge button flat. That 'coz of dendritic structure 's required to be broken into small. And after the button has been "forge soften", only another 10-20 reds to go to bar or other shape. If the metal was made as bar, 50+ heat cycles still need for shaping.

The metal cannot be cast to shape 'coz the "as cast" material 's too brittle for any application.

[Jens Nordlunde]

Hi all, sorry for my absence.

Thank you for the answers witch I find very interesting. As the one who knows little about the subject, I have an additional question.

From the answers you have written I understand, that the bigger the ingots were the more difficult it was to make them. As far as I know the ingots varied in size from a few hundred grams to about 3 kg, but most were made for making two sword blades out of an ingot. If the big ingots were so difficult to make, why did they not make the small ones only? Is it possible to forge left over from two different ingots together and get a good result? How close it the wooz pattern in the ingots made in the same furnace?

[Jeff Pringle]

If the big ingots were so difficult to make, why did they not make the small ones only?

Taken as an entire process, I don't think there is a huge difference in difficulty between big and small ingots, and there are considerations such as efficiency of the furnace, and success rate of the final product.
Plus, as anyone who is making the stuff can tell you, many of the 'two-sword' ingots get to be 'one sword'- or 'several knife'-sized by the end of the forging process - if you only made ingots big enough for a sword, you'd end up with a lot of knives, and maybe not enough swords!

Is it possible to forge left over from two different ingots together and get a good result?

They did it back in the day, I don't know if anyone has gotten the technique down in modern times.

How close it the wooz pattern in the ingots made in the same furnace?

Very different, even within the same batch or ingot. I think Ric Furrer did a test of a Sri Lankan(?) type of crucible that was designed to be laid on it's side when the metal was molten, to give an oblong bar - IIRC, two ingots made of the same metal fired at the same time gave very different patterns in the final surface.
I find a fair degree of uniformity in patterns within an ingot, but each ingot varies in pattern depending mainly on carbon content and solidification rate.

Justin - this article explains the patterning in wootz steel -
http://www.tms.org/pubs/journals/JOM...even-9809.html

[Jens Nordlunde]

Hi Jeff, thank you for your interesting answer.
Since you write that a ‘two sword’ ingot easily could end up as a few daggers ingot, there must be a big difference of how much slag there it in the different ingots?

[Jeff Pringle]

No, not slag - sometimes there are 'air' bubbles that need to be worked around, sometimes cracks appear. Typically slag inclusions in wootz are fairly minor.

[Jens Nordlunde]

I am rather puzzled. ‘Air’ bubbles, what is that, and how do you work your way around them? It is the first time I have ever heard about it.
The cracks are something interesting. I know of course that they appeared; most of the collectors know this, but why? One would think that when a blade is heated and worked on cracks would disappear, that the forging would make the blade more homogeneous, so why are the cracks still there?

[Justin]

Thanks,Jeff.

[PUFF]

Unlike solid state smelting, the wootz smelting turn whole thing to liquid mixture. With slow cooling, liq. slag and liq. metal separated into two distintive phases like water and oil. Most of impurities partitioned into slag phase and floated up to the surface. I don't know about air bubble. Any bubble in the ingot indicates that smelting temperature 's too low and such a low smelting temp could trap some slag either.

Cracks are not "as baked" flaw. They happened when forging stress goes beyond the material elasticity (either forging temp 's too low or hammering 's too hard). Dear Jens, forging would make the blade more homogeneous as slag inclusions were forged out. But flaws like crack (or bubble) could not be closed unless you reach forge welding temperature (~1400 C). Unfortunately, wootz pattern melt down at 900-1000 C and forge welding of cracks or two ingots 's unlikely (possible but very difficult to bring the pattern black ).

Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece. IMO,As a smith, the worst flaw 's quench crack

[Jens Nordlunde]

Hi Puff, thank you for the explanation, I had an idea that it may be like you described, but I was not sure. Also I knew about the heat, but it is better to hear it one more time. Also there may still be some of the forumites who have not heard about this before.
So I suppose that the temperature of 900-100C is the cherry colour Hendley writes about.
Nice to have people like Greg, Jeff and you onboard, when it comes to the construction of our collectives.

[PUFF]

Originally Posted by Jens Nordlunde

Hi Puff, thank you for the explanation, I had an idea that it may be like you described, but I was not sure. Also I knew about the heat, but it is better to hear it one more time. Also there may still be some of the forumites who have not heard about this before.
So I suppose that the temperature of 900-100C is the cherry colour Hendley writes about.
Nice to have people like Greg, Jeff and you onboard, when it comes to the construction of our collectives.

