Forging a Japanese sword is quite a complex craft. No wonder that there are so few skilled sword smiths that can forge Japanese swords in the traditional manner. BushiSwords only works with very experienced sword masters who have gained lots of respect for their work.
In the old Japan, sword smiths produced folded steel blades. The best and most expensive blades used lamination. Monosteel was not used back then. Reason for this is that carbon steel in those days was of very poor quality. The carbon was not distributed evenly and a monosteel blade would be very unreliable with harder and softer spots in the blade. Therefor sword smiths had to fold the steel several thousands of times to get an evenly distribution of carbon in the blade.
Today the quality of carbon steel is very good and carbon is evenly distributed in the steel. So it is not necessary to fold a blade to make it strong. But if you want a Japanese sword that is traditionally made in all aspects, you will choose a folded blade anyway. Perhaps you will even go for a kobuse lamination blade.
Kobuse blades are folded steel blades that have a very hard 1095 carbon steel core and edge, and softer 1060 steel sides and back. This construction gives your Japanese sword even more flexibility to handle the impact of the cut.
The steel is hammered into the basic shape of the sword. If a sword is folded or even has kobuse, the parts are forge welded together. But they retain their differences in hardenability.
When the sword is forged, it will be heat treated. This does not happen with uniformity throughout the blade, like European swords do. BushiSwords are always differentially tempered with a traditional clay method. If steel cools quickly, it becomes very hard, but also brittle. If it cools slower, it is softer but more flexible.
To combine the benefits and get a hard cutting edge and a flexible back, the blade is painted with clay. A thin layer or none at all is painted on the cutting edge. This part will cool quickly and becomes very hard. A thick layer is applied to the rest of the blade and cools much slower causing it to become softer and more flexible. This way your BushiSwords katana or iaito will have a strong edge and still will be flexible enough to handle the impact of the cut.
The clay mixture is a well kept secret that needs to be just right. It contains clay and coal ash among several other ingredients.
When the sword is quenched, the uninsulated edge contracts, causing the sword to bend towards the edge. Because of the insulation, the sword spine remains hot and pliable longer, but then contracts more than the edge. This helps the sword smith to create the curvature of the blade. This process also results in a hamon or the tempering pattern. The various hamon patterns result from the manner in which the clay is applied.
Two holes are made in the tang. A mekugi bamboo pin in each hole will fix the handle to the tang. the bo-hi (groove) is also created now (if you want it ofcourse). It is often called blood groove, but it does not allow blood to flow from the blade. It is meant to reduce the weight of the sword while keeping structural integrity and strength.
The blade is now ready to be polished to improve the shape of the blade as well as to make it more beautiful. Polishing is done with seven types of stone. This is a very time consuming process.
Finally the different mountings such as the tsuba, menuki, wrappings and more are mounted on the blade. Last but not least a saya (scabbard) is made that fits your sword perfectly.