I get the question “What is wootz” quite often, and like so many questions in life there are both simple and complicated answers. This question touches on metallurgy, semantics, and history, so it is no surprise that things could get complicated very quickly. It is easy to get caught in a quagmire of debate about the definition and that doesn’t help anyone. Because it is a very complicated topic I will be breaking it up into multiple “episodes” to make it more digestible.
My “expertise”, if we were to go so far as to call it that, is really in the making and forging of crucible steels, with a particular focus on wootz…more on the distinction between these two later. I have been making my own crucible steel and forging it into blades since 2001, and I have produced many hundreds of ingots, which equates to literal tons of material. I have forged out hundreds (thousands?) of blades along with selling bar stock to other bladesmiths. While I have a reasonable knowledge of the history of the material, my strength is in the making of new steel and blades.
First, here is a basic, technical explanation of wootz to get things started. I am going to present this as bullet points to separate out the several criteria and provide a little context for each.
-UHC (ultra high carbon) steel, typically falling into the 1.2%-1.8% carbon range. For comparison the majority of modern steels are 1% carbon or below. This very high C% is responsible for many of the aesthetic and performance characteristics of wootz.
-Achieves a fully molten state. This differentiates crucible steels from most other historical processes, in which the iron/steel never became fully molten, thus trapping pockets of slag within the iron/steel. The absence of trapped slag particles in crucible steels creates a very different material than the “bloomery” steels that were made through other processes.
-Solidifies within the melting vessel to become an ingot. This differentiates from many modern steels, which do achieve a fully molten state but are then poured into moulds or are otherwise cast into a different shape for solidification.
-Relatively small ingot size. Historically the ingots were typically 2kg or less, but I generally define this as 4kg or less. The basic criteria is that the material is made in small units that are suitable for an individual smith or small team of smiths to forge out by hand. This criteria is partly to remain in keeping with the historical methods and partly because larger ingots actually develop quite different characteristics.
-Low alloy levels. In the historical “wootz” we generally see total alloying (excluding carbon) of less than 1% by weight. This is worth noting since even the simple 10xx steels typically reach or exceed this level just in the manganese and silicon contents. The proportion of elements present in historical steels also tends to be quite different than in modern steels.
-Shows a visible pattern of carbide concentration. It is not clear to me whether this was an absolute criteria in the historical period, but among modern collectors the visible carbide pattern is extremely important. Specifically this is a cementite (carbide) driven pattern; some lower C steels show banding of pearlite rather than cementite and this is a quite different effect.
I want to finish this initial article by noting that “wootz” is a more specific sub-category of “crucible steels”. Crucible steels meet many, but not all, of the criteria laid out above, and just like wootz there are both historical and modern examples. I want to be clear that I don’t view one as being inherently better than the other, but instead I find it easier to communicate with customers, collectors, and other smiths when there are clear, shared definitions to work from. “Crucible Steels” should meet all the criteria above EXCEPT those related to the chemical makeup; the levels of carbon and other alloys might be quite different than those found in wootz. Also, crucible steels may or may not show a visible pattern of carbide banding. As noted above, “wootz” is a more specific sub-category of crucible steels, but this should not necessarily indicate that one or the other is superior.
If you have any questions or comments please email them to me directly. I have a very busy schedule so I can’t devote time to dealing with Spam comments and Trolls on my blog posts. I do want to hear feedback from actual readers, but I don’t have time or patience for Bots. -Peter