The thing about Nihonto that most impresses collectors, experts, martial artists, and simple admirers alike is their incredible strength, durability, and edge-holding ability. The secret behind a Nihonto's strength is the Japanese smiths' method of forging the blade. Steels of different properties are laminated together, each steel's strength canceling out another type's weakness as its own are canceled by the qualities of the others. Numerous new lamination techniques have been introduced over the years but, as is often the case with a very refined art form, the methods still in practice from centuries earlier have usually proved to be the best. A Nihonto's value is partly determined by the complexity of the lamination used in its construction. The combination of the laminated steels and the heat-tempering of the blade to give it a hard edge (hamon) renders the finest Nihonto virtually unbreakable.
The lowest-grade blades are of the Maru kitae, or unlaminated, variety, composed entirely of Hagane (hard steel). While this might strike the novice as an advantage, in reality it is a lethal shortcoming: Hagane is brittle. The blade would be able to be sharpened almost limitless times but it would also likely develop severe stress cracks, even break outright, as it saw use in combat. This was a problem that often plagued the lower-ranking samurai, as they could not afford weapons of higher quality than Maru-kitae.
The Kobuse, Makuri, Wariha Tetsu, and Gornai kitae are all two-metal lamination techniques. Kobuse kitae was the technique used on most WWII-era nihonto; it involves laminating a thick layer of Hagane in a