My Japanese tea bowl is leaking: is this normal, and what should I do?
Kogechan had prepared everything perfectly.
The matcha. The chasen. The hot water. His beautiful chawan placed on the table.
And then... a small wet halo appeared under the bowl.
Is it broken? Is it a crack? Did the artisan mess up the firing?
Not necessarily.
Some Japanese tea bowls can absorb water and seep slightly without being defective. This is particularly known for certain ceramics like Hagi-yaki, Raku, or Shigaraki. In such cases, a traditional treatment called medome (目止め) can help reduce the phenomenon.
However, if water quickly drains through an actual crack, that's another story.
So, before calling for help or turning your chawan into a pencil holder, here's how to diagnose the issue.
Step 1 — Is my chawan seeping or is it really cracked?
Start by filling your perfectly dry bowl with moderately warm water and place it on a dry surface.
Then observe.
| What you see | Possible cause | What to do? |
|---|---|---|
| The side or foot gradually darkens | The clay absorbs water | Generally normal for porous ceramics |
| Diffuse moisture appears on the outside with droplets, the bowl "sweats" | Seepage related to the clay and firing | A medome can be useful |
| There are fine cracks in the glaze | Kannyū 貫入 | Not necessarily a defect |
| Water follows a precise line or a drop always appears in the same spot | Possible crack | Inspect the bowl and stop using hot liquids |
| Water quickly passes through the wall in a few seconds | Probable structural crack | Do not use the bowl for drinking |
Beware of kannyū
The kannyū (貫入) are the fine cracks observed in the glaze of many Japanese ceramics.
They appear when the glaze and the body of the bowl do not contract in exactly the same way during cooling.
A network of kannyū can be perfectly normal, even aesthetically sought after. A craze in the glaze is therefore not automatically a crack passing through the bowl.
However, if the water clearly follows a line and quickly passes through the wall, be cautious.
And let's remember an essential rule right away:
Medome can reduce the seepage of porous clay. It does not repair a real crack.
Step 2 — Why do some Japanese bowls let water through?
Ceramics are not always as impermeable as glass.
Depending on the clay used and the firing temperature, it is more or less vitrified. Some pottery retains tiny spaces in its structure where water can penetrate.
This explains why a bowl can darken when it comes into contact with water, absorb liquid, or sometimes show slight moisture on the outside.
To better understand the different clays, firings, and glazes, you can also consult our guide to Japanese ceramics: styles, clays, and regions.
Hagi-yaki, the textbook case
Hagi-yaki (萩焼) is probably the most well-known Japanese ceramic for this phenomenon.
Its traditionally quite absorbent clay can let water and tea penetrate. This is not necessarily considered a defect: Hagi is precisely famous for the way it evolves with use.
Over time, tea penetrates the tiny interstices and cracks in the glaze, gradually changing the appearance of the bowl. This transformation is called Hagi no nana bake (萩の七化け), the "seven transformations of Hagi."
Repeated use can also help reduce certain seepages by gradually filling some of these interstices.
In other words: a new Hagi that shows a little moisture is not necessarily a failed Hagi.
What other bowls can seep?
Raku-yaki (楽焼) chawans can also be soft and absorbent, as can some pieces of Shigaraki-yaki (信楽焼) type.
Kohiki (粉引) can also be susceptible to absorption depending on the clay and manufacturing. A small clarification: unlike Hagi or Shigaraki, Kohiki does not refer to a ceramic region, but a technique in which dark clay is covered with a white slip.
However, beware of shortcuts.
A Bizen-yaki (備前焼), for example, is traditionally unglazed but fired very strongly at very high temperatures, which creates a vitrification phenomenon and makes the bowl waterproof. Unglazed therefore does not automatically mean porous.
And Japanese porcelain, much more vitrified, is generally very non-absorbent. If you want to distinguish Arita, Imari, Kutani, or Nabeshima, we have dedicated an entire article to the history and techniques of Japanese porcelain.
In short: it is not the rustic appearance or the absence of glaze that alone determines whether a bowl is likely to seep. It is rather the clay it is made of and the firing it has undergone that determine its porosity.
Why isn't this necessarily a problem during the chanoyu tea ceremony?
