漆Urushi Archive

Reported practice · r/Kintsugi

Preventing urushi wicking into crackle glaze during kintsugi repair

A wood-fired ceramic bowl with heavy ash-glass craquelure is broken into four pieces plus a hairline crack. The practitioner needs to join and fill the pieces with urushi but fears the lacquer will wick along the crackle lines and permanently darken them, especially because the crazing reaches the fragment edges where masking tape cannot seal the sides.

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

Ki-urushi (raw lacquer) is a potent skin sensitiser. Contact can cause a delayed urushiol-type dermatitis that may appear 12–72 hours after exposure and can become progressively more severe with repeated contact. Gloves, long sleeves, and avoidance of skin contact are essential when handling the sap, especially in the thin-edge-sealing and crack-filling steps described here.

What the thread establishes

The answer.

The thread converges on a two-part priming strategy. First, the raw edges of each fragment are sealed with an extremely thin coat of ki-urushi and allowed to cure; this both limits later absorption and improves adhesion when the pieces are assembled. Second, the glazed faces are primed with prepared egg-white glair, applied thin enough to be visible pulling into the craquelure, wiped of excess, and left to dry for a day or two before any urushi is applied to the surface. Masking tape is retained as a supplementary barrier but is acknowledged as insufficient on its own. For the hairline crack the practitioner must apply just enough urushi (possibly ethanol-diluted to improve capillary flow) to fill the fissure while accepting that some wicking into the surrounding glaze is unavoidable.

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What goes wrongUrushi wicks along the craquelure lines and darkens them. Masking tape placed over the surface does not prevent this because the crackle channels run to the very edges of the fragments, so lacquer enters from the sides regardless of the tape on top. The problem is recognised by the characteristic darkening of the fine crackle network after urushi contact.

What recovers itThe thread does not describe a method for reversing urushi staining once it has wicked into the glaze. The emphasis is entirely on prevention through the glair priming and edge-sealing steps before any decorative or structural urushi is applied.

01

Seal fragment edges with ki-urushi

Dab an extremely thin, even layer of ki-urushi along the broken edges of each fragment. Allow it to cure fully. This limits later absorption and promotes adhesion when the pieces are joined.

the comment this came from ↗
02

Prepare egg-white glair

Process the egg whites using a method that increases their fluidity (the commenter references a glair-for-painting preparation), so the liquid can seep into the fine craquelure channels.

the comment this came from ↗
03

Prime the glazed surface with glair

Apply the glair thinly over the glazed faces. It should be thin enough that you can watch it being drawn into the crackle lines. Wipe off the excess, then let it dry for a day or two before proceeding.

the comment this came from ↗
04

Apply masking tape as a supplementary barrier

Even after glair priming, place masking tape over areas where urushi will be worked, to reduce the chance of any residual staining. The tape is a secondary safeguard, not the primary one.

the comment this came from ↗
··Reported

What was reported

  • Craquelure on wood-fired pottery will wick urushi into the crack lines and darken them. ↗
  • Masking tape placed over the surface is insufficient when the craquelure reaches the fragment edges, because urushi enters from the sides. ↗
  • Egg-white glair, prepared to be sufficiently fluid, can be used to prime and seal craquelure channels before urushi application. ↗
  • Sealing the broken edges with a thin coat of ki-urushi before assembly both limits absorption and improves later adhesion. ↗
  • The susceptibility of a given glaze to urushi wicking depends on firing temperature, sodium content, and the type and quantity of ash present. ↗
  • Masking fluid can be used as an alternative barrier but may itself stain certain clay bodies. ↗
  • For a hairline crack, ethanol dilution of ki-urushi can improve capillary flow into the fissure. ↗
  • Practising on unglazed terracotta pots is advisable before working on a finished glazed piece. ↗
≠Disputed

Whether to use straight ki-urushi or ethanol-diluted ki-urushi for the hairline crack

The thread does not settle this
  • Some tutorials recommend applying straight ki-urushi to the hairline crack. ↗
  • Other tutorials recommend diluting the ki-urushi with ethanol so it wicks more readily into the narrow fissure. ↗

Limits of this source

What the thread does not answer.

  • Whether straight ki-urushi or ethanol-diluted ki-urushi gives a stronger, more durable fill in a hairline crack on a glazed surface; the thread presents both options without resolving which is preferable.
  • What, if anything, can be done to remove or mask urushi staining that has already wicked into the craquelure after the fact.
  • The specific firing history of the bowl (temperature, ash composition, sodium content) remains unknown, so the exact degree of wicking susceptibility cannot be predicted.
Read the documented methods →