The classic nihontos that appeared during the mid-Heian to the earlier Kamakura era all featured a deep and prominent curve. This was necessary since these were mainly utilized for slashing and attacking opponents on horseback. Yet when it came to the swords that appeared during the more peaceful times in history, like during the Shinto times, the swords turned out to be more ceremonial than utilitarian; also, the arch of these blades were also very slight.
Sori is known as a type of curve that appears on a traditional nihonto and this can be found by finding the deepest portion of the arch; this is along the mune, between the munemachi and the kissaki’s extreme tip. Usually, it is subtle and difficult to classify but the sori is a vital factor when it comes to kantei (appraisals). Although the jokuto-tachi featured a slightly evident curve, it was often uchi zori or had an inward direction. A regular outward curve was usually created by accident but the curve of a nihonto was definitely made this way to achieve this appearance. This curvature or sori mainly results from the process of tempering a sword that is made with a ridge line which is close to the back portion of the weapon; it also features a wider temper line compared to the usual jokoto blades. The actual arch is made by the distinctness in shrinkage that can be seen along the cutting edge compared to one that’s seen along the back. It is a natural curve that has been developed by skilled swordsmiths, incorporating this to the elegant sori of the nihontos.
To determine the sori types of specific nihontos, a line is created to measure the nagasa (length) to the sword’s mune. If the sword features even a slight curvature, the length of the longest line amid the mune and the nagasa line is referred to as the sori; this will then be at the point wherein the sword’s curve will be at its maximum.
The Different Sori Types
The sori of a classic nihonto is categorized from the pre-Heian chokutos which are basically the straight swords; the degree of the sori right at the point where the deepest curve can be seen varies depending on the period in which the piece was forged. With that, it can be said that the sori is a great indicator of the date when a sword was crafted. The sori is also classified into one of the following:
- The Koshi Sori – Bizen Sori
Koshi translates to waist and this refers to the deepest portion of the curve that is close to the sword’s waist that is forward of the machi; this area is also where the blade connects with the tang. It is also referred to as the Bizen sori since a lot of the Bizen schools utilized this specific form. Most of the earlier Bizen blades, as well as those from the late Kamakura period, featured the Koshi zori; additionally, the tachi crafted between the Heian and mid-Kamakura era were usually the koshi zori.
- Torii Sori – Kyo Sori
This is the deepest portion of the curve located at the blade’s center. This specific form is named after the Torii which is specifically the entry to a Shinto shrine which also greatly resembles an arched crosspiece. The inmost point of the torii sori coexists with the blade’s halfway point.
- Mu Sori – Chukan Sori
Mu translates to no or none and a blade that features the musori is generally a blade with little to no curvature; it may also have a mu zori or none at all. The tanto is one of the weapons that commonly feature the mu zori and during the thirteenth and fourteenth centuries, there was a slim type of tanto that was quite popular among individuals. This tanto was described by not having a mu zori or curve and its length was somewhat shorter compared to the tantos from the later periods. The term is also utilized for tanto blades without the sori. Chukan means middle and specifically refers to the musori located between the uchisori and sori.
- Saki Zori
This is the most common curve seen on the Naginata; the deepest portion of the curve is amid the blade’s center and tip. The sori can also be seen in a couple of swords that were crafted during the early Muromachi era.
- Uchi Zori
Uchi translates to inward or inside so when the blade curves the opposite way or specifically towards the edge, it is then referred to an uchi zori. Tantos that were crafted during the Kamakura era commonly displayed this. The uchi zori is an extremely slight curve that goes towards the cutting edge; when the tanto features an uchi zori and really has no fukura, it will look just like a bamboo shoot and is called the takenoko zori.