Reported practice · r/Urushi

Embedding coarse particles in urushi for a durable textured surface

How can a practitioner embed relatively large particles (coarse sand, seeds) into a lacquer ground so that the texture remains visible and the surface is durable enough for functional ware, while the particles stay firmly in place?

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.

Safety

Raw ki-urushi is a potent skin sensitiser; the reaction is delayed (often 24–72 hours) and can be severe. The thread involves repeated direct handling of raw lacquer, thinning it with naphtha, and brushing it onto particles. Gloves, long sleeves, and avoidance of skin contact are essential. Naphtha (white gas) is a flammable solvent and should be handled in a well-ventilated area away from ignition sources.

What the thread establishes

The answer.

The thread reports that pressing coarse particles into a layer of sabi and then sealing them with additional lacquer coats is workable, though the method of sealing matters greatly. Raw ki-urushi brushed directly over fine sand (0.2–0.6 mm) tends to dislodge the particles and tear the bond; thinning the lacquer to roughly 25 % with naphtha (white gas) before brushing allows it to flow into the gaps without disturbing the sand. For larger particles such as quinoa seeds, a thick application of bengara (iron-oxide) lacquer left to flow by gravity into the interstices overnight in the curing room produced a smooth, cohesive surface with the seed texture still visible. The traditional route for textured surfaces, as noted by a commenter, is to sprinkle the particles onto a wet coat of urushi rather than onto sabi, build up additional coats, cure, sand, and finish with further lacquer layers. A related traditional technique, nanako-nuri, embeds seeds and then removes them to leave a pitted texture, requiring extra curing time after removal because the lacquer beneath the seeds may not yet be fully set.

—

What goes wrongBrushing raw ki-urushi directly over fine sand (0.2–0.6 mm) causes the sand to lift and the poorly bonded layer to tear under the brush. Applying highly diluted ki-urushi over quinoa seeds leaves a weak, irregular surface in the gaps between seeds. Brushing raw ki over quinoa seeds deposits too much lacquer on top of the seeds, obscuring their colour and texture.

What recovers itFor fine sand, thin the ki-urushi to approximately 25 % with naphtha before application so it flows into the interstices without disturbing the particles. For larger seeds, apply a thick coat of bengara lacquer and allow gravity to draw it into the gaps over an overnight period in the curing room; the viscous pigment settles into the interstices while the seed surfaces remain visible. Alternatively, brush a small amount of naphtha over the freshly applied ki-urushi to wipe excess off the seed tops, though this deposits less lacquer in the gaps and may not build a sufficiently hard surface.

Apply the Tosa Kodai Nuri textured-ground sequence

Brush a coat of urushi onto the surface. Using a sieve, sprinkle the desired powder (e.g. crushed walnut shell) evenly over the wet lacquer. Apply a second coat of lacquer to fix the powder. Sprinkle a layer of red pigment over the top. Brush a coat of black lacquer over the whole surface. Allow the assembly to cure fully. Lightly sand the surface to level it. Apply further coats of urushi as the finish requires.

the comment this came from ↗

··Reported

What was reported

Pressing coarse particles (sand, quinoa seeds) into a layer of sabi and curing for a couple of days produces a firm bond that resists dislodgement under moderate rubbing. ↗
Brushing raw ki-urushi directly over fine sand in the 0.2–0.6 mm range tends to lift the sand and tear the bond; the sand also clogs the brush. ↗
Thinning ki-urushi to roughly 25 % with naphtha (white gas) allows it to be brushed over fine sand without destroying the particle layer. ↗
A thick coat of bengara lacquer applied over embedded quinoa seeds flows by gravity into the interstices over an overnight period in the curing room, producing a cohesive surface with the seed texture still visible. ↗
The traditional technique for textured surfaces most commonly involves sprinkling kanshitsu-fun, tonoko, jinoko, charcoal powder, or crushed shell onto a wet urushi coat, building up additional coats, curing, sanding, and finishing with further lacquer layers. ↗
The walnut-shell textured technique is associated with a specific regional tradition called Tosa Kodai Nuri and appears to be a small, possibly declining, niche practice rather than a widely documented method. ↗↗
Nanako-nuri is the traditional technique of embedding seeds (classically canola seeds) in lacquer and then removing them to leave a pitted, grippy texture. ↗
In nanako-nuri, after the seeds are removed, the lacquer beneath them may not be fully cured even after several weeks in the curing room, so additional curing time is required before further work. ↗
The OP's planned application is a textured rim on the exterior of a rice bowl, with seeds sandwiched between a sabi layer and a bengara-urushi layer, worked in sections to allow gravity to draw the viscous lacquer into the gaps before rotating to the next section. ↗
Brushing naphtha over freshly applied ki-urushi on quinoa seeds removes excess lacquer from the seed surfaces but deposits insufficient lacquer in the interstices to build a hard, smooth final surface. ↗

≠Disputed

Whether sabi or plain urushi is the appropriate base layer for embedding coarse particles

The thread does not settle this

The traditional method is to sprinkle particles onto a wet coat of urushi, not onto sabi; sabi is not the conventional adhesive for this purpose. ↗↗
Using sabi as the base is deliberate and practical: it allows large particles of varying size to be pressed down to a relatively uniform plane, with larger particles sinking deeper, producing a flatter top surface than wet urushi would. ↗↗

≠Disputed

Whether the sabi bond is strong enough to hold the particles

The thread does not settle this

Sabi is probably not the best adhesive for this application; a tackier, higher-viscosity medium such as nori-urushi, mugi-urushi, or shibo-urushi would be preferable. ↗
In practice the particles were firmly embedded in the sabi; vigorous rubbing with cardboard did not dislodge them, so the bond is adequate for the intended use. ↗

Limits of this source

What the thread does not answer.

Whether the OP's method of sandwiching quinoa seeds between a sabi layer and a bengara-urushi layer will produce a surface durable enough for regular washing and use on a functional rice bowl.
Whether the weak, irregular lacquer surface between quinoa seeds produced by highly diluted ki-urushi can be resolved with additional coats or a different sealing method.
Whether the 0.2–0.6 mm sand size range can be made to work reliably, or whether it sits in an unworkable gap between makiji-scale particles and the larger seeds that do bond well.
The long-term stability of the textured surface under repeated thermal and mechanical stress (e.g., hot rice, washing, handling).
Whether the Tosa Kodai Nuri walnut-shell technique has any published process documentation beyond the single third-party blog post referenced in the thread.

Read the documented methods →