Just a minor correction, 900-1000 C going to be a yellowish cherry, a bit sour for my taste. Nice sweet & sour cherry red 's around 800 C.

[Jeff Pringle]

To add a bit to what Puff said, regarding bubbles:
I said 'air', but really it's carbon monoxide or oxygen, and they occur for a variety of reasons - undercooked ingots mostly (the melt has not reached equilibrium), but since liquid steel can hold more gasses in solution than solid steel, you can find porosity occuring during solidification too.
Regarding cracking, it can occur from working at too high or too low a temperature, or pushing the material too fast - the as-solidified grain stucture needs to be coaxed into a finer, more forgeable state. Impurities in the steel (oxygen, sulfur, phosphorus etc.) will precipitate out at grain boundaries during solidification, and can cause cracking too.
Forging temps for wootz are not high enough for cracks to get welded back together, so they don't go away. As Puff said, "Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece", and that's how those one-sword ingots get to be multiple-knife ingots.
I have some ingot slices that demonstrate most of the flaws you can run across, here's one ingot with some probable CO bubbles - cube is 1 cm for scale:

This ingot also suffered from too much intergranular oxygen and proved to be unworkable, after a lot of work!

[galvano]

Here two ingots.
One with bubbles.
One with cracks. galvano.

[Rivkin]

I don't really know metallurgy, so a stupid question: what if one "on purpose" adds some localized impurity - can it be a seed for the pattern to grow, i.e. the pattern will nicely grow from this point?

Like, for example in the sample above it seems that the pattern "grows" from the sample's surface and is much sparser in the sample's middle; it also nearly absent on the sample's bottom. Could one add something to the sample so it will be an artificial centre of the pattern's growth.

[Jeff Pringle]

I think the pattern difference above is a lighting artifact, with different lighting the pattern should look uniform across the surface.
Patterns in wootz come from the fact that when the steel starts to solidify, the first crystals 'want' to be pure iron/carbon - the impurities in the melt become concentrated in the areas of secondary crystalization, in between the networks of already solid metal. So the impurites do get localized to a degree.
Theoretically, you can control the grain orientation, and hence ultimate pattern, by manipulating the shape of the solidifying metal (by casting into a mold of varying thickness), but I don't think anyone is working on this yet.

[galvano]

it is not a artéfact.
Surface was attacked with ferric chloride.
galvano

[Rivkin]

Originally Posted by Jeff Pringle

I think the pattern difference above is a lighting artifact, with different lighting the pattern should look uniform across the surface.
Patterns in wootz come from the fact that when the steel starts to solidify, the first crystals 'want' to be pure iron/carbon - the impurities in the melt become concentrated in the areas of secondary crystalization, in between the networks of already solid metal. So the impurites do get localized to a degree.
Theoretically, you can control the grain orientation, and hence ultimate pattern, by manipulating the shape of the solidifying metal (by casting into a mold of varying thickness), but I don't think anyone is working on this yet.

Pattern's orientation is going to depend on the sample's size/shape if it is comparable to the grain's thickness, however imho since the interaction between particles here is a short range, the thickness of grains mostly going to depend on chemical composition of the sample.
What I was thinking is that if one locally introduces an impurity, preferrably such that an energy bonding to the pattern if favorable over bonding to the matrix, one can probably create really nice patterns, not very practical, but very nice indeed.

[Jens Nordlunde]

Jeff/Galvano, thank you for showing the ingots, I think they illustrate what you are describing.

Not all the iron ores could be used for ingots, and the Indians knew it. Some ores could only be used for tools while others could be used for weapons and ingots, maybe that is why some of the Arabian merchants had their own people stationed in India to check the ingots before they were exported. If I have understood you correctly, they could however not check if the ingots had ‘bubbles’ inside, and maybe not all cracks could be seen – or could they?

[Jeff Pringle]

If an ingot has a bad bubble problem, it usually is visible on the outside. Occasional small bubbles are easy to work around, so even if they can't be seen they are not a problem. Cracks that mean an ingot is no good usually show up right away, and in descriptions of historical ingot testing that I've read, that's the first thing they checked - how they responded to the first few hammer blows.
The ingot pictured above started cracking (in an ominous fashion) right away, but I kept at it to see if I could coax some useable metal out of it - no such luck!

[Jens Nordlunde]

Jeff, it is interesting what you write about the ingots. I have never, although it may sound strange, had an ingot in my hand. When I started to collect many years ago, there were not many for sale – but that has improved a lot in the last years, like discussed on another thread. I should have remembered the sound test, which can be used on metal, glass, porcelain and probably on many other things.

