As in any country, not all Japanese of the top social caste were necessarily wealthy. Towards the end of the feudal era in Japan poor and even destitute Samurai did exist. Many Samurai were just making ends meet and only a few Samurai could afford a sword of high quality. While a low to medium grade Japanese sword was still a marvelous piece of technology for its time it was the finer swords which were truly amazing.
In forging a Japanese sword the master would crouch on one knee at the anvil, holding the red hot billet with tongs in his left hand and strike it with a hammer in his right hand (Japanese of any social standing, had they been born left-handed, were forced to become right-handed). During the forging process there were three apprentices standing around the anvil – one opposite the master, and one on either side. When the master struck the billet they would, in sequence, strike the exact same spot on the billet with larger, two handed hammers.
While common Japanese swords were forged from a single billet, the best quality blades were composed of separate billets of different composition, forge welded together for the end product. Usually this was done with two billets, each having started as a piece of iron forged to a piece of steel, heated, folded over on itself, then hammered together. This folding and hammering process was repeated many times to create thousands of layers within the width of the billet. Two of these iron-steel multi-layered billets would be forged to a pure steel billet between them, then forged into a sword blank. This resulted in a sword having a body of layered iron-steel with a center core and cutting edge of pure steel.
A blade forged like this, when heat treated, would have layers of iron which were still flexible while the layers of steel would be more rigid, resulting in a blade which is much more difficult to break. In addition, forging a blade in this way would align the steel molecules more uniformly while driving out inclusions (microscopic spaces or impurities) resulting in a harder and more rigid material with less tendency to break or crack.
But that’s not all. Japanese sword makers had a unique process for quenching blades which was the same for all Japanese swords. When the sword had been forged, shaped, and ready for heat treatment it was covered in a layer of clay mixed with ash. This layer of clay was about one quarter to three-eighths inch thick. After application of the clay, before it dried, the clay was scrapped off the part of the blade which was to be the cutting edge. When the blade was heated then quenched in water the exposed edge cooled quicker than the body of the blade, making the steel at the edge much harder than the rest of the blade.
When this quenching process is used the difference in hardness shows up when the blade is polished. The body of the blade, being relatively softer, comes to a brighter shine while the harder edge is still duller. In fact, a Japanese blade polisher (not the same as a blade maker) will apply a slightly courser grit to this harder edge area to highlight this difference. The result is a blade with a very high polish on most of the surface with a cloudy finish on the area at the cutting edge.
It was known that meteorite was prized by Japanese swordsmiths for use in making their blades. I have also read that some swords tested with modern equipment have been shown to have chromium in the steel. I have no idea how a feudal era Japanese swordsmith would find and identify natural examples of chromium and then blend it uniformly into a steel billet. I can only assume they had an empirical understanding about how some ore looked different and how that related to the end product.
In the late 13th and early 14th century lived a man by the name Masamune who is regarded as the finest Japanese swordsmith ever. In his own lifetime his blades were so highly regarded that after one point he would no longer sign them (Japanese swordsmiths sign their blades on one side of the tang using hammer and chisel) believing that if a person could not recognize the quality of his work that person didn’t deserve to know who made it.
While blade testing in Japan was not particularly common there are known historic examples of this practice. One test involved securing a blade of average quality in a solid fixture and cutting it with the blade being tested. To pass this test the superior blade should not show any nick or crack where it cut the other blade.
Another testing method involved cutting through human bodies. In some cases this was done while executing a convicted criminal. A superior Japanese blade was expected to be able to cut diagonally through a human torso from one shoulder, through ribs, spine, and on through the ribs on the opposite side without damaging the blade. In one legendary case I have read about the blade had the inscription “five body sword” on the tang opposite the maker’s signature. Legend has it that this blade had cut through five stacked human cadavers in a single stroke.
75 years ago US troops fighting the Imperial Japanese in the Pacific often faced Banzai charges of massed troops, some with little more than rifle-mounted bayonets and swords after running out of ammunition. In fact, there was a training film shown to some Imperial troops which described how to disable an American machinegun with the stroke of a sword in which a sword expert did just that with captured American equipment.
During WWII and the following occupation of Japan many Japanese swords made their way to the US – a number of them true museum pieces. There still are some significantly valuable Japanese swords in the US market but you can expect that the best examples of them have already been identified and repatriated to the much higher priced market in Japan. Should you happen to possess or find one and wish to have it reconditioned please understand that only a person properly trained to polish Japanese blades will be able to do the job without seriously detracting from its value. This is a very expensive proposition and only worth it if you have a blade of exceptional value. Any collector can immediately tell the difference between a blade which was polished by a traditionally trained polisher and one which was polished with modern equipment.