01
Prepare hemp fiber from cloth
Cut hemp cloth into segments roughly 1–3 mm long on a diagonal to the weave, then rub the pieces between the fingers to separate the threads into individual fibres suitable for kokuso-urushi.
Reported practice · r/Kintsugi
Sourcing and preparing kokuso-urushi components domestically
A practitioner in the US needs to fill large chips (roughly 50 mm long, 5 mm wide and deep) in a porcelain cup using kokuso-urushi and is asking where to obtain hemp fiber, fine sawdust, and nori-urushi, or whether those components can be made from locally available materials. A secondary question concerns whether a diluted ki-urushi seal coat is appropriate on a non-porous porcelain surface before the repair.
This page is written from one discussion thread. It records what practitioners reported and what they linked it to — not documented workshop practice. Every claim below links to the comment it rests on, so you can read it in context.
Raw urushi (ki-urushi) contains urushiol, a potent skin sensitiser. Contact can trigger a delayed allergic dermatitis that may not appear for 24–72 hours and can spread with subsequent exposure. Handle all urushi mixes with gloves and avoid skin contact throughout the mixing and application steps described here.
The post mentions white gas (naphtha) as a kerosene substitute for diluting ki-urushi. Naphtha is a highly flammable solvent; use only in a well-ventilated area away from ignition sources.
What the thread establishes
The answer.
The thread establishes that all three kokuso-urushi components can be prepared locally without importing from Japan. Hemp fiber is obtained by cutting hemp cloth into small diagonal segments and unravelling the threads by hand; untreated natural-fibre rope is an alternative. Fine sawdust is produced by drilling or scraping a white temperate hardwood such as birch, taking care to avoid tropical species whose extractive oils can inhibit urushi curing. Nori-urushi is a self-mixed adhesive: a rice-based paste (cooked sticky rice, or glutinous-rice flour/starch with boiling water) combined with raw urushi, in a ratio around 1 : 1. For the porcelain surface specifically, the thread advises that a diluted-urushi seal coat is unnecessary because porcelain is non-porous, and recommends nikawa-urushi (warm hide glue or unflavoured gelatin plus ki-urushi) as the bonding agent for the repair instead.
02
Produce fine hardwood dust
Drill a birch or other white temperate hardwood dowel and file the shavings over a sheet of paper to a fine powder, or alternatively shave a piece of hardwood with a scraper. Avoid tropical hardwoods, whose natural oils can prevent urushi from curing.
03
Mix nori-urushi adhesive
Prepare a rice-based paste by cooking short- or medium-grain sticky rice (or glutinous-rice flour/starch) with hot water until smooth, then combine it with raw urushi in approximately equal parts. The process is analogous to making mugi-urushi.
04
Bond porcelain repair with nikawa-urushi
Because porcelain is non-porous, skip the diluted-urushi seal coat. Instead, prepare nikawa-urushi by mixing warm hide glue (or unflavoured gelatin as a substitute) with ki-urushi, and use it to adhere the kokuso-urushi fill to the chip.
··Reported
What was reported
- Hemp fibre for kokuso-urushi can be produced by cutting hemp cloth into small diagonal segments and unravelling the threads by hand, eliminating the need to import pre-cut fibre. ↗
- Fine sawdust for kokuso-urushi should come from a white temperate hardwood (e.g. birch); tropical hardwoods contain extractive oils that can inhibit urushi curing. ↗
- Nori-urushi is a self-mixed adhesive combining a rice-based paste with raw urushi, and its preparation is analogous to mugi-urushi. ↗↗
- Porcelain is non-porous and does not require a diluted-urushi sealing coat before a kokuso-urushi repair. ↗
- Nikawa-urushi, made from warm hide glue (or unflavoured gelatin) plus ki-urushi, is recommended as the bonding agent for porcelain repair when a glass-compatible urushi is unavailable. ↗
- Untreated natural-fibre rope can be chopped and shredded as an alternative source of fibre for kokuso-urushi. ↗
- Ordering wood dust or hemp fibre specifically for urushi work from a Japanese supplier is not recommended unless the practitioner is already placing a broader order with that supplier. ↗
≠Disputed
Starting material for the rice-based adhesive in nori-urushi
Limits of this source
What the thread does not answer.
- Whether the poster's existing 50 % ki-urushi / white-gas dilution already applied to the porcelain surface is harmful or simply redundant, or whether it will interfere with the subsequent nikawa-urushi bond.
- The long-term durability and flexibility of unflavoured gelatin as a hide-glue substitute in nikawa-urushi, particularly on a functional cup that will see thermal cycling.
- Whether a chip of roughly 50 mm × 5 mm is within the practical range for kokuso-urushi fill or whether a different structural repair (e.g. a patch or inlay) would be more appropriate.