1) Let’s start examining the sugata or shape of the blade. The shape should appear strong, the curvature natural and the kissaki should be in proportion to the width and length of the blade. Take note of the mune or back edge’s shape and height. Hold the blade at upright at arm’s length when examining a blade’s sugata.
A great deal of information is imparted on the sugata about the age of the blade and sometimes about the area in which it was made. On the other hand, there is a fair chance of the blade having a good quality if it has a good shape and sits comfortably in the hand. It is impossible for a good sword to have a bad shape unless it has been altered, damaged or repaired in some way. This frequently happens to swords thus it is important to try and imagine the ubu or unaltered shape of the blade.
2) The next area to study is the hamon. This is most often referred to as the “tempered” edge. This is where the sword has been quenched to provide a high carbon steel area which will hold a sharpened edge. It will be seen in contrast to the entire body of the sword.
The hamon may be in an infinite variety of patterns, but appears as a milky white color on a properly polished blade. The upper edge of the hamon should be formed from tiny martensite crystals called nie. There are cases when these are too small to see with the naked eye and are then known as nioi. It is nie and nioi that border the hamon and form its pattern.
The ideal way to get a good examination is to hold the blade at an eye level ideally pointed towards a spotlight. The nioi-guchi or line of the hamon should form an unbroken and constant line from the machi area or bottom of the blade along its entire length. Watch out for a serious flaw of a break in the hamon, called nioi-giri. It is also important that the boshi (the area of the hamon within the kissaki) does not disappear off the edge. This is also a serious flaw in the blade and is only acceptable on great swords of historical and cultural significance! No compromise should be accepted here.
3) If sugata and hamon pass muster, the sword is acceptable. Look carefully for any signs that show the sword hand forged and cleverly mass-produced piece such as Showato during World War II. This assurance is done when you examine both the jigane and jihada. The jigane is the actual steel from which the sword is made and might show subtle change color and texture. The jihada is the surface pattern of the jigane caused by the forging process and emphasized by polishing. This is mostly visible between the edges of the hamon and the shinogi, or ridge line. The jihada, appearing like a wood grain, is described by its type and size (i.e., ko-mokume=small burl) although there are many criteria for judging the quality of the jihada. Basically, ascertain if the jihada is present then it is enough to say that the sword is at least a hand-forged blade.
4) Carefully look for any obvious flaws or faults of the sword. There are some of these that may be more acceptable than others basely dependent on the age of the blade. Put simply, a 12th-century blade is entitled to have a few problems that would not be tolerated in a modern sword. However, all faults and flaws obviously detract from both the beauty and expected value of a sword.
Signs of holes or bubbles in the sword may indicate air or impurities that have been created in the forging process commonly found just under the surface of the blade. Also check the ha-saki or cutting edge very carefully for hairline vertical cracks running from the ha-saki into the hamon called ha-giri. Ha-giri are very serious flaws because if the sword were used to cut, the ha-giri would bend or break. Ha-giri are obviously considered unacceptable under any circumstance.
5) Finally, do an inspection of the nakago or tang. The nakago on a good sword will always be carefully finished. The patination should be of good color and the rust should not be cleaned off under any circumstances. If there are any inscriptions these will be of interest. A good mei will be skillfully and confidently written in contrast to an untidy, jumbled, or hesitant inscription. It would not matter whether you can read the inscription as most modern Japanese cannot read the old Kanji in sword inscriptions, so long as it looks confidently and evenly executed.
Lastly, avoid making this costly mistake. The most commonly encountered swords in the West are the previously referred to, Showato. These blades were made in the Showa period (1926-89) when a vast majority was mass-produced for the Imperial Army and Navy during the Pacific War period. These swords are not considered as true Nihonto. Showato are seen as a symbol of Japan’s recent militaristic past since they are still illegal in Japan. Showato is reasonably easy to recognize from their small stamps on the nakago (usually Seki or Showa). They are often signed with untidy and loosely carved characters. An unsharpened inch or so of blade (known as ubu-ha) is found just above the habaki where heavy and clumsy swords are usually found in Gunto (army) mounts. Mostly they appeal to military sword collectors and may not appeal for Iai practice or the serious study of Japanese art swords.
You will understand from the above that there are many subjective judgments to be made when judging a Japanese sword blade. There are many other fine details in both jihada and hamon known as hataraki or activities which add greatly to the beauty of the Japanese sword, however, detailed explanation of these falls beyond the scope of this article.
The next step is to find out to which of the Gokaden it belongs; as a reminder:
Yamashiro = Mokume-hada, Suguha in Nie
Yamato = Masame-hada, Suguha in Nie
Bizen = Mokume-hada, Chôjiba in Nioi, Utsuri
Sôshû = Mokume-hada, Midareba in Nie
Mino = Mokume-hada, Midareba and Togariba in Nioi