鮫皮（さめがわ）の柄下地加工技術——柄糸の下で滑りを止める伝統工芸

When you grip the tsuka of a Japanese sword, beneath the wrappings of cord or leather you feel a hard, grainy texture. This is the base material known as samegawa (ray skin). While the eye is drawn to the beauty of the tsuka wrapping, the single sheet of skin adhered beneath it actually has a major influence on the stability of the grip and the durability of the entire hilt.

What Is Samegawa—Stingray Skin, Not Shark

Although the name "samegawa" (shark skin) has become established, most of the material actually used is stingray skin. The skin on a stingray's back has densely packed small limestone particles that create a distinctive rough texture. The section in the center of the back where a single row of particularly large particles forms is called the oyatsubu (parent grains), and this has traditionally been the most prominent position in the design of the hilt. The hardness and arrangement of these grains is precisely what has made samegawa so valued as tsuka base material.

Function as Tsuka Base Material

The purpose of adhering samegawa to the tsukagi (hilt wood) is not merely decorative. First, the textured surface increases friction with the cord or leather wrapped around it from above, preventing the wrapping from shifting or loosening. Second, the skin itself serves as a shock absorber and protection for the tsukagi against impact and moisture. Third, it functions as a non-slip grip and maintains a certain degree of holding power even after the wrapping threads have worn thin. The beauty of the final tsuka wrapping is only achieved when this base material has been properly prepared.

Processing Steps

Samegawa arrives in a dried state and cannot be shaped to conform to the tsukagi while in this condition—it is too stiff. First, it is soaked in water and thoroughly softened to give it flexibility. Next, excess flesh and fat remaining on the back are carefully scraped away and the thickness is evened throughout. If this preparatory work is done carelessly, the skin is prone to bubbling or peeling after being adhered.

Once the samegawa has been sufficiently softened, it is cut to match the shape of the tsukagi and adhered smoothly using adhesives such as nikawa. Since the tsuka has a three-dimensional shape that envelops the nakago, when stretching the skin from a single flat sheet to conform to the three-dimensional form, skill is required to adjust the force carefully so as not to crush the grains. After drying, the surface is smoothed to remove sag and irregularities, and the preparation for wrapping with cord is complete.

The Design of Oyatsubu Placement

In the process of adhering samegawa, the craftsman pays particular attention to the position of the oyatsubu. It is considered traditional aesthetic practice to cut and position the skin so that the oyatsubu comes to the most prominent position in the center of the tsuka when held, and higher-grade mountings have always invested more effort in this placement. Even after the tsuka wrapping is covered with cord, the oyatsubu sometimes peeks through the gaps in the wrapping, and there exist designs that treat the samegawa itself as an object of appreciation.

The Rarity of Samegawa in Modern Times

Stingray skin used for samegawa relies heavily on imports, and there are times when it becomes difficult to obtain due to changes in catch volume and distribution. The higher the quality—with larger, more uniform grains—the rarer the skin, and securing the amount needed for a single tsuka is not simple. In recent years, alternative materials are sometimes used in place of natural skin for reasons of availability and cost, but in the world of traditional mountings, natural samegawa is still highly valued.

While the eye is easily drawn to the beauty of the tsuka wrapping's cord or leather, the processing technique of the samegawa that underlies it is equally an important step that determines the quality of the entire mounting. The TOUKENZA online catalog features various Japanese swords with different mounting finishes, so please pay attention to the craftsmanship of the tsuka and compare them.