What happens when water meets Hagi-yaki: kan'nyū and nanabake, watched in real time

A Hagi-yaki glaze is never fully sealed. It develops a fine network of cracks called kan'nyū as it cools in the kiln, and through those cracks water, and later tea, slowly enters the clay beneath. That absorption, repeated over years, is what causes nanabake, the seven transformations Hagi ware is known for: a permanent, gradual darkening of the bowl's colour. Karahai, a related but separate effect, is the warm pink glow that appears where the glaze runs thin during firing itself, not from use.

I did something with this chawan I do not usually do on camera. I filled it with water and waited.

Within a minute, faint rings appeared across the surface, darker patches spreading out from small marks in the glaze, the kind of thing you would miss entirely if the bowl were dry. It is not damage. It is not a flaw. It is the clay doing exactly what Hagi clay has always done, and it is the clearest way I know to show what everyone means when they talk about nanabake without ever having seen it happen. So I got practical and got my bowl and camera out.

Water poured into Hagi-yaki chawan showing kan'nyū crackle glaze absorption, matcha bowl on tatami mat with gold folding screen background, Japan

Pouring water into a Hagi-yaki chawan to show how it moves through the kan'nyū crackle glaze, the same process behind nanabake.

The glaze is not sealed

Most ceramics are meant to keep liquid out. Hagi ware is not, not entirely. The glaze develops a fine network of cracks called kan'nyū as it cools in the kiln, tiny fractures where the glaze and the clay body shrink at slightly different rates. Under those cracks sits a soft, porous clay that has nowhere else to go but to absorb whatever meets it.

Pour water into a Hagi bowl and you are watching that structure work in real time. The water finds the kan'nyū, moves through it, and darkens the clay beneath. Give it a few minutes and the bowl looks like a different object, water gathered where the glaze is thinnest, spreading unevenly because no two cracks are the same.

Kan'nyū, nanabake and karahai: what is the difference?

I want to be precise about this, because it is easy to conflate the three.

  • Kan'nyū is the crack network itself, the physical structure in the glaze that makes everything else possible.

  • Karahai is a colour effect born in the kiln: a warm pink or blush that appears where the glaze runs thin during firing, present the day a piece leaves the kiln, unrelated to use.

  • Nanabake is what you are watching happen in these photos, except stretched over years instead of minutes: water, then tea, moving through the kan'nyū and staining the clay permanently.

What you see in these photos is temporary. The bowl will dry out over the next hours and return to how it looked before I touched it. This is also the whole reason why you need to let your chawan and yunomi dry before putting it back in the box. it'll keep the moisture inside if you don't.

Nanabake is not temporary. It is what happens after years of tea, not minutes of water, slowly staining the clay through that same network of cracks until the colour of the bowl has genuinely and irreversibly changed. This is how you can see if a bowl is heavily used or not when you pick it up.

But the mechanism is identical. Every cup of tea you drink from a Hagi bowl moves through the glaze exactly the way this water just did. Nanabake is not a separate process. It is this, repeated for years, with tea instead of water, until the staining stops washing out and starts staying.


Gohonte glaze, and what these four pieces reveal

These four unused pieces show something the water photos above do not: no two Hagi glazes start from the same place, and that starting point is exactly what will determine how each piece absorbs tea over the years ahead.

It starts even before the glaze, with the clay itself. Hagi-yaki is never made from a single clay, but from a blend of three: Daidō clay, low in iron and highly malleable, forms the grey-toned base of most pieces. Mishima clay, dug from an island off the coast, is coarser and much higher in iron, giving a reddish tone and a rougher, more absorbent texture. Mitake clay is fine and nearly white, closer to the kaolin used in porcelain, and is blended in to balance the other two. Every potter mixes these three in different ratios depending on what they want the finished piece to do, and that ratio already decides how porous, how coarse, and how ready to absorb liquid the clay body will be, long before it ever meets a glaze or a kiln.

Alongside kan'nyū and karahai, there is a third term worth knowing here: gohonte (御本手), a pattern of pale pink or white spots that appears where iron in the clay reacts during firing under a white slip, in reduction. The name comes from the Azuchi-Momoyama period, when Japanese tea masters sent order forms, gohon, to Korean kilns specifying the tea bowls they wanted, and the pieces that came back carried these characteristic spots. Unlike kan'nyū, gohonte is not a crack network, it is a colour pattern, closer in nature to karahai but visually distinct: gohonte shows as defined spots, karahai as a broader, softer glow.

Look closely at these four and you can already predict how each one will age. The piece with dense, deep-running kan'nyū has more surface for tea to reach, and will likely show visible staining sooner. The piece with strong gohonte spotting will keep those spots as a fixed point of contrast, the crackle around them darkening while the spots themselves stay put. The piece with the heavier white drip glaze will stain unevenly, following the exact pattern the glaze thickness laid down at the kiln.

None of this is predictable down to the precise shape it will take. That unpredictability is the point. But the underlying logic holds, all the way back to the clay bins these three earths sit in before a potter even touches the wheel: whatever the clay and the glaze do during firing sets the map that tea will later follow.

The three clays behind every Hagi piece: Daidō, Mishima, and Mitake, mixed in different ratios depending on what the potter wants the finished piece to do.


How different Hagi pieces will change with tea

A denser kan'nyū network, like the piece with cracks running deep across the whole interior, gives tea more surface area to work with, and will typically show visible staining sooner than a piece with sparse, fine cracking. A piece with strong gohonte spotting will keep those pink spots as a fixed feature, while the surrounding crackle darkens around them, so the contrast between spot and stain actually becomes more pronounced with age rather than fading. A piece with a heavier white drip glaze, where thick glaze meets thin, will often stain unevenly, following exactly the pattern the glaze thickness already laid down during firing.

None of this is predictable down to the exact pattern, that unpredictability is the point, but the underlying logic holds: whatever the glaze does at the kiln stage sets the map that the tea will later follow.

Why this matters if you own one

A Hagi bowl behaving like this is not a reason to worry. It is the reason people choose Hagi ware over a fully glazed piece in the first place. A bowl that develops with you, that carries a visible record of every pot of tea poured through it, is not damaged by that record. It is doing what it was made to do.

→ If you want to slow the process down and let it happen evenly rather than in patches, a good soak before first use helps the water fill the cracks gradually instead of finding one weak point first. I cover that, along with the rest of what a Hagi piece asks of you, in the care guide for chawan, yunomi and vases.

→ Want the fuller story on why Hagi ware ages this way, beyond just the mechanism? Read the full Hagi-yaki journal piece.


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One of my favorite mornings in Hagi: come with me to the Okada kiln