How wootz blades were forged?

[ariel]

It so happened that I bought a wootz Pulwar about a year ago. It came ... broken in half. Insurance paid me back, but I'd rather have the sword:-((((

But there was an interesting feature : the break showed internal structure of the blade.
So, I have decided to show how the wootz ingot was transformed into a blade.
I drew a sequence of images. Just do not criticize me for bad artistry: I never had anything more than C- in my elementary school.
From left to right:
1. Ingot in its final form consists of 2 fractions: the bottom part has good wootz with all the dendrites. The upper part collects the junk, the slug etc.
2. The upper part is deeply notched
3. Then the notched ingot is doubled on itself, with the " dirty" part becoming the inner one.
4. The blade has its edge and sides made out of "clean" wootz, and the "dirty" one is open on the spine.

Next, picture of the broken blade: one can see the junky innards on top of the blade.
Next one,- another sword, with a "crack" on the spine. This is where the junky part of the blade shows. Then the smith fills the crack with a wire. Or not.

[RobT]

Ariel,

In his online monograph (Iron, Steel and Swords [https://www.tf.uni-kiel.de/matwis/amat/iss/index.html]), Dr Helmut Föll (materials scientist) says that crucible damascus steel swords contain no slag because the steel became molten inside the crucible (see https://www.tf.uni-kiel.de › matwis › amat › iss › kap_a › backbone). The high carbon content of the steel was what allowed it to melt inside the furnace. If I understand it correctly, the heavier weight of the steel caused it to collect on the bottom of the crucible and the lighter slag rose to the top. I am just mentioning the above. I don't know enough about the matter to say whether Föll is right or not. From what I have read, wootz investigator Dr. Zaqro Nonikashvili has used a variant of this principle to charge his crucibles. He divides the iron into two equal portions. One portion is put into the crucible and is covered with ground glass. The second portion is mixed with carbonaceous material and is placed above the the ground glass. The glass becomes molten long before the iron becomes hot enough to absorb any carbon from the carbonaceous material. As the iron above the molten glass heats up enough and begins to absorb carbon, the molten glass forms a barrier that prevents the iron in the bottom of the crucible from absorbing any carbon. The carbon rich alloy in the top of the crucible is heavy enough drop down through the glass but the excess carbon is not. The carbon rich alloy then gives up some of its carbon to the iron in the bottom of the crucible. That iron becomes high carbon steel and melts.

Sincerely,
RobT

[ariel]

That is fully consistent with my “ scheme” that shows the final structure of the cooled down ingot: wootz at the bottom, junk on top.

I thought that seeing the internal structure of a wootz blade was kind of fun: not often do we have an opportunity to see cleanly broken wootz blade.

From the practical point of view, the crack at the spine of the blade is important: we often see patinated blades with no visible wootz pattern. But if we can detect a longitudinal crack at the spine, filled with wire or not, we can be sure that the blade is wootz and start polishing and etching it.

And you are correct: Nonikashvili is perhaps the best living wootz- maker.

Thanks for the comment.

[Ian]

Ariel:

As I read your explanation, it requires only that there be two zones of different composition: one being wootz proper, the other being some mix of other components that are inferior in quality. Then they are folded and forged as you describe.

The "other components of inferior quality" seem to be crucial in the manufacture of proper wootz. The account of Dr Nonikashvili's method describes the use of a glass layer. Presumably some of the inferior material that collects at one end of the wootz ingot contains remnants of the glass and therefore should be high in silica content. Have tests been performed on historical wootz ingots to determine what other components such as glass may have been used in its manufacture? It seems to me that if one simply did surface tests of wootz weapons the "other components" may be missed because they were folded to the interior of the piece, and so some examination of the ingots themselves would be necessary.

Also, do you think the presence of these inferior components may have jeopardized the integrity of wootz blades, making them inherently more likely to fail?

Very interesting observations on that broken blade. It did not break in vain ...

Ian

[ariel]

Ian,
You are correct: my diagram does not touch on the composition of wootz, it only shows what the smith did with the already manufactured ingot.
Nonikashvili’s method is unique and I am not smart enough to judge its faithful replication of the ancient process. But all old descriptions mention only iron ore and leaves ( a source of C).

The famous paper by Verhoeven, Pendray and Dauksch “ The key role of impurities in ancient Damascus steel blades” provided the best available analysis of the chemical composition of the older blades studied by Zschokke in 1924 and some newer samples.Interestingly, Si concentration was quite high in all of them, likely contamination with sand (????).

