Process of Carving & Shaping a Tanto Saya
Once the tsuka is made, it is time to create a saya (scabbard) for the blade. The saya should fit snugly on the habaki, with most pressure to the top and bottom, and should hold the blade securely without rattling or jamming. The lines and proportions must be appropriate to the blade and handle and take into account the appearance of the whole unit.
Similar to the process for tsuka, a saya is shaped in two distinct stages, first the wood is split and the inside carved to receive the tang, and then it is joined back together and the outside is carved, planed, and shaped. As with the tsuka, the edge of the blade is placed slightly off centre in the block so that the edge is fully supported by wood rather than resting against the glue joint.
Carving the Inside
Creating a saya is begun by selecting an appropriate block of wood, sawing or splitting it into halves, and carving out each half to guide the blade smoothly. Carving is done with purpose designed chisels called saya-nomi (鞘鑿). The mune should be centered in the block of wood but the small flat surface for the edge should be fully seated in the omote half of the wood, slightly to one side. The purpose of this is to align the wood with the tsuka and keep the edge from splitting the glue joint if it ever makes contact with the saya.
Beginning with the omote, the carving begins at the mune and moves to the ha, checking the fit of the blade without the habaki. Once the omote fits well, the ura is carved from the mune to the ha, checking carefully and often. Finally, with the habaki in place, the halves are carved again to form the habaki area and tune the fit carefully. When the fit is just right and the blade sits in place, the two pieces of wood are joined back together with sokui (rice paste glue) and wrapped tightly with a cord until dry.
Shaping the Saya
The outside work is carried out using chisels, planes, and occasionally coarse files. The block is first squared up and then taken down to the rough dimensions. The shape of the koi-guchi (saya opening) is marked and carved and then the rest of the block is chiseled down to meet it. A plane is used to smooth and true up the surface and final sanding is done with tokusa (horsetail plant, equisetum hyemale, 砥草, “to” as in togi) glued to wooden blocks with sokui (rice paste glue).
Usually a horn or metal reinforcement is added to the koiguchi to counteract the pressure of the habaki and prevent the blade from cutting through on a rough draw. Horn is tough but not as hard as bone or metal. It can be carved with chisels or knives and has a grain-like structure to it. The method for the koiguchi is to carve away enough wood for the horn or metal to sit in its place. The habaki is used as a rough guide for making the opening in the horn, a kiri used to drill holes and then files to create the shape of the guchi.
Kurikata translates “chestnut shape” and in its basic form is the tying off point for the sageo (cord) that attaches the saya to the obi (sash/belt) so it stays in place on a draw or slip down when wearing. They are often made of horn but can also be metal or sometimes wood depending on the type of knife.
Depending on the design and material, nikawa (膠, にかわ, natural hide glue) or kusune (薬練, くすね, pine resin glue made from matsuyani), or sometimes a mixture of sokui and urushi (nori-urushi) is used to fix these parts in place once the final lacquer work is finished.
Shitaji, Preparing the Lacquering Foundation
There are two distinct stages to using urushi (traditional Japanese lacquer, made from the sap of a tree). The first stage is to prepare the base material by sealing, filling, and polishing, and the second is to coat with a smooth finishing layer. Urushi is used in several ways to prepare the surface, first by coating and wiping off, known as fukiurushi, and also as an adhesive and gap filler when blended with other materials such as sokui (rice glue) and finely powdered clay and earth.
Each time a layer is added to the foundation from one to three days are required for curing, and then the surface is wet polished and dried overnight before adding the next. The goal is to seal the surface and fill in any low spots so the final layers of urushi goes onto a smooth and even surface.
Urushi, The Final Layers
There are several approaches to applying the final layer, depending on the desired finish and the style and skill of the artisan. One way of achieving a smooth surface is to paint the last layer thicker than the foundation and middle layers and allow the urushi to settle out into a glossy surface. The other is to polish the final brushed layer and then apply several coats of fukiurushi followed by a fine oil polish. Textured surfaces such as ishimeji (stone surface) can be created by various means but the most common is to sprinkle finely powdered and screened urushi or charcoal onto a wet layer of urushi and then overcoat to seal it after curing.
Each time a layer is added to the surface in the final stages, from a couple of days up to a couple of weeks are required for curing, and then the surface is wet polished and dried before adding the next. The saya is placed in a warm and humid furo, kept as dust free as possible, to ensure the urushi will cure properly.