Because a chawan is not a carafe.
During chanoyu, matcha is prepared and then drunk quickly. The liquid therefore does not stay in the bowl for long.
This is particularly evident with Hagi and Raku: despite their sometimes absorbent nature, these ceramics are historically intimately linked to the tea ceremony and are the most prized types of chawan.
Slight moisture can therefore be compatible with the normal use of a chawan and sometimes even sought after.
A big leak, no.
Matcha is supposed to end up in your stomach, not on the tatami.
There's still a limit to wabi-sabi.
Step 3 — Perform a medome to reduce seepage
If your chawan is simply porous and has no structural cracks, you can consider a medome (目止め).
The principle is simple: a starch-rich preparation, usually rice-based, is used so that the starch penetrates some of the tiny interstices in the clay.
Medome can thus reduce absorption and certain seepages.
There are several methods. For a Hagi, one can notably use a preparation called omoyu (おもゆ): a kind of slightly thickened, starch-rich rice cooking water.
How to make a gentle omoyu medome?
- Inspect the chawan. If it has a real crack, an old repair, or significant fragility, do not perform a medome without identifying the problem.
- Prepare the omoyu. Cook a small amount of rice or already cooked rice in a lot of water—about ten times its volume—to obtain a slightly thickened whitish liquid.
- Let the preparation cool. Avoid any thermal shock, especially with an old piece.
- Fill the chawan with omoyu and let it sit for about half a day to a full day.
- Empty and rinse the bowl thoroughly with clear water.
- Let it dry completely in a well-ventilated area before using or storing it.
If a Hagi continues to seep, the treatment can be renewed.
For old or vintage chawan, we prefer this cautious approach rather than systematically boiling the piece in a pot. An old ceramic already has a history: shock, restoration, or fragility are not always visible at first glance.
If your chawan comes from KOGEDO and you're unsure, you can simply send us some photos before playing apprentice alchemist.
Rice water, omoyu, katakuriko… what are the other methods?
There is no single medome recipe.
Kome no togijiru (米のとぎ汁) is the whitish water obtained when rinsing raw rice. Some medome methods involve immersing the ceramic in it and then gently heating the whole.
Omoyu (おもゆ) is obtained by cooking rice in a lot of water. This is the gentle method we just saw.
Methods using katakuriko (片栗粉), a starch, or traditionally funori (布海苔), derived from an algae used as a binder, are also found.
The principle always remains the same: to introduce a substance capable of reducing the spaces through which the liquid circulates.
Is medome hygienic?
Yes, if done correctly.
After a rice or starch treatment, you simply need to rinse the chawan well and, most importantly, let it dry completely.
This is important for all absorbent ceramics: a still-damp clay piece stored in a cupboard or its tomobako can encourage bad odors and mold.
No need to disinfect your bowl like an operating room.
Rinse, dry completely, and it's good to go.
Should all Japanese tea bowls undergo medome?
No.
Porcelain or highly vitrified stoneware generally does not need it. Some bowls have also already been treated by their artisan, while others are meant to evolve naturally with use.
Medome is therefore a solution for certain absorbent ceramics, not a mandatory ritual to impose on every chawan you encounter.
What's next?
Once your chawan has been used, rinse it with clear water and let it dry completely before storing it, especially if it is an absorbent clay.
And if your Hagi gradually changes color over the course of matcha bowls, don't necessarily try to restore its original appearance.
It may simply be doing what Hagi have done for centuries: aging with you.
This is also what we love about old and handmade Japanese objects at KOGEDO. They don't always try to hide time.
They tell its story.
And if all this has made you want to take a closer look at some bowls, you can browse our Japanese Tableware Arts collection, where chawan, yunomi, ceramics, porcelains, sake items and other finds from Japan mingle.
In summary
Your bowl gets slightly damp? It might simply be porous.
Is it a Hagi, a Raku, or another absorbent clay? The phenomenon might be part of the ceramic's characteristics.
No crack? A medome can help reduce the seepage.
Water quickly passes through a precise line? Then stop: it's probably no longer just a matter of porosity.
So, a chawan that sweats a little isn't necessarily broken.
But a chawan that tries to fill the saucer on its own still deserves a serious inspection.