The authors postulate that the iron ore was coming from different sources and that the majority of old wootz blades were actually of rather poor quality to the point that one out of 4 swords donated by Moser for Zschokke study had too low C content to even qualify for being a true wootz.

But again, what I presented is how the old masters dealt with the ingot to maximize the use of real wootz component in the working areas of the blade, not how the ingots were made.

And you are right: the pulwar blade did not brake in vain. Let’s take our collective hats off and give a 21 gun salute to the old warrior.

[kai]

booom

[kai]

Hello Ariel,

My condolences!

Thanks for the pic - could you try to get a macro shot, please? It seems to show 2 rather than a single cold shut from forging; I don’t think I’ve seen that before...

The folded structure of many wootz blades has been discussed here before. I agree with your general assumption that the wootz often got folded upon itself (despite having a tough time to imagine the forging work needed to end up with a neat elongated blade with intact internal configuration).

From what I’ seen of ingots, they seem to be clean steel also at the top. The dendrites seem to be better developed towards the lower part though. The folding may well be intended to expose this structure rather than hiding any impurities.

Since wootz needs to be forged at “low” temperatures, any cold shut after folding the ingot upon itself may well be from working at too low a temperature to achieve proper welding. It’s a thin line...

Regards,
Kai

[ariel]

The break area on my example was not polished and etched.
There is a similar example ( polished and etched) in a Russian book by Kamil Khaidakov: much better resolution of the junky area.
Folding was not intended to hide anything: it just assured that the important parts of the blade used the best part of the ingot.
Quite possible the junky part was squeezed out through the crack in the spine. Just a thought.

[RobT]

Ariel,
According to Föll, all true crucible steel has a high carbon content because the alloy must be at least eutectoid in order to become liquid at the furnace temperatures of the time. If it had no affect on the function of the blade, the SI content is irrelevant. Remember, the people that made this steel and forged these blades had no concept of modern metallurgy. If the SI didn't break it, they weren't about to fix it.
Ian,
In her doctoral desertation (Crucible Steel in Central Asia: Production, Use and Origins), Dr Anna Feuerbach mentions a ring of glassious material inside the crucibles. If I recall correctly, Nonikashvili says that finding was the reason for his experiment. I wonder, however, about the possibility of any glassious material sticking to the steel of the ingot and being incorporated into the blade during forging. Even under low forging temperatures, that material should become liquid and run off the steel right away, no? I think that any SI content in the steel would be in the form of an alloy precipitate as the crucible charge cools. I am more than a bit unclear about this but, it appears from what I have read of Föll's monograph, it is the way in which the precipitates (C, SI, P, etc) are manipulated during forging that governs the strength/durability of the blade.

Sincerely,
RobT

[Ian]

Originally Posted by RobT

... Ian,
In her doctoral desertation (Crucible Steel in Central Asia: Production, Use and Origins), Dr Anna Feuerbach mentions a ring of glassious material inside the crucibles. If I recall correctly, Nonikashvili says that finding was the reason for his experiment. I wonder, however, about the possibility of any glassious material sticking to the steel of the ingot and being incorporated into the blade during forging. Even under low forging temperatures, that material should become liquid and run off the steel right away, no? I think that any SI content in the steel would be in the form of an alloy precipitate as the crucible charge cools. I am more than a bit unclear about this but, it appears from what I have read of Föll's monograph, it is the way in which the precipitates (C, SI, P, etc) are manipulated during forging that governs the strength/durability of the blade.

Sincerely,
RobT

Rob,

Thank you for the feedback. Interesting to know that glass featured in the manufacture of crucible steel. It is a while since I read Ann's thesis and I had forgotten that point.

I'm no expert on the history or properties of glass, although I think the old masters of wootz-making would have had silica glass available. In its finished state this is mainly an amorphous (i.e., non-crystalline) form of silica (SiO2). Thermal decomposition of silica glass can occur at sufficiently high temperatures and I don't know whether that happened during the making of wootz. According to Schwind (2002), depending on it's composition, some glass will melt at temperatures as low as 500 °C (900 °F), others melt at 1650 °C (3180 °F). As far as glass particles getting incorporated into the wootz, that seems at least a possibility, especially if these are sub-micron in size.

When discussing the Si content of wootz, I think Ariel was likely talking about an elemental analysis for silicon (Si). We don't know if the form of silicon present is elemental silicon, amorphous silica, one or more silicates, or some other chemical form.


Ian

[Bob A]

I thought this information on production of silicon carbide was of interest.

