The blade material of 3 layers with the original thickness of 20.0 mm has been thinned to the final thickness of 2.0 mm by rolling processes repeatedly applied. Tamahagane is the root of the Japanese Samurai Sword. The name was used only on very high quality swords. "San" 3-Ply steel blade is made by repeated rolling and trained many times. This way Tamahagane is produced in an ancient way with the modern technique. By repeated rolling, all impure materials in the alloy are extracted from the material and the blades become harder and more durable. - (out of the knife description brochure)

Personally I wonder how often such a knife has to be sharpened. The sharpening angle for this knife is described as "14 - 15 degrees".
And secondly I wonder if ancient Samurai sword blades received a lot of scratches? Considering that these swords had to cut through bones, considering sword fights, the swords must have looked like a mess after years of eager and happy usage.