漆Urushi Archive

Reported practice · r/Urushi

Diagnosing and correcting chijimi (puckering) on a coloured urushi coat

A practitioner applying a glossy red urushi finish over a raw-urushi ground reports surface puckering after curing at 70–85 % humidity for 5–7 days per coat. A secondary question asks whether urushi can be applied to bone as a substrate.

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 urushi (ki-urushi) is a potent skin sensitiser; contact can trigger a delayed urushiol-type dermatitis that may appear 12–72 hours after exposure. The thread involves repeated handling of raw and refined urushi, so barrier protection and prompt washing of any splashed material are important.

What the thread establishes

The answer.

The puckering is identified as chijimi, caused by a coat that is too thick for the curing conditions or by humidity and temperature that are too high for the thickness being applied. The corrective approach is to reduce the effective coat thickness—by loading less lacquer onto the brush, brushing it out more evenly, or diluting the lacquer slightly—and to lower the curing humidity, particularly in the first hours. One commenter recommends beginning the cure at roughly 70 % relative humidity (or a touch below) and raising it to 80 % only after about half a day, while keeping the ambient temperature near 20 °C to slow the cure. A second commenter adds that premixed coloured urushi tends to be thicker than raw or un-pigmented refined lacquer, so the same 'thin' application may in fact be too heavy; thinning with a solvent such as petroleum essence or turpentine is suggested, with the caveat that the thinned material runs more and can pool in corners. If the lacquer is already fluid, the opposite adjustment—letting it stand briefly so it thickens before application—may reduce pooling. For the bone question, one commenter has not tried it but reasons that a smooth finish would require a priming ground analogous to that used on wood or ebonite, while a finish that lets the bone texture show through would call for a very thin seal coat of raw urushi before the upper layers; the commenter considers bone a plausible substrate but offers no confirmed result.

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What goes wrongSurface puckering (chijimi) appears on the final red coat. It is recognised as a pattern of fine wrinkles across the surface, often concentrated in inside corners where the lacquer has pooled while the piece rested. The underlying cause is a mismatch between coat thickness and the curing environment: the layer shrinks as it cures and the skin that forms on top wrinkles rather than staying flat.

What recovers itReduce the coat thickness by loading less lacquer, brushing it out more evenly, or diluting the lacquer slightly before application. Lower the curing humidity, especially during the first hours of the cure, and keep the temperature modest so the cure proceeds slowly. If the lacquer pools in corners, the piece may be flipped partway through the cure so the pooled material redistributes. For premixed coloured urushi that feels thick, thin it with a small amount of petroleum essence or turpentine; for already-fluid lacquer, let it stand briefly so it loses some runniness before applying. The thread notes that resolving chijimi is largely a matter of repeated small adjustments rather than a single fix.

01

Cure a coloured or thick coat in two humidity stages

Begin the cure at approximately 70 % relative humidity or slightly below. After roughly half a day, raise the humidity to 80 % for the remainder of the cure. Keep the ambient temperature near 20 °C so the cure proceeds slowly enough to avoid the shrink-wrinkle that produces chijimi.

the comment this came from ↗
02

Adjust coat thickness to match the curing environment

If the lacquer is thick (as premixed coloured urushi often is), thin it slightly with petroleum essence or turpentine and apply a genuinely thin, even layer, being careful that the thinned material does not run into corners. If the lacquer is already fluid, let it stand briefly so it loses some runniness before applying, to reduce pooling in recesses.

the comment this came from ↗
··Reported

What was reported

  • Puckering (chijimi) is produced by one or both of two conditions: the urushi layer is too thick, or the curing humidity and temperature are too high for that thickness. ↗
  • Premixed coloured red urushi tends to be noticeably thicker and harder to apply evenly than raw or un-pigmented refined lacquer, so a coat that feels thin may still be too heavy. ↗↗
  • Puckering is often concentrated in inside corners because the lacquer pools there while the piece rests; flipping the piece partway through the cure can redistribute the pooled material. ↗
  • Thinning urushi with petroleum essence or turpentine makes it more runny and increases the risk of pooling, so the application must be kept very thin. ↗
  • If the urushi is already fluid, allowing it to stand briefly before application so it thickens slightly can reduce pooling in recesses. ↗
  • Resolving chijimi is described as a process of repeated small adjustments rather than a single corrective action. ↗
  • For a smooth urushi finish on bone, a priming ground analogous to that used on wood or ebonite is needed; for a finish that lets the bone texture show, a very thin seal coat of raw urushi before the upper layers is suggested. No commenter reports a confirmed successful result on bone. ↗
  • The poster's working conditions: 2–3 thin coats of raw urushi as a ground, cured 5–7 days per coat at 70–85 % humidity, with the puckering appearing on the subsequent glossy red coat. ↗

Limits of this source

What the thread does not answer.

  • Whether urushi adheres durably to bone and what ground preparation is actually required is unconfirmed; the only guidance offered is speculative and based on analogy to wood and ebonite.
  • The thread does not establish whether the chijimi on the red coat was caused primarily by coat thickness, by the 70–85 % humidity range, or by the specific viscosity of the premixed red lacquer; the poster has not yet reported a successful correction.
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