Real wrought iron differs from steel in that it has a texture. Often called the bark, it is easily seen when split. It can also be seen in the surface of a blade when properly finished. When simply polished with a buffing wheel, it tends not to show much of a pattern. When hand sanded, the bark shows to a degree. When hand sanded and lightly etched the bark / pattern really shows. However, it is far too soft to provide a good edge, So we use a proper steel for the edge and put the wrought iron on the outside / jacket of the blade. The process is nothing new.
“San Mai (Japanese: 三枚, Hepburn: sanmai), in the context of metal blade construction/metalwork, refers to a knife, blade or sword that has the hard steel hagane forming the blade’s edge, and the iron/stainless forming a jacket on both sides. It is also the term used to refer to the technique used to create these blades.” – from Wikipedia
The Japanese term san mai loosely translates to ‘three layers’ or ‘three flat things’. However, the technique was not limited to Japanese blade construction. Threw out history, where ever high carbon steel was difficult to source, clever smiths devised ways to put the edge holding higher carbon steel at the edge and milder steels or iron in other portions of the blade. The san mai blade construction was one of the simplest approaches to this effort. As a side benefit, due to the materials of the time, san mai construction could create a blade far more resilient than the quasi homogeneous steel.
This is because before crucible steel, carbon steel was not the homogeneous material it is today. Once extracted from iron ore, the bloom resembled a sponge like mass of steel and iron. The bloom was then broken into bits and sorted by eye for carbon content. While some sorts had more classes, the simplest of the sorts would have been into two class: high carbon (edge material) and low carbon (jacket material). These bits of steel were then combined by forge welding according to class. The goal being to create homogeneous billets of the various materials.
To that end and to drive out impurities, these billets were folded and forge welded over and over. Each time some of the impurities were driven out and the carbon content was evened out. The forge welding temperatures helped both helped via carbon migration and reduced total carbon content by deodorization that occurs at high temperatures. Because this was not an exact science, san mai and other construction techniques were created to assist function that non homogeneous steel lacked.
Modern Crucible Steel
This is why even today, crucible steel retains an almost mystical reputation. You might be familiar with the debate over ‘true Damascus’ vs ‘pattern welded Damascus. This is a topic for another time. For this discussion, the aspect of this debate that matters is the difference between Wootz steel (what some call true Damascus) and pattern welded steel. Although this difference could be made visually apparent with polishing and etching techniques, the major structural difference is that Wootz steel is a crucible steel. Crucial steel is literally melted together. Forge welded steel is not nearly as homogeneous for obvious reasons.
The more homogeneous a steel is, the less the blade benefits from construction techniques like san mai and other lamination. This is why history sees fewer lamination techniques in cultures which developed crucial steel. It is also likely why crucible steel was highly prized. It was much easier to create a quality blade with a crucible steel.
Modern Steel is Crucible Steel
Although traditional Wootz steel also benefited from a certain combination of alloys which also provided its unique appearance, modern steel is crucial steel. Modern steel comes in a very homogeneous state. The modern knife maker can order steel in a wide range of very narrow specifications. When we order 1095, we know the carbon content of the steel is approximately .95%, we know the approximate alloy content, we know when properly quenched its hardness will be approximately 66 on the Rockwell scale. We also know the temperatures to temper the steel for various properties. Much of the guess work has been removed, so has the need for laminated structures like san mai or pattern welded Damascus.
So why create a san mai knife? For the same reason some paint realistic paintings when we have cameras. Because it is art. Today, virtually everything a person can produce by hand can be mass produced by machines. Those few things which can not be created by machine today will be possible in the future. What a machine mass production can not give you is the right and pride to say “I made that”. That is why we do it.
Easy Wrought Iron San Mai
Typically, san mai knives are forged using a gas forge, electric welder and hydraulic forging press. Fortunately for the knife maker on a budget, history tells us neither are necessary. Nor are modern or even period correct hammers or even tongs. Quality sam mai knives can be produced with a Harbor Freight anvil, standard ball peen hammer, and a coal forge.<p>