Japanese Pottery Glazes: The Main Types Explained

Two tea bowls of the same shape can stand side by side and still differ in color, piece by piece and maker by maker. That is one of the pleasures of Japanese ceramics. One a deep blue, the other a warm amber.

What decides that difference in color is the glaze — the glassy film that covers the surface. Glaze does not only give a piece its color; it makes the piece more watertight, makes it stronger, and creates the very texture that meets the user's hand. It is no exaggeration to say that glaze decides much of the impression a piece of pottery leaves.

This article explains what glaze is, how to recognise the main glazes, and the pleasure of choosing pottery by glaze. By the end you should be able to pick up a piece and say, this is Oribe, or, this crazing is going to develop.

What glaze is

A film of glass covering the piece

Glaze is a material applied to the surface of a formed and bisque-fired piece which turns glassy when fired at high temperature.

A piece fired from clay alone has a surface full of fine pores. Left that way it takes in water and holds odours. Apply glaze and fire it and the surface melts into a film of glass, so the piece passes no water, resists staining and washes easily. Glaze was first of all a technology for practical use.

But it did not stop there. The trace metals in the raw materials produce unexpected colors in the flame. The same glaze changes expression with the thickness applied and its position in the kiln. That impossibility of full control is what pushed glaze from a practical technology into the territory of beauty.

What glaze is made of

The basic materials of glaze divide broadly into three.

• 1. Feldspar　The main component, which builds the glass structure. It melts at high temperature and becomes glass.
• 2. Ash and lime　Feldspar alone would need close to 1,500°C, so these lower the melting temperature. Ash from burnt plants — wood ash, straw ash — has been used since ancient times, and the type of ash also changes the color.
• 3. Metals (colorants)　The components that decide color. Tiny quantities change it dramatically.

What is interesting is that the same iron produces entirely different colors. In small amounts iron gives blue-green; in larger amounts, black. The quiet blue of celadon and the deep black of tenmoku — these two opposites come from the same metal. And beyond the components of the glaze materials, the components in the clay also greatly change how color emerges. Glaze, clay, and the oxidation or reduction described below work as a set to create the character particular to each maker's work.

The air in the flame changes the color: oxidation and reduction

The other element deciding the color of a glaze is the air inside the kiln during firing. How the air meets the work greatly changes the color the glaze components give.

• Oxidation firing　Firing while feeding the kiln plenty of oxygen. Glazes come out in warm colors: red-brown, yellow, bright green.
• Reduction firing　Firing with the oxygen restricted. Starved of oxygen, the flame takes oxygen from the clay and the glaze. Through that action iron shifts to blue-green and copper to red, producing the cool, clear colors of ash-blue and celadon. Blue pieces are usually fired this way. And as oxygen is drawn from the clay, the components the clay holds also shift the color.

The same clay and the same glaze become a different piece through this difference in air alone. That is why celadon can only be born in reduction. Makers watch the kiln's temperature and air for days on end because everything rests on this single point.

How the glaze is applied changes the expression

Glaze also changes greatly with how it is applied. When you look at a piece, try to find the traces of the application.

• Dipping　The most basic method: the whole piece is dipped into the mixed glaze. The finish is even, but the places held by the fingers take no glaze and those marks can remain. Some makers leave these finger marks as one form of keshiki.
• Ladling　Glaze scooped in a ladle and poured over the piece from above. The path it runs becomes the pattern itself, carrying momentum and chance.

• Spraying　Applied as a mist. Gradations of density become possible.
• Multiple glazes　Two or more glazes applied to one piece. At the boundary they melt into each other and unexpected colors appear.
• Wax resist and sgraffito　Drawing patterns by making waxed areas repel the glaze, or by scraping applied glaze away to reveal the ground beneath.

There is also the choice of applying no glaze at all. yakishime, represented by Bizen and Shigaraki, uses no glaze and fires hard at high temperature. Even so, a natural glaze appears on the surface where wood ash has settled and melted. Not a glaze applied by a person, but a glaze applied by the kiln.

Recognising the main glazes by color

From here we introduce the main glazes color by color, so that you can name them when you actually see a piece.

Blue glazes

celadon is the clear color, from blue-green to pale blue, produced by reduction-firing a glaze holding trace iron. Originally a Chinese technique, in Japan it passed down through Nabeshima and Kyoto ware. The appeal of celadon lies in depth rather than color itself. Where the glaze pools thickly it is dark, where it thins it is pale, and the expression shifts with the fall of light. Most celadon carries fine crazing, and time accumulates in it.

Sometsuke and gosu describe the technique of painting on a white body with a cobalt pigment and firing a clear glaze over it. The design, drawn in a single indigo, appears to sit sunk beneath a transparent film. It is the expression that represents the porcelain regions — Arita, Hasami, Tobe. Gosu is the painting pigment, and the leading example of underglaze painting.

Ruri glaze mixes cobalt into the glaze itself, dyeing the whole piece a deep navy. It is a night-sky blue, and combined with gold it becomes strongly showy.

