Reported practice · r/Kintsugi

Diagnosing and preventing uneven marufun polish-through in a kintsugi repair

A practitioner completed a kintsugi repair finished with marufun (spherical metal powder) and is unsure whether the uneven, partially exposed undercoat is a technique failure or an intentional decorative style. The thread works through what went wrong in the application and finishing sequence and offers corrective guidance for future pieces.

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 produce a delayed urushiol-type dermatitis, and sensitisation is cumulative: once sensitised, even trace contact triggers a reaction. Wear nitrile or neoprene gloves and avoid any skin contact with wet or partially cured lacquer.

Turpentine, mentioned as a thinning agent for the urushi adhesion layer, is a volatile organic solvent. Work in a ventilated area and avoid prolonged inhalation of vapours.

What the thread establishes

The answer.

The uneven result is a technique issue, not a style. The core problems identified are an insufficiently smooth substrate, an uneven or improperly cured urushi adhesion layer, and overly aggressive or inconsistent polishing. Corrective guidance centres on preparing a perfectly flat ground, applying the urushi layer as thin and even as possible (thinning with turpentine if it will not self-level), sprinkling with a funzutsu of the correct mesh, allowing both the under- and over-powder urushi to cure fully, and then sanding and polishing in very small increments while examining the surface after every couple of strokes. For silver work, one commenter recommends blending roiro with kijomi in a ratio between 1:5 and 1:1 to neutralise the brown cast while retaining hardness. For wide areas, a coarse powder (#7–#9) is applied first, excess tapped away, then a finer grade (#2–#4) laid over it to build an even layer.

—

What goes wrongThe marufun layer polished unevenly: in some areas the abrasive removed the powder entirely and exposed the black urushi undercoat, while in other areas insufficient abrasion left a dull, thick powder surface. The OP recognised this as soon as sanding began and noted a narrow band of visible undercoat around the perimeter of the repair. One commenter suggests the cause may be over-abrasion or the powder sinking into an under-cured urushi layer.

What recovers itNo in-situ repair of the finished piece is described. One commenter notes the piece looks acceptable from the top and that few will inspect the interior of the lid. The OP expresses willingness to accept the result for a personal piece. The practical recovery is applying the corrected procedure to the next project, which the OP reports is already going better.

Prepare a perfectly smooth substrate

Marufun is unforgiving of any unevenness beneath it. Any irregularity in the ground will cause the powder to be polished through in some spots and left too thick in others. Flatten and level the surface before beginning.

the comment this came from ↗

Apply a thin, even urushi adhesion layer

Spread the urushi that will hold the powder as thinly and evenly as possible. If the lacquer is too thick to self-level, thin it slightly with turpentine. Ensure no dust or debris is trapped in the layer.

the comment this came from ↗

Sprinkle powder with a funzutsu

Use a funzutsu fitted with a mesh appropriate to the powder grade. For wide or large areas, first sprinkle a coarse powder (#7–#9), tap or dust away the excess, then immediately sprinkle a finer grade (#2–#4) over it. The coarse layer helps keep the overall thickness even; the fine layer provides coverage.

the comment this came from ↗

Allow full cure before any abrasion

Both the urushi beneath the powder and the urushi above it must be fully cured. The lacquer needs to be as hard as possible so it holds the powder during sanding and polishing.

the comment this came from ↗

Alternate polish grades with a rubbed-in lacquer layer

Between each grade of polishing stone, rub in a layer of kijomi (or, for silver, a blend of roiro and kijomi in a ratio of roughly 1:5 to 1:1) to build the final shine. The roiro component cancels the brown cast of the kijomi while contributing hardness.

the comment this came from ↗the comment this came from ↗

··Reported

What was reported

Marufun is extremely sensitive to substrate smoothness; any unevenness underneath will manifest as uneven polish-through. ↗
The urushi adhesion layer can be thinned with turpentine if it is too viscous to self-level. ↗
A funzutsu with the correct mesh size is important for even powder distribution. ↗
Both the urushi under and over the powder must be fully cured before sanding or polishing begins. ↗
For silver marufun work, a blend of roiro and kijomi in a ratio between 1:5 and 1:1 neutralises the brown cast of the kijomi while providing hardness. ↗
A darkening of the silver powder is an inevitable characteristic of marufun; even, well-covered application means the shine recovers sufficiently after polishing that the darkening is barely noticeable. ↗
The OP's piece was finished over two cured applications of black urushi as the undercoat. ↗
The OP found that 2000-grit sanding followed by charcoal polishing gave better results than grit alone, and that far less pressure than expected was required. ↗
The OP acknowledges that they likely sanded too much silver away and did not apply the marufun powder correctly, but accepts the result for a personal piece. ↗
One commenter who has not yet attempted marufun describes it as having too much room for error at their current skill level. ↗
The OP was considering a funzutsu in the 250–350 micron range for #7 powder, though the exact correct size was not confirmed in the thread. ↗

≠Disputed

Optimal urushi thickness and cure state when sprinkling marufun

The thread does not settle this

Apply a slightly thicker urushi layer, allow a partial cure, then sprinkle the powder. ↗
Apply a super-thin urushi layer and sprinkle while it is still completely wet. This is easier in practice but wastes more metal powder if the layer is too thick, and the thin layer is harder to get perfectly smooth because self-leveling is reduced. ↗

Limits of this source

What the thread does not answer.

The exact funzutsu mesh size appropriate for #7 marufun was requested but not confirmed; the commenter who was asked said they would check and get back.
The two schools of urushi thickness and cure state at the moment of sprinkling (thicker + partial cure vs. ultra-thin + wet) are presented without a definitive resolution; the OP chose the thicker method for this piece and plans to try the thinner approach next.
The OP's original question about whether the result constitutes a recognised 'moon crater' style is never answered by any commenter; the thread treats it as a technique issue rather than a style.

Read the documented methods →