Impurities

 

Watching a Japanese samurai sword (刀, katana) is one of the finest pleasures you can experience.  Especially when you learn about the process that is needed to make one.

The steel used to build one is called Tamahagane(玉鋼) and consists of several layered steels with different carbon concentrations. This steel is full of impurities and the look of it in the beginning of the process is not very nice.

The antiquity of the steel is very important in the process of removing those impurities.  The oldest the steel, the highest concentration of oxygen making it easier to get rid of the impurities during the hammering, thus resulting in a stronger blade.

High and low carbon steel are welded and folded several times and the hammer and fire make their hard work to get rid of impurities in a very strenuous and long process where each element makes its part in forming a stronger and stunning blade.