Green glazes

Oribe is a vivid deep green from a copper-bearing glaze. It is a Mino glaze born in the Azuchi-Momoyama period from the eye of the tea master Furuta Oribe. Its essence is a bold composition that does not glaze the whole piece green but covers only part of it, drawing designs in iron across the rest. Asymmetry, distorted forms, deliberate breaking of harmony — revolutionary at the time and avant-garde even now. The gradations of green, and the depth where it has run and pooled, are what to look at.

Ash glaze, made mainly from plant ash, is the oldest glaze of all. It comes out from pale yellow-green to olive, giving a plain, settled impression. It is the glaze that sits most naturally on everyday pottery.

White glazes

Shino is the first white glaze born in Japan, made mainly from feldspar. It comes from Mino. Shino white is not the pure white of porcelain but a thick, plump white carrying a faint red or yellow. Countless fine pores called yuzuhada (citron skin) open across the surface, and the "fire color" where iron in the ground shows through red becomes its scenery. It is soft in the hand and warm at the lip. Shino is a piece to touch as much as to look at.

kohiki covers a dark, iron-bearing clay with white slip and finishes with a clear glaze. It is a soft milky white with the color of the ground clay showing through in places. Kohiki absorbs readily, and stains of tea and soy sauce enter it as scenery the more it is used — one of the glazes that develops most of all.

hakeme applies white slip with a coarse brush and leaves the brush marks as they fall. Vigorous white streaks run across the piece.

Yellow glazes

Ki-Seto is the pale, subdued yellow obtained by oxidation-firing an ash glaze. It is a leading Mino glaze. The surface has a moist, settled quality, and the skin known as aburage-de (fried tofu skin) is held to be the finest. Green speckles (tanpan) and scorch-like bleeds of iron add scenery to an otherwise quiet piece.

Black and brown glazes

Tenmoku and iron glazes give black to dark brown from a glaze high in iron. The name derives from the tea bowls used in the Zen temples of Mount Tianmu in China. Special changes can occur in tenmoku: yuteki (oil spot), where the iron in the glaze crystallises into speckles, and yohen, where an iridescent shimmer appears depending on the angle of light. Yohen especially, with only a few complete surviving examples said to exist in the world, is the summit of glaze.

Ame glaze, obtained by applying an iron glaze thinly and firing in oxidation, gives a translucent amber. As the name suggests, it is a glossy brown recalling malt syrup. Not as heavy as tenmoku, it is widely loved as an easy color for everyday pottery.

Red glazes

Shinsha is the red to red-purple born by reduction-firing copper. The same copper turns green in Oribe and red in shinsha. The change is extremely unstable, and the slightest deviation in kiln conditions makes the color vanish. Not even the maker knows the result until it comes out — one of the most temperamental glazes there is.

akae is the overglaze painting technique of painting in colors led by red over a glazed and fired piece, then fixing it at low temperature. It is the showy world of polychrome enamel represented by Kutani and the Kakiemon style.

Glazes that appear as changes on the surface

Crazing is the fine cracking that enters the glaze surface through the difference in shrinkage between glaze and body. It is not breakage. It does not affect the strength of the piece, and in Japan it has long been loved as scenery. It is conspicuous on Hagi ware and on celadon. As tea and coffee soak in with use, the lines of the crazing rise darker — a change called keinen bika.

bidoro is what forms when ash settles thickly in a wood kiln, melts, and pools in a vivid, glassy green. The name comes from Portuguese vidro, glass. It is prized on Iga and Shigaraki ware.

Crystalline glaze produces crystals in the glaze as it cools, raising patterns like flowers. No two ever take the same shape.

Choosing pottery by glaze

Now to the main subject. The point is not to memorise the names of glazes. The point is to become able to choose pottery that suits your own life. Three angles help.

1. Choose by what you will serve

Pottery is not complete on its own. It is completed only when food goes into it. The color of a glaze can lift the color of the food, or kill it.

The principle when in doubt is this. If the food is rich in color, let the piece stay quiet; if the food is poor in color, let the piece speak. Choosing white — kohiki or shino — as a first piece will not go wrong.

2. Choose by whether you want change

There are two kinds of pottery: the kind most beautiful on the day you buy it, and the kind that grows more beautiful with use.

Porcelain sometsuke and ruri glaze are the former. The beauty of the day you bought it is kept exactly ten years on. Clean, stable, supporting the daily life of a household.

Kohiki, Hagi ware and crazed pieces are the latter. Kohiki that begins almost blankly white raises brown mottling after a year, and after three years settles into amber overall. This change is called keinen bika. Two people who bought the same piece own entirely different pieces three years later — because how it was used becomes, directly, the expression of the piece.

Neither is superior. But buying without knowing which you want leaves you puzzled later.

3. Choose by who made it

Last, and perhaps this is the most important angle.

Celadon, Oribe, kohiki: these are names of techniques, not names of works. Even within celadon, the blue differs completely from maker to maker. The mixing of the glaze, the thickness applied, the temperature and duration of firing, where in the kiln it is placed — all of it is the maker's judgement, and the accumulation of it makes that person's blue.

One maker fires celadon in a pale color as close as possible to white. Another pursues a deