How wootz blades were forged?

ariel · 19th September 2019, 04:33 AM

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 · 20th September 2019, 04:36 AM

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 · 20th September 2019, 05:18 AM

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 · 20th September 2019, 10:53 AM

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 · 20th September 2019, 12:23 PM

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 · 20th September 2019, 08:00 PM

booom

kai · 20th September 2019, 08:47 PM

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 · 21st September 2019, 01:16 AM

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 · 21st September 2019, 04:28 AM

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

19th September 2019, 04:33 AM	#1
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	How wootz blades were forged? 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. Attached Images

20th September 2019, 04:36 AM	#2
RobT Member Join Date: Mar 2005 Posts: 489	Dr Helmut Föll Disagrees 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

20th September 2019, 08:00 PM	#6
kai Member Join Date: Apr 2005 Posts: 3,254	1/21 booom

21st September 2019, 04:28 AM	#9
RobT Member Join Date: Mar 2005 Posts: 489	Glass in the Crucible 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

20th September 2019, 05:18 AM	#3
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	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.

20th September 2019, 10:53 AM	#4
Ian Vikingsword Staff Join Date: Dec 2004 Location: The Aussie Bush Posts: 4,200	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

20th September 2019, 12:23 PM	#5
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	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.

20th September 2019, 08:47 PM	#7
kai Member Join Date: Apr 2005 Posts: 3,254	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

21st September 2019, 01:16 AM	#8
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	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.