The simplest process to manufacture silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F). Fine SiO2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material.*

Sand would obviously melt into a glass at the temperatures involved in the wootz process.

In light of above posts, I may be merely belaboring the obvious here. Nonetheless, the reference to plant material in the Wikipedia entry discussing silicon carbide was interesting.


*https://en.wikipedia.org/wiki/Silicon_carbide

[Richard Furrer]

Ariel, No need to notch the ingot...it folds at the top on its own during forging...for two reasons. One being that unless high forces are delivered it is the natural tendency for metals to move more at the surface that the middle and they "fish mouth" or "duck bill". After more light forging the edges of the steel touch and you get a folded appearance. The second is that the poorest part of the ingot is the top and it almost always had gas pockets from the cooling process and as such is less dense and moves differently under the hammer. Often collapsing onto its center as forging progresses.

I have yet to see a "sound surface" at the top of an ingot. All ingots have some surface irregularities in them in the form of pockets or bulges and if the porosity is not visible it exists in micro form with the most porous at the top.

Often the top of the ingot becomes the spine of the blade. I would call the folded over bit a seam and I have seen several where the seam wanders from the spine onto the flat of the blade. In one case it fell off and was cold riveted back into place.

Ariel...if that broken blade is for sale I would like to purchase it and do chemical, hardness and microscopic analysis on it to add to my database.
That goes for anyone else who has broken crucible steel blades or bits and pieces.


Edit: It is a simple matter to add silicon to the steel when it is liquid (very hard to stop if glass is present actually) and I have yet to see any glass survive in the bar once forged out to a blade. It all goes away when the ingot is being forged into bars. This is due to its liquid nature at temperatures used for forging and also that if allowed to cool on the anvil it is untempered glass which is very brittle and simply falls away when left to its own devices after a day of forging.

Edit Edit: I would guess that large grain size (and shipping abuse) was the cause of the fracture. If the break is at all black on the edges then it could also have been a flaw from the quench which waited for the stress of shipping to finally break. Cracks caused in forging or the quench or almost always black color due to high temperature oxidation. In modern blades if the crack is yellow or blue then the crack was in the tempering stage of manufacture...the color is again due to oxides, but lower temperature oxidation.

Ric

[ariel]

Richard,
What sale are you talking about? :-)
Send me your address and you will get it for free. I shall only be delighted to contribute something useful to the community of wootz-smiths.
One condition: after you polish and etch the break, could you send me a pic of it, please?
And if something interesting comes up from the measurement you will be taking, please let me know. OK?

Ariel

[Ian]

Ric and Ariel:

Please post the results here also.

Ian

[Richard Furrer]

Absolutely Ariel, The Professors I work with have just added some new analytical tools and we can do better testing now than in the past.
I will tell you what we discover.

Let me know everything you can about the sword so we can include that in the data as well.

Ric

[Bryce]

Thanks for posting your cloudy/silver lining breakage and your great explanation Ariel. Is their a wootz pattern visible on the face of the blade? Can you post a photo?
Cheers,
Bryce

[ariel]

I can see islets of wootz pattern, and tried to photograph them with my iPad, but the camera was not able to catch the image: there is quite a lot of small pitting.
It has to be polished and then etched professionally (I am an amateur). I am sure Ric will be able to do it zillion times better when he gets it.

Of course, after he sends me his mailing address:-)

[ariel]

Ric,
I know only it used to be a pulwar that I won on e-bay from GB. The blade had no “Indian ricasso”. Persian? No inscriptions, no decorations, no names or dates.
It ain’t no donation from Moser.

Yes, I know it is frustrating, but that’s life.



Need your address, man!

[Richard Furrer]

Ariel,
I sent a private message, but it is 3179 May Road Sturgeon Bay, WI 54235
Ric

[ariel]

Ric,
It's on the way.

[Richard Furrer]

Ariel, It arrived in one piece.
Ric

[ariel]

No more broken surfaces to polish and etch? What a pity...:-)

[Bob A]

In a discussion on another forum regarding Damascus steel, someone posted a youtube video in which Alfred Pendray was able to produce wootz steel. While the samples produced at that time were not to his satisfaction, I found the video quite interesting.

It may also be of interest to others on this site. A search revealed that Pendray's work is not unknown in these parts. However, a search for this video was not productive, so I leave this link:

https://www.youtube.com/watch?v=OP8PCkcBZU4&feature=youtu.be

Directly clicking on the link did not work for me, but to cut & paste in a browser seemed to bear fruit.