You write, “Occasional small bubbles are easy to work around, so even if they can't be seen they are not a problem.” Does this, ‘work around’ mean, that you cut the bubbles out when you have flattened the ingot? Or how do you ‘work around the problem’?

[Jeff Pringle]

The first way to work around bubbles is like an insurance policy - Usually the ingots have some porosity on one side, and you keep track of this side as you go from round to square, then make that side the back of the blade. This way they are far from the cutting edge and supported by more metal around them. I've seen old swords at auction with small seams on or near the back that are certainly the residue of ingot bubbles.
The other thing to do is to watch for the subsurface porosity to show up during the round-to-square forging and file/grind them out as needed. Any dips in the surface at this point in the process will be long gone by the time you get to the shape of a blade blank.

[Rick]

While we're discussing wootz ; I would like to dredge up a subject from the forum's past .
Once there was shown a sword with one side showing an active wootz pattern ; oddly enough though on the obverse the steel showed no pattern at all .
Any ideas on how this could have happened Jeff , or any other of our smiths ?

[B.I]

hi rick,
i have a historical opinion on this, as apposed to a metallurgical one.
for some reason, the wootz ingots were small, maybe too small to make a large blade. and so, a blade was made from different ingots joined together. this is why some indian blades have a 'scarf/lap' weld along the blades. also, why there is normally a join along the spine of all wootz blades, where ingots have been sandwiched together.
i am away from my notes, but i believe travernier mentioned this, when travelling with the moghuls in the 17thC. he said that each ingot was always cut in half, to determine the quality of the pattern. a good size sword was made from 3-4 of these halves.
occasionally, you will find a scarf weld, with one side being wootz and he other steel. even rarer, you will find one complete side being wootz, whilst the other is steel or even pattern welding. rarest of all, is both sides wootz, but sandwiched between a layer of steel (presuming it is steel as the colour seemed different). the last is a thick blade, of substantial quality.
the joining/sandwiching/scarfwelding is my theory, not traverniers. he just mentioned about the halves. during my collecting/studying i've heard many different theories about scarf welding, some pretty ridiculous (from stregthening to religious). this is one that i feel happy with, and think that travernier adds some fuel to it.

[Jens Nordlunde]

I see what you mean Jeff. How deep is a crack? If it is not too deep, you could make the blade a bit broader and grind the crack away – or is this solution too easy?

Interesting subject you bring forward Brian. I know tulwars exists having two different wootz patterns, one on each side, or wootz one side and steel without pattern on the other, but if it was possible to sandwich two half’s of a blade together, why does the cracks give so big problems? The wootz should be worked, like Puff writes, at cherry colour at about 800 C, and I understand it is rather difficult to work the wootz at such a low temperature. A higher temperature would make it easier, and also possible to remove the crack, but then the wootz pattern would have gone. I have a feeling that I am missing something – but what?

The attached picture is from a tulwar, I know it is not wootz, but have a look at the picture to the right – what is this, is it a crack or is it a scarf weld?

[Jeff Pringle]

what is this, is it a crack or is it a scarf weld?

That looks like a weld flaw - when doing layered damascus, it's easy to get small areas (or large areas ) that don't join up, that's what they look like in the finished product. If it was a crack, the 'texture' would be different, if a scarf weld, it would be going across the layers at an angle.

A higher temperature would make it easier, and also possible to remove the crack, but then the wootz pattern would have gone. I have a feeling that I am missing something – but what?

The missing bit of info might be that attempting to work wootz at welding temp results in more cracks, turning the ingot into something that reminds smiths of cottage cheese. It's not that the pattern goes away, the whole buiscut crumbles.
Which is interesting, because there are obvious examples of two ingots welded & turned into a sword and scarf welds joining two halves of a wootz blade as B.I. points out - this has mystified western smiths for hundreds of years. Obviously, they had a different way of welding than modern smiths are used to.
So the ways of getting non-patterned areas on wootz are -
- weld wootz to non-patterned steel, this should show a seam down the back/near the edge
- some methods of working wootz give it a decarburized outer layer which needs to be sanded off before the metal will show it's pattern - this usually shows up in patches, though - you'd have to be a very forgetful smith to leave an entire side of a blade in this condition
- obviously, sanding can remove the pattern, but re-etching should bring it back - that'd be the first thing I'd look at if a blade had one sided wootz and no visible seam on the back.
Here is a small test I did - wootz sides welded to 1070 commercial steel - the lower line is the weld zone, the upper line is the transition between hardended and unhardened metal - note the wootz pattern dissappeared in the hardened area. this method of pattern removal would be impossible to do on the side-to-side of a blade, but could happen on a top-to-bottom direction.