漆Urushi Archive

Reported practice · r/Kintsugi

Timing gold-powder application over a kintsugi repair and diagnosing chijimi

A practitioner applying gold powder over a red-lacquer coat in a kintsugi repair finds the powder sinking into the still-wet lacquer and losing its shine, and also observes a wrinkled surface after a red coat. The thread addresses how to judge when the lacquer is ready to receive powder, what causes the wrinkling, and how to recover from both problems.

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; contact can trigger a delayed urushiol-type dermatitis that may appear hours to days after exposure. Practitioners handling undiluted or turpentine-diluted ki-urushi should wear nitrile or neoprene gloves and avoid skin contact, particularly on the hands and forearms.

Because the finished repair is on a vessel that will contact food and the mouth, any metal powder used should be confirmed food-safe (gold and silver are; some cheaper substitutes are not).

What the thread establishes

The answer.

Readiness for gold powder is judged not by a fixed clock time but by the hiki test: blow gently on the cured surface as one would fog a window. A rainbow sheen (aohiki) indicates the lacquer is half-cured and ready; a plain white sheen (shirohiki) means it is fully cured and the powder will not adhere. Before committing the whole surface, dust a small test area and wait two to five minutes; if the powder remains on the surface the rest can be dusted, but if it has sunk the piece should return to the muro for five to ten minutes and the test repeated. The muro should hold roughly 25 °C and 70–80 % relative humidity. Chijimi (wrinkling) results from the muro being too hot, too humid, or both, or from the lacquer coat being applied too thickly so the top skin sets before the body cures. Recovery in both cases is to sand the affected layer flat and reapply a fresh, thin coat before attempting the powder again.

—

What goes wrongGold powder is absorbed into the lacquer coat and loses its reflective shine, or the cured surface develops wrinkles (chijimi). The sunken-powder problem is recognised by the powder disappearing into the surface and a dull, non-metallic appearance after sanding. Chijimi is recognised as a wrinkled or rippled texture on the cured coat.

What recovers itFor sunken or dull gold: sand the affected area, apply a fresh thin coat of the appropriate lacquer (kuro-urushi or shu-urushi), cure in the muro, and reapply powder once the hiki test confirms readiness. For chijimi: sand the wrinkled layer flat and repaint with a thinner coat under corrected muro conditions.

01

Level the sabi flush with the surrounding surface

Before any further coats, abrade the sabi putty so it sits level with the adjacent glaze or body. A raised sabi will telegraph through subsequent coats and complicate the final polish.

the comment this came from ↗
02

Saturate the sabi with diluted ki-urushi

Mix ki-urushi with turpentine and brush it into the sabi until saturated, then absorb the excess. Cure the piece overnight in the muro. Take care at the edges of a porous or stained piece to avoid bleeding.

the comment this came from ↗
03

Apply and cure two coats of kuro-urushi

Brush on the first coat of kuro-urushi and cure overnight in the muro. Polish the surface flat, then apply a second coat and cure overnight again.

the comment this came from ↗
05

Test-dust a small area before committing the full surface

Dust a small portion of the repair with gold powder and wait two to five minutes. If the powder remains on the surface, dust the rest. If it has sunk, return the piece to the muro for five to ten minutes and repeat the test.

the comment this came from ↗
06

Fill the chip with sabi-urushi in measured passes

Apply sabi-urushi into the loss in layers of up to 2 mm thickness, curing between applications and polishing between coats until the fill is level.

the comment this came from ↗
07

Build up bengara-urushi coats and finish with a thin red coat

Apply multiple coats of bengara-urushi (iron-oxide red), polishing between each. Finish with a very thin coat of red lacquer and cure briefly until the surface is sticky but firmer, then apply keshifun. Allow approximately four months for full cure before the piece is put to use.

the comment this came from ↗
··Reported

What was reported

  • Blowing on a curing lacquer surface produces a rainbow sheen (aohiki) when the coat is half-cured and ready for powder, or a plain white sheen (shirohiki) when it is fully cured and too late for powder to adhere. ↗
  • A muro set to roughly 25 °C and 70–80 % relative humidity is the target range for controlled curing; deviating toward higher heat or humidity risks chijimi. ↗
  • Chijimi (wrinkling) can also be caused by applying the lacquer coat too thickly, so that the top skin sets before the underlying body cures. ↗
  • Particle size of the metal powder affects how readily it sits on the surface versus sinking into the lacquer; coarser powders such as bronze are more forgiving than fine gold dust. ↗↗
  • Silver powder is a practical substitute for gold during practice because it is food-safe, sold in the same particle sizes, and significantly cheaper. ↗
  • Crazing in the ceramic glaze can wick lacquer into the crack network, preventing gold powder from adhering in those channels and leaving dark lines; the crazing channels can be plugged with white glue or boiled milk before the final lacquer coat. ↗
  • The level of the sabi relative to the surrounding surface is a matter of aesthetic preference rather than a fixed rule; some practitioners prefer it flush, others slightly proud. ↗
  • Many variables influence the curing behaviour of a lacquer coat: ambient weather, muro humidity and temperature, the quality and age of the urushi, coat thickness, and whether solvent has been added. ↗
  • Ki-urushi can be diluted with turpentine to improve penetration into sabi before the structural coats are applied. ↗
  • The practitioner deliberately allows urushi to wick into glaze crazing beyond the repair line to create a suture-like visual effect, while avoiding it on the rest of the piece where it looks dirty. ↗
≠Disputed

How to determine when the red-lacquer coat is ready for gold powder

The thread does not settle this
  • A fixed curing window of fifteen to thirty minutes in the muro is sufficient before sprinkling gold. ↗
  • Fixed times are unreliable because they depend on muro conditions; the correct indicator is the hiki test (aohiki vs shirohiki) combined with a small test-dusting of two to five minutes. ↗
  • The coat should be cured only until it is still sticky but firmer, with no specific time given; full cure before use takes roughly four months. ↗

Limits of this source

What the thread does not answer.

  • The thread does not resolve whether the OP's original failure was due to coat thickness, muro conditions, or both; the practitioner plans to retry but no confirmed outcome is reported.
  • The interaction between boiled-milk or white-glue plugs in crazing channels and subsequent lacquer adhesion is suggested but not demonstrated in the thread.
  • The exact particle-size threshold at which gold powder begins to sink rather than sit on the surface is not quantified; only a qualitative observation that coarser bronze was more forgiving.
  • The thread does not address how to polish the final gold surface to a mirror finish, which was the OP's original title question.
Read the documented methods →