Japanese Washi and Bookbinding Structures

Washi — literally "Japanese paper" — is distinguished from Western handmade paper not only by its raw material but by its sheet-forming method. The difference in technique produces papers with properties that Western furnishes cannot easily replicate: extreme thinness combined with high tensile strength, long-fibre mats that resist tearing across their surface, and a surface texture that accepts calligraphic ink with a particular responsiveness.

In Canada, washi production is concentrated in a small number of studios, most notably in Montreal, where practitioners have developed adapted methods suited to local climate conditions and North American sources of kozo and abaca. This article covers the material and technical basis of washi production and its connection to traditional Japanese bookbinding.

Fibre Sources: Kozo, Mitsumata, and Gampi

Three plant species dominate traditional washi production:

• Kozo (Broussonetia kazinoki × B. papyrifera): The most widely used washi fibre. Kozo produces long, strong fibres with relatively coarse texture. It is the fibre of choice for document papers, book repair tissues, and papers that must withstand handling stress. North American growers, including a small number of Canadian producers, now cultivate kozo varieties suited to temperate climates.
• Mitsumata (Edgeworthia chrysantha): Softer, shorter fibres than kozo. Mitsumata papers have a slightly glossy surface and absorb ink evenly, which made them the preferred base for Japanese government documents and currency paper for much of the twentieth century.
• Gampi (Wikstroemia sikokiana): The rarest and most difficult to cultivate of the three. Gampi fibres are very fine and resist biological degradation better than kozo or mitsumata, giving gampi papers exceptional longevity. It is not currently cultivated outside Japan at commercial scale.

In Canadian studios, abaca (Manila hemp) is frequently blended with imported kozo to adjust strength and formation characteristics. Pure kozo from Japanese suppliers is available through specialised paper arts distributors, though costs are considerably higher than for cotton-based Western furnishes.

Fibre Preparation: Cooking and Beating

Raw kozo bark is harvested in winter when fibre quality is highest. The outer dark bark (kuro-kawa) is scraped away to expose the white inner bast fibre (shiro-kawa). The cleaned fibre is cooked in a lye solution — traditionally wood ash lye, now more commonly soda ash — to break down the lignin and hemicellulose that bind the fibre bundles.

After cooking, the fibres are washed and then beaten by hand with a wooden mallet on a flat stone — the traditional method still used in high-quality washi production — or by light mechanical beating. Washi production uses considerably less beating than Western papermaking: over-beating destroys the long fibre length that gives washi its strength.

Careful manual sorting (chiritori) removes any remaining dark particles and bark fragments from the wet fibre before it enters the vat. In premium washi production, chiritori is done in natural light, with workers picking out individual impurities by hand. This step directly determines the visual cleanliness of the finished sheet.

Neri: The Suspension Agent

The key technical difference between Japanese and Western sheet-forming is the addition of neri — a natural mucilaginous suspension agent — to the papermaking vat. Traditional neri is extracted from the roots of tororo-aoi (Abelmoschus manihot), a member of the mallow family. The mucilage slows the drainage of water through the su (the flexible bamboo screen), giving the papermaker time to build up multiple thin layers of fibre with the swinging nagashizuki motion.

Without neri, the furnish drains too quickly through the fine su screen for the nagashizuki technique to work. The mucilage also helps keep fibres uniformly dispersed in the vat — preventing clumping that would produce uneven formation. Neri breaks down naturally during drying and leaves no residue in the finished sheet.

In Canada and other non-Japanese settings, synthetic polyacrylamide (PEO — polyethylene oxide) is sometimes substituted for tororo-aoi neri when the natural material is unavailable. Practitioners report that PEO works acceptably for most applications but does not replicate the precise drainage control of natural tororo-aoi neri in large-format sheets.

The Nagashizuki Technique

Washi sheet formation uses a flexible bamboo su laid on a rigid keta (wooden frame) rather than the rigid wire mould of Western practice. The papermaker dips the su-and-keta into the vat, lifts it with a charge of furnish, and then moves it in a repeated swinging motion — front-to-back and side-to-side — repeatedly sending the furnish across the surface and tipping excess back into the vat. This is repeated through multiple charges, building up a sheet from many thin layers.

The repeated layering and the slow drainage controlled by neri produce a sheet in which the fibres are oriented more randomly than in Western paper — with a slight predominance in the direction of the primary swing. The result is a sheet with very high tear resistance relative to its weight: a 12 gsm Japanese tissue can have greater tensile strength than a 60 gsm Western machine-made paper of comparable fibre composition.

Drying Washi

Couched washi sheets — transferred directly from the su to a smooth board or stacked with thin plastic sheets between them — are brush-dried against wooden boards in the traditional Japanese method. Each wet sheet is carefully smoothed onto a flat board using a wide, soft brush, then left to air-dry or dried over a heated board. The tension created as the sheet contracts during drying produces a flat, taut surface.

This drying method is climate-sensitive. In humid Canadian summers, drying times increase significantly; in dry winter interiors, sheets can over-dry and crack at the edges if not monitored. Some Canadian studios use humidity-controlled drying rooms to standardise the process year-round.

Japanese Bookbinding Structures

Washi's physical properties — flexibility, strength, and consistent thickness — made it the foundation of traditional Japanese book formats. The main structures are:

• Yamato-toji (stab binding): Four or five holes punched through the folded text block, with thread sewn in a pattern visible on the spine edge. The simplest Japanese binding, used for notebooks and document collections. The thread pattern varies by tradition — kikko (tortoiseshell), hemp leaf, and tortoiseshell-and-hemp patterns are among the most common.
• Fukuro-toji (pocket/pouch binding): Pages folded at the spine edge, with the open double-leaf edge stitched. The folded edge faces outward — an arrangement that protects the text from the sewing thread and distributes stress across the fold rather than through sewing holes in the paper.
• Orihon (accordion fold): A continuous sheet folded back and forth, with hard covers attached at each end. Used for sutras, illustrated scrolls, and reference texts that benefit from continuous unfolding. The fold structure allows the book to be opened at any point without stress on individual pages.
• Danso (twill stitch): A more elaborate stab binding in which the thread passes through the text block at angles, creating a diagonal pattern along the spine. More secure than basic yamato-toji for heavy use.

Canadian bookbinding instructors — particularly through the Canadian Bookbinders and Book Artists Guild (CBBAG) — teach Japanese binding structures as part of the core curriculum. Yamato-toji and fukuro-toji are commonly used by Canadian book artists working with their own handmade washi or with imported Japanese papers.

Washi in Conservation and Repair

Beyond its use in original papermaking, washi — particularly thin kozo tissues — is the material of choice for paper conservation repair work worldwide. A 2–4 gsm kozo tissue applied with dilute wheat starch paste can reinforce tears in fragile Western papers without adding perceptible bulk or changing the visual character of the repaired sheet. Canadian conservators working at institutions such as Library and Archives Canada and provincial archives routinely use Japanese tissues in this way.