Tangdao first made two pieces of hard steel by folding method, the temperature was controlled at 750-800 degrees, and the folding times were about 15 times, with 32,768 layers. Then two pieces of 32,768-layer hard steel are used to sandwich a mild steel, heated to about 1 300 degrees, forged and then stretched. At this time, because the steel knife has been heated to 1300 degrees, the surface has been decarburized and the hardness has become smaller. Therefore, it must be carburized to enhance the surface hardness. This technique seems to have been lost now (but in recent years, Zhou Zhengwu, a descendant of Longquan Sword, claimed to have restored it). After quenching, it is shaping, grinding and polishing, which is the traditional famous three-piece combination. Japanese Dao is made of a piece of jade steel, just like the hard steel in tangdao. After being made, it is made into a steel block of about 20 cm. Open a V-shaped groove on the side where the back of the knife is to be made, and the depth is one third of the whole steel. Then put a piece of mild steel in it. At this time, the steel is heated to 750-800 degrees and made into the shape of a knife, just like folding forging. After that, cover it with soil and burn it. Japan has covered the soil many times, each time it is very thin and layered, so Japanese knives have very obvious sea lines and knife lines. This is not the pattern of folded patterned steel, but the real folded patterned steel, because there are many layers, so it is not obvious, and only the naked eye can see it very carefully. Tangdao is soft inside and hard outside, while Japanese knives are sharp and hard, with high back toughness. If the blades of tangdao and Japan collide, a Japanese knife is one.

In short, the blade is soft inside, hard outside and tough in the middle, with uniform counterweight and fine grinding, which can be described as a good blade.