Making Washi Paper from Kozo Bark — Traditional Japanese Papermaking

Soak dried kozo bark strips in cold water overnight to rehydrate them. Place the swollen bark in a large pot, cover with water, add soda ash (approximately 15-20% of the dry bark weight), and boil gently for 2-3 hours until the fibres are soft and pull apart easily when pinched. The alkaline cooking dissolves the lignin, pectin, and hemicellulose that bind the fibres together, leaving pure cellulose. Rinse the cooked bark thoroughly in running water for 30-60 minutes, kneading and squeezing to flush out dissolved chemicals and dark-coloured extractives. Pick through the fibre by hand, removing any remaining bark fragments, knots, or discoloured spots.

Spread the rinsed fibre on a flat stone or hardwood board and beat it with a wooden bat or mallet. The goal is to separate and fibrillate the individual cellulose fibres without cutting them short. Long fibres produce strong paper — washi's characteristic toughness comes from kozo fibres that average 7-10mm in length, far longer than wood pulp fibres (1-3mm). Beat rhythmically, turning and folding the fibre mass periodically, for 20-40 minutes until it becomes a fluffy, cloud-like pulp with no visible bundles or clumps. Over-beating shortens the fibres and produces weaker, more opaque paper.

Fill the papermaking vat with clean water and disperse the beaten fibre pulp into it, stirring thoroughly. Add neri, a viscous mucilage made from crushed tororo-aoi (sunset hibiscus) root soaked in water. Neri is the critical ingredient that distinguishes Japanese nagashi-zuki papermaking from Western tame-zuki: it slows drainage through the screen, keeps fibres suspended evenly in the water, and allows the papermaker to build up layers with multiple scoops rather than forming the entire sheet in one action. Without neri, the fibres clump and drain too quickly for even sheet formation. Stir the vat contents before each sheet to re-suspend settled fibres.

Hold the sugeta (a hinged frame with a flexible bamboo screen called a su) and dip it into the vat at a slight angle. Scoop fibre slurry onto the screen, then rock the mould back and forth rhythmically, allowing the slurry to flow across the entire screen surface and then draining the excess off the far edge. This scooping-and-draining action is repeated 2-4 times per sheet, building up layers of criss-crossed fibres that interlock for strength. The number of scoops determines the sheet thickness. After the final scoop, tilt the mould to drain completely. Lift the su (screen) from the frame and lay the wet sheet onto a stack of previously formed sheets (called a post), placing each sheet directly on top of the last without any felt or couching cloth between them — the neri prevents them from bonding permanently.

After forming all sheets, press the entire stack (post) overnight under gradually increasing weight to squeeze out excess water. Start with light pressure and increase over several hours — sudden heavy pressure squeezes the wet sheets sideways, causing distortion. After pressing, peel individual sheets from the stack one at a time (they separate cleanly thanks to the neri) and brush each sheet onto a smooth drying board (traditionally made of ginkgo or cypress wood). Use a wide, soft brush to smooth the wet sheet onto the board surface, pressing out air bubbles. Dry the boards in the sun or in a warm, well-ventilated room. The dried sheets peel off the boards with a gentle tug. Finished washi is strong, flexible, slightly translucent, and has a soft, warm surface texture distinct from machine-made paper.