The Technique of Fukurin — A Metalworking Tradition That Protects and Adorns the Rims of Tsuba and Tōsōgu

What Is Fukurin — The Metalwork That Wraps the Rim

Fukurin is a term referring both to the technique of wrapping the outer circumference (mimi) of tōsōgu — including the tsuba — with a thin, hammered-out metal band, and to the band component itself. Iron-ground tsuba and tōsōgu with thin rims made of brass, shakudō, or similar metals are prone to chipping and wearing along the rim through use and age. Fukurin reinforces this weakness while also serving a decorative role, presenting a metal of a different hue from the base plate as a border accent. It is a specialized technique within tōsōgu making, combining practicality with design sensibility, dedicated specifically to finishing the rim.

Beyond the tsuba, fukurin may also be applied to fuchi-kashira, kozuka, kōgai, and many other tōsōgu that have a mimi along their outer circumference. The purpose is the same in every case: to protect with a metal band the contour areas most susceptible to damage from daily drawing and sheathing and from contact while wearing the sword, while also functioning as a finishing detail that draws the overall design together. No matter how intricate the motifs or sukashi of the base plate itself may be, if the rim is chipped or distorted the overall impression of the piece is diminished. Fukurin is, so to speak, the technique that forms the "frame" of the work.

The Shapes of Fukurin — Maru-fukurin and Hira-fukurin

Fukurin is classified into several types based on cross-sectional shape.

• Maru-fukurin — a shape that wraps the rim with a rounded, raised form; it feels gentle to the touch of the hand or fingers, and conveys a soft impression aesthetically as well
• Hira-fukurin — a shape that wraps the rim with a nearly flat cross section, resulting in a thinner, more restrained finish
• Ko-fukurin — a narrow fukurin used for the purpose of reinforcing only the rim without drawing undue attention to it

Which shape is chosen depends on the material and design of the base plate, the preferences of the client, and the stylistic conventions of the metalworker's school that produced it. Even for tsuba with the same motif, the overall impression changes significantly depending on whether fukurin is present and what shape is used. A thick fukurin conveys a visually imposing impression, but it also affects the overall weight balance of the tsuba, so when finishing the piece as a practical sword mounting, craftsmen were required to judge whether to prioritize design or weight.

The Status That Materials Convey — Brass, Suakagane, Silver, and Gold

The metals used for fukurin are by no means uniform. The most common are brass and suakagane (unalloyed copper), which were widely used as relatively accessible materials that create a color contrast against iron-ground tsuba. Silver fukurin and "kin-fukurin" (gold fukurin), on the other hand, were often treated as finishes indicating a higher level of formality, and tended to be applied to formal koshirae or to a sword intended as a gift or for ceremonial use. The difference in materials goes beyond mere preference for color; it also serves as a clue for inferring the social context in which the tōsōgu was situated — for whom it was made, and in what kind of setting the sword would be used. There are finishes that combine a rough iron-ground tsuba with brass fukurin to aim for a contrast of hard and soft, and others that add kin-fukurin to a shakudō-ground piece to emphasize formality; the combination of materials itself was an expression of aesthetic sensibility — a point that must not be overlooked.

Wrapping the Rim — The Process of Fitting Fukurin

The work of fitting fukurin begins with hammering out the metal to be used into a thin, band-like strip. As the metal is hammered out it hardens and tightens, so annealing is interspersed along the way to restore softness, while the band is shaped to the necessary width and thickness. The basic method of fitting is to align this band along the mimi of the base plate of the tsuba or other piece and press it firmly, exploiting the malleability of the metal itself to clamp it around the rim. It has traditionally been the practice to fix the band using only the force of the metal being cinched tight, avoiding joints such as brazing, and after fitting, the rim edges are carefully filed and polished so that any steps are not conspicuous, finishing so that the boundary between the base plate and the fukurin flows smoothly and continuously. For tsuba whose base-plate mimi is not a perfect circle, or tsuba with intricate contours created by sukashi carving, even aligning the band with uniform force is difficult, making it a painstaking process of gradually shaping section by section while adjusting the pressing strength in each area. The precision of the finish is judged by whether any slight gap or lifting has formed between the fukurin and the base plate, and a fitting that is less prone to loosening over time has been considered the mark of good craftsmanship.

Fukurin as a Clue for Appraisal

Fukurin is at once a decorative and reinforcing technique and one of the clues used in appraising tōsōgu. The presence or absence of fukurin, the cross-sectional shape, the width, and the type of metal used are all elements that reflect the tendencies of different periods and schools, and together with the design of the base plate itself and the highlights of the jigane, they serve as material for reading which school's work a given piece represents. The depth of fukurin as a technique lies in the fact that a single small border strip encapsulates within it the craftsman's style and the tastes and formal standing of the owner who commissioned it. When appreciating tōsōgu — where one's eye tends to focus solely on the quality of the motifs and sukashi of the base plate — taking the time to examine carefully the fukurin running around the rim will often reveal, for the first time, an attention to detail in the craftsman's work that one had not previously noticed. The view that it is precisely in the unshowy parts that a craftsman's skill tends to manifest is a perspective common to Japanese traditional crafts, not limited to fukurin alone.