Kintsugi 101

– Kintsugi

This page is a work in progress as I document my research on traditional kintsugi with urushi lacquer. No cashew, no turpentine, no epoxy, and no shortcuts. This is the first article in the series and it’s the best place to start.

First published December 2020

Kintsugi Index

Why traditional?

My main concern with epoxy based adhesives is the fact that they are made of BPA or BPA alternatives, which might not even be safer.1 Even the alternatives can leach into your food, and I definitely wouldn’t feel comfortable drinking tea that contains plastics made from fossil fuels.

Although low-BPA epoxies exist and some are certified food safe by the FDA, in the end I wondered why I should spend so much time researching plastic epoxy when I can easily buy something plant-based from the urushi lacquer tree.

I cbf synthetic lacquer

As for cashew lacquer, I opted against it because it has synthetic materials mixed in. Just like epoxy, it would be too bothersome to research all the potential health effects of every cashew formula—especially when research on some compounds isn’t even conclusive yet. Urushi is, again, the simpler choice.

Urushi also has an impressive track record, spanning 12,000 years. It’s heat-proof, resistant to acids and bases, and 100% food safe after curing. Even if urushi takes longer to cure than epoxy, I think it’s worth it.

However, it’s toxic when raw and it can cause skin reactions, so wear gloves and ventilate the room when handling. You also have to be careful not to wash with an abrasive sponge, and it’s not microwave or dishwasher safe. Since my primary use is teaware, I’m fine with all that.

Process

To put it simply, Kintsugi has only four steps:

  1. Connect broken pieces
  2. Fill chips & cracks
  3. Paint lacquer
  4. Add gold dust

However, based on the complexity of the repair and the thickness of the ceramics, you’ll need to use different techniques.

General Theory

Urushi lacquer is combined with different materials to create adhesives, clay-like putty to fill cracks, and a surface for metal dust to adhere to. This is done in several steps with the lacquer recipe generally starting very thick and glue-like and moving to thin, paint-like consistency in the final layers.

Here are the ingredients you’ll probably use, ranked from most adhesive to least:

  1. Wheat flour
  2. Rice flour
  3. Sawdust
  4. Clay powder (jinoko)
  5. Clay powder (tonoko)
  6. Colored urushi (usually black or red pigment)
  7. Raw seshime urushi
  8. Transparent urushi

You don’t need to use all of these! In fact, I’m trying to use as few ingredients as possible to achieve maximum versatility for different kinds of breaks. That’s what I’m documenting in this series!

Example

Here’s an example of a very complex break:

  1. Connect broken pieces. Use either mugi urushi 麦漆 (wheat flour + lacquer) or urushi nori 漆糊 (starch glue + lacquer). In my post on Mugi-Urushi, I use a rice and wheat flour recipe. Curing time: ~2 weeks
  2. Fill large chips. Clean piece with sandpaper and acetone. Mix sawdust (kinoko) with urushi and stach glue to create a putty for large chips. This process is called kokuso.
  3. Fill small chips and cracks. Clean piece with wet sandpaper and acetone. Mix clay powder (tonoko) with lacquer to fill in cracks and chips. Curing time: 1 day. Repeat process several times until the finish is smooth.
  4. Paint base layer. Sand and clean the piece, then add black urushi base layer. Black urushi can be bought pre-mixed, or you can mix your own. Curing time: 1-2 days. Repeat several times to achieve a smooth finish.
  5. Paint finishing layer. Sand and clean the piece, then add red urushi in a thin layer. Red urushi can be bought or mixed from raw urushi and red powder. I recommend swatch testing to determine your urushi’s optimal powder application time.
  6. Add gold dust (optional). After red urushi is tacky, sprinkle gold dust and polish with a silk puff.

Materials

I explain a super simple and cheap setup in this post: Training Myself in Kintsugi. I think you can create a minimal setup with just one tube of urushi and some sort of flour/powder. I’ll keep experimenting to see if this is true or not.

Examples

Repaired with tonoko (sabi), raw lacquer, and red lacquer.

Process

  1. Fill with tonoko / urushi mixture (I used a q-tip). Sand.
  2. Paint seshime raw urushi as an underlayer. Sand. Repeat 3 times.
  3. Paint red urushi. Cure for 2 weeks.

Muro Box

See Muro

Mugi Urushi Recipes

See Mugi-Urushi

Common Mistakes

Lacquer too thick

Both of these problems arose from slopping on the red urushi way too thick.

It’s supposed to be a thin layer, but I went pretty wild with it. As a result, it didn’t cure long enough, and when I went to wash it I ended up bending the partially cured urushi (see left image). To ensure a reliable curing time, make sure the layers are applied thinly and evenly.

I poked it with my fingernail to test if it was finished—bad idea!! Now these indents are here forever.

A better idea is creating a paper test strip and using a q-tip, as suggested by Tokyu Hands.


Disclaimer

I am not fluent in Japanese. Any and all translations may be flawed. I’m just stumbling through these resources, tracing kanji into Google Translate, and using a dictionary app to supplement my rough understanding of the language. Forgive me for any mistakes. Thank you for reading!

Sources

  1. Are BPA Substitutes Any Safer Than BPA? - EPA