Why is it so complicated to make a Japanese samurai sword?

I believe that no one is unfamiliar with the Japanese samurai sword, as it has been featured in many TV shows and movies. After all, the Japanese katana is considered one of the world's three most famous swords, and it's not really unusual for it to make a high number of appearances. Why are Japanese samurai swords famous all over the world? In fact, in the Tang Dynasty, Japan and the Tang Dynasty had a war, that is, the Battle of Baijiangkou, the Tang army's horizontal sword has the armor and flexibility of the Japanese soldiers wearing leather armor can not resist, the whole of Japan was in a panic.

Later, the Japanese recognized their own strength, in a humble way to learn from the Tang Dynasty, due to, Japan sent to the Tang Dynasty envoys there are a lot of craftsmen, these craftsmen to the Tang Dynasty to build the craft of the horizontal sword to bring back, and then to make the relevant improvements, which led to the formation of the later Japanese samurai sword.

The samurai sword is known for its powerful cutting ability, coupled with the rigorous forging process, making the Japanese samurai sword enjoys a very good reputation and reputation in the world. The raw material for Japanese swords is known as Tamahagane (たまはがね, Tamahagane). Tamahagane is made using a traditional Japanese method. This is a low-temperature steelmaking method, the furnace temperature does not exceed 1100 ℃, far from 1500 degrees Celsius, the melting point of pure iron, although the melting point of the ore containing impurities is much lower than pure iron, but at such a low temperature, iron ore is still difficult to melt completely.

The Japanese swordsmiths of the time, in order to obtain the ideal material and refine the impurities, used sand iron, which has a much larger surface area than the bulk of the ore, in order to melt the ore better, but at the same time, the time of refining became quite long, and it often required three days, three nights, or even seven days of uninterrupted smelting.

After spending a lot of time making a good furnace it has to be constantly fired with charcoal, and it must be refined at low temperatures, low temperatures to achieve the purest results. Put sand iron on top of the charcoal, and then another layer of charcoal, and then another layer of sand iron, layers overlapping, at different fires and temperatures for several days, at least three days and three nights in a row, and then in the morning of the fourth day will be dismantled smelting furnace, in the furnace to reveal a piece of bubbling seemingly molten lava object (26 tons of iron ore and charcoal consumed materials), at this time? Jade Steel? The smelter must choose which parts can be sent to the knifemaker to be made into knives.