Here I want to give you a quick history lesson. Most iron deposits in Japan contain ore with very high carbon content. This iron was called Tamahagane or pig iron. This carbon content would make every sword break extremely easily. So, the Japanese swordsmiths had to come up with a solution to this problem. They discovered the process of folding steel. Every time the steel is folded you create more and more overlapping layers.
These alternating layers greatly enhance the toughness of the blade. Furthermore, they add to the unique design of a katana. Everyone can spot a katana by one of its prominent features, one of it being the layers created by the folded steel. Ok, this is the part where it gets tricky. However, I think I came up with a great explanation for this process. You start with a single layer. When folding it once you have two layers. Folding again results in four layers. The next time you fold the paper you have 8 layers, 16 layers, 32 layers, 64 layers and so on.
The same principle applies to folded steel. After folding a blade 10 times you have layers. Folding 16 times results in 65 thousand layers. This is the reason why people say their katana is folded times. Those people are confusing the number of folds with the layers created. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them. M y grandmother to tell me that if I burned my finger, I should dip it in a cup of tea.
She knew that, long before doctors knew anything about the healing power of the tannic acid in tea. Now my grandmother was a fine intelligent woman, but she didn't know organic chemistry. The art of Japanese Samurai sword making is like that. It reached an astonishing level of perfection as early as AD -- years ago. A Samurai sword is a wonderfully delicate and complex piece of engineering.
The steel of the blade is heated and folded and beaten -- over and over again -- until the blade's formed by 33, layers, forge-welded to one another. Each layer is a hundred thousandth of an inch thick. All this is done to extremely accurate standards of heat treatment. The result's an obsidian-hard blade with willow-like flexibility. These blades represent a perfection of production standards that modern quality control hasn't matched.
Yet the Japanese craftsmen who made them didn't know anything about temperature measurement or the carbon-content of steel. How do you suppose they repeated such perfection? Coating the katana While the katana's body is now complete, the swordsmith's work is far from over.
Just prior to firing the sword a final time, he paints a thick, insulating mixture of clay and charcoal powder onto the blade's upper sides and dull back edge, leaving the sword's sharp front edge only lightly coated. This serves both to protect the blade and to give it its signature wavy design called the hamon , which later polishing will reveal.
Curving the blade Next, the smith pulls the katana from the fire and plunges it into a trough of water in a rapid cool-down process called "quenching. The difference in both the degree and speed of contraction between the two forms of tamahagane causes the sword to bend, creating the distinctive curve. This is a tricky stage, in which as many as one in three swords is lost.
Polishing the blade The katana, fully forged, now goes to a skilled sword polisher, who may spend more than two weeks honing the sword's razor-sharp edge. Sometimes called "water stones," these tools are typically composed of hard silicate particles suspended in clay.
As the clay slowly wears away during use, more silicate particles are revealed, guaranteeing excellent polishing quality throughout the life of the stone.
Each consecutive set of polishing stones contains finer and finer silicate particles and removes less and less of the steel. Adding final touches In the final stage, metalworkers add a decorated guard of iron or other metals at the sword's hilt.
Next, carpenters fit the weapon with a lacquered wooden scabbard, which artisans then decorate with various adornments. Fashioned from gold or exotic leathers and stones, the katana's handle is as much of a work of art as the blade itself.
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