Wootz, an ancient solution to a steely problem

This is the story of the real life equivalent of Valyrian steel.

In the books, valyrian steel is described thusly:

"Lighter yet stronger, and nothing holds an edge like it. If you take a whetstone to a Valyrian blade, you will need another whetstone, or maybe another hand to hold it."

"Nobody knows how the Valyrians forged their steel. Less than a handful of smiths can now even reshape it. The process, like so much of their civilisation, was lost in the Doom. Many claim they wove magic spells into the molten metal and blasted it with dragonfire. When you see a Valyrian blade, smokey and dark as if drinking in the sun and rippling with a thousand foes, you may not scoff so loudly."

In real life, Valyrian steel was inspired by Wootz, or "damascus" steel. Wootz hails from Indian sites in Konasamudram, Nizamabad district and Andhra Pradesh (Lowe 1990; Voysey 1832) and Gatihosahalli in the Chitradurga district of Kamataka (Freestone and Tite 1986; Rao 1970).

It is a heterogenous steel, with a soft base and hard carbides.

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I did an audio transcript of this incase you're not into reading. Check the youtube link.

This is a ceramic crucible, heated until the steel is molten in a brick furnace, with forced air being pushed into the charcoal fires to feed the flames. In the crucible is iron ore, charcoal, and glass (which melts and floats on top of the forming steel, protecting it from air).

The wootz process involved very slow heating, followed by slow cooling, occurring over 24-48 hours. This lead to distinct patterns of low carbon steel with a lattice of high carbon steel that provides good edge retention in a shock absorbing core material.

Pieces of bloomery iron were heated for days in sealed crucibles with a carbon-containing material until enough carbon had been absorbed for the steel to be formed as a liquid, at 1300 °C–1400 °C. The carbon content of the resultant button of steel was about 1.5%.

This technique disappeared around the 1750's, likely due to the depletion of the mines inregion which removed the incentive for making this style of steel, as the specific alloying compounds in the ore from a small group of mines allowed this steel to form surface carbides. The end of the age of wootz lead to the use of more conventionally produced "bloomery iron", an earlier steel, until modern monosteel was made in the late 19th and early 20th centuries via the bessemer process.

Wootz must be worked colder than modern monosteels, or even lower carbon ancient steels. When worked too hot, the carbides (cementite aka ferric carbide or Fe3C) would dissolve back into the steel, resulting in a homogeneous, ultra high carbon steel was was brittle an unsuited to use.

Here is a small button of wootz. You can see the distinct banding around the periphery of this disk of steel, caused by the carbides randomly segregating intro high and low carbon regions, which crystallise during the slow cooling process.

The very high-carbon crucible steel (wootz) which was allowed to cool extremely slowly after liquefaction, so that the cementite (iron carbide, Fe3C) crystals were large enough to form a visible pattern on the surface.

wootz cakes have been known to display a distinct white colour due to the presence of white streaks of cementite formed during solidification. This typical white color was noted by Greek historians by specifically stating that the wootz steel received by Alexander from India in 326BC as “white iron”. (R. Balasubramaniam, 2007)

Here you can see the white lines of course cementite. The dark background is tempered maternsite, or sorbite. It is a shock absorbing crystalline arrangement of iron and carbon. The cementite crystalline structure of the white lines is hard, and keeps the edge from dulling.

And a cross section reveals this even better. This particular button has a lot of white lines (cementite) which would mean it is quite hard and perhaps brittle.

Here's an image demonstrating the variety of results you can achieve using different steel sources, like carbon steels, wrought iron, high alloy carbon steels, and mixes of the aforementioned.

The iron ore used in india at the time contained vanadium which assists in carbide segregation, giving wootz its unique properties. (J.D. Verhoeven, A.H. Pendray, W.E. Dauksch, 1998)

Once the steel is slowly drawn into a sword, it is heated till it glows cherry red. It is then quenched, or rapidly cooled.

Individual makers had various methods for quenching, some opting to use forced air (which cools more slowly than liquid quenching, reducing the chance of stress fractures, but also reducing the hardness of the cementite and thus reducing the edge retention)

Others chose to quench in oil, brine, or hot water. Some even used acidic solutions, which cool even more quickly than water. This risks cracking the blade, but achieves the very hardest carbides in the cementite bands.

The fast quenched (water and acid) blades required tempering, which is a stress relieving process in which you heat the blade to a few hundred degrees (200c), which relaxes the soft sorbite regions whilst leaving the martensitic derivative cementite intact.

Here's an etched portion of a bar of wootz, showing the random swirls of dark sorbite and lighter cementite. This shows a fairly tight grained swirly appearance, known as Black Wootz, or Kara Khorassan. it is among the rarest forms of wootz, along with Kara Taban, and "ladder wootz", which is made by selectively grinding and then reforging bars of wootz to form artistic patterns.

Here we see Kara Khorassan on the left, and Kara Taban on the right. Note that Kara Khorassan is darker and tighter in terms of the swirling crystalline structures. It is also more desirable the Kara Taban

This is ladder wootz, It is made via various forging process involving grinding the bar of steel and the reheating hand hammering the bar flat. This leaves lines or rings in the steel, caused by compressing the grain during the reforging. It is purely decorative, and only found in the highest grade wootz swords.

Wootz was widely exported, and via the Volga trade route reached norther Europe and Scandinavia.

This sword features a famous signature, saying ulfberht. We don't quite know what the significance of the word is, apart from the direct translation being "bright wolf", but the highest quality swords of the age had it. It is assumed that it was the identification of a smith, or blacksmithing house. It was presumably made by the Frankish, as the lettering indicates it is not Scandinavian, however many are found in norse burials, as it was high prized by vikings.

These swords were thought to have used imported wootz steel, taken by the vikings from oriental regions of the world via the Volga trade route. It is my opinion that they traded not just furs, but walrus ivory for this steel. It is also possible a European smith worked out how to make high grade carbon steel, and kept it a well guarded secret, although trade is more likely. Some sources say the swords were manufactured by monks, although this has not been proven via primary sources.

So famous were these swords, that imitations were made at the time, often bearing misspelled inscriptions and inferior steel - we're only just finding out how many are real today, via x-ray diffraction, which reveals the crystalline structure of these swords.

This viking era spatha (reproduction by Patrick Barta of Templ Smithy) has a more typical construction than the previously mentioned ulfberht swords.

This is made by twisting bars of soft iron and harder steel. The hard steel forms the edges, and softer iron the hard, swirly core. The pattern is repeating and consistent, differentiating it from wootz. It also has no carbide segregations, relying on the electrochemical differences in steel types to show dark and light areas,

Diagram of multi - bar pattern welded process. To reinstate my point, this is NOT wootz, simply another method of achieving hard edges and a soft core.

True wootz does not have hard edges and a soft core, but rather hard carbides all throughout the soft steel body. It is a hybrid between pattern welding and monosteel constructions.

This is one of my wootz swords.

It's a shamshir (sabre) from 1600, made in Isfahan, in modern day Iran.

I can't do a writeup on this subject better than those that already exist: http://auctionsimperial.com/om-the-persian-shamshir-and-the-signature-of-assad-allah/?locale=en

The inlaid signature is worse for wear, but looks like the shortform of Assad Allah Al Asfahani, a prolific bladesmith between roughly 1580-1630.

The wootz is Kara Khorassan wootz (black wootz - has a distinct styling, being dark with fine light swirls). Other variants like kara taban and ladder wootz also exist, haven't got one yet.

Blade has gone through resharpening during its lifetime, probably quite some time ago.

Here's a closeup of the wootz on my shamshir. Note the tight swirls of the Kara Khorassan wootz.

Here's another of my wootz swords, this time a turkish Kilij circa 1780. It has a pronounced "T" shaped spine which gives it extreme stiffness, but a very fine, sharp edge. These were used in slashing draw cuts, and were very good at dealing with softer targets (padded armors, flesh, horses etc).

Sources:

(Sources are of mixed formats, sorry for my laziness)

R. Balasubramaniam, (2007) "Wootz steel received by Alexander" Indian J Hist Sci, 42, p. 511

J.D. Verhoeven, A.H. Pendray, and W.E. Dauksch, (1998) "The Key Role of Impurities in Ancient Damascus Steel Blades", JOM, vol. 50 (iss. 9) , pp. 58-64.

Lowe, T. L. (1990). "Refractories in high-carbon iron processing: a preliminary study of the Deccani wootz-making crucibles.". Ceramics and Civilization. Cross-Craft and Cross-Cultural Interaction

Voysey, H. W. (1832). Description of the manufacture of steel in Southern India. Journal of Asiatic Society of Bengal, 1: 245-7.

Freestone, I. C. and Tite, M. S. (1986). "Refractories in the ancient and preindustrial world.". Ceramics and Civilisation. Pittsburgh: American Ceramic Society, 35-63.

K. N. P Rao, J. K. Mukherjee, and A. K. Lahiri, (1970) "Some observations on the structure of ancient steel from south India and its mode of production", Bulletin of Historical Metallurgy, 4, pp. 12-4.

http://auctionsimperial.com/om-the-pe

Further reading:

B. Bronson, (1986) "The Making and Selling of Wootz," Archeomaterials, 1, pp. 13-51.

J.D. Verhoeven et al., "Microsegregation and Banding in Hypereutectoid Steel: Damascus Steel," ISS Trans., 25 (in press).

R.A. Grange, (1971) "Effect of Microstructural Banding in Steel," Met. Mat. Trans. A, 2 , pp. 417-426.

Not a journal article, but referenced:

https://historytelling.wordpress.com/