MARUDOME 棒樋に添樋・丸止めThis is a straight groove with a smaller parallel companion groove (soe-bi) below the shinogi line. “Marudome” means that both grooves stop above the nakago on the polished portion of the blade and are finished with rounded ends. The soebi runs the length of the blade, but stops before the yokote line and the point.
GROOVE-END SHAPES
4. BO-BI with TSURE-BI/
KAKUDOME 棒樋に連樋・角止め
This is a straight groove with a smaller parallel companion groove. However, in this case, the second groove (tsure-bi) runs beyond the bo-bi near the point of the sword and extends into the shinogiji surface ahead of the larger bo-bi. Both grooves are finished with kakudome, a square end that stops the hi in the polished area of the sword above the nakago.
5. FUTASUJI-BI/KAKUDOME 二筋樋・角止め
Futasuji-bi are twin parallel bo-bi. “Kakudome” means that the grooves are finished with square ends, stopping just above the nakago.
6. NAGINATA-BI with SOE-BI/MARUDOME
薙刀樋に添樋・丸止め
Naginata-bi, the grooves seen on pole-arms (naginata) and sometimes on tanto and katana (as shown here), have a characteristic design. A large bo-bi is finished with a marudome (rounded) end above the tang. The forward end of the bo-bi has a distinctive shape: the side of the hi closest to the cutting edge extends beyond the upper part, so the leading edge of the hi forms an arc. Matching this curve in the forward end of the hi, the upper surface of the blade (shinogi-ji) is beveled sharply toward the mune edge; this beveled surface extends all the way to the tip of the point. A longer soe-bi (companion groove) runs below the bo-bi and extends beyond its leading edge below the beveled part of the shinogi-ji.
BOSHI: THE SHAPE OF THE HAMON ON THE POINT
The boshi is the hamon in the point area. There are a number of styles; individual smiths and schools used characteristic boshi. Schools also changed their boshi styles in different eras.
Three different styles of sword with different points are shown on this page.
At left is a hira-zukuri blade. It has flat sides and no defined point area. The blade has a flat surface from the top of the tang to the tip.
At center is a shinogi-zukuri blade. The point area is defined by the yokote line separating the point area from the body of the blade.
At right is an osoraku-zukuri tanto. It has a very large point that covers about half of the blade’s length. The point area is defined by a yokote line, and is polished to contrast with the body of the blade.
EXAMINING THE HAMON
One of the most singular features of the Japanese sword is its hamon, the visible pattern of the hardened edge. After forging, the swordsmith coats the sword with clay, heats it, and then quenches it in water to produce the uniquely patterned edge. The hamon, which is composed of a form of steel called martensite, is far harder than the body of the sword. A properly made, functional Japanese sword must always have a hamon.
The hamon depends on the condition of the sword. If a sword is in poor condition, or has an old polish, or has been polished many times over the centuries, the hamon may be nearly or com pletely invisible. It may even be absent altogether.
Even if the hamon is in good condition and the sword has a good polish, the hamon might be difficult to see and appreciate. As mentioned earlier, the sword must be clean, examined under the proper light, and held at the correct angle relative to the light, with the sword pointed just below the focused light source. Under these conditions, the line defining the hamon will be visible near the reflected light source on the blade.
Due to the significance of this feature, a person who is interested in Japanese swords should be aware of certain characteristics that the hamon possesses. It will usually have a well-defined boundary (nioiguchi or habuchi) that sets it off and makes it clearly visible against the body of the sword. There should be no gaps or breaks in the boundary line that defines the hamon, and this line should be present throughout the length of the blade, with no faded or weak areas. In addition, a good hamon does not usually have a simple shape or boundary, but contains a complex pattern and numerous details.
A hard, sharp cutting edge is required for a sword to be functional, and the complex structure of the hamon developed in response to this need for functionality. The oldest Japanese swords, which date back to approximately the fifth or sixth centuries, are straight, with narrow hamon. The older hamon were basically a straight band of brittle mar tensite steel running along the cutting edge of the blade. Although a sword made completely of brittle martensite would cut well, it would suffer a large amount of damage in use. Therefore early smiths made the body of the sword from much softer forms of steel called pearlite and ferrite. These gave the sword flexibility and toughness, so that it could bend to some extent without breaking. The design of the Japanese sword uses the particular properties of several forms of steel in different parts of the sword to make a functional, effective, and enduring weapon.
To examine a hamon in detail, the sword is aimed near or below a point light source, so that the details of the hamon can be seen by looking near the light reflected on the blade. As this only allows inspection of a small area, the sword must be moved continuously to examine the entire hamon.
As swords evolved over the centuries, they became larger and acquired curvature; the hamon also become wider and more complex. This change in the hamon developed for a very good reason. As noted above, the simple straight hamon of the earlier swords consisted of a band of hard martensite steel bonded together with a softer steel body in a straight line along the entire length of the sword. Because of the differences in the properties of these two types of steel, sometimes a single blow or strike could cause most of the narrow martensite cutting edge to separate from the body of the sword.
In response to this, swordsmiths learned to make more complex and wider hamon consisting of a series of semicircles or waves, often varying in width and height along the length of the blade. The visible boundary defining a complex hamon can range over the width of the blade from the upper part to the center, and down almost to the cutting edge. The hamon can be described as resembling a series of teeth. These “teeth” make the physical boundary between the martensite edge and softer sword body effectively much longer, and interlace the different types of steel present in the edge and body of the sword. Thus the cutting edge is bonded firmly to the body of the sword with an almost zipper-like structure. Complex hamon also limit the size of chips in the cutting edge and damage that can occur during use.
These hamon were first seen in Japanese swords from around the eleventh and twelfth centuries, and were further developed through the twelfth and thirteenth centuries during the Kamakura period (1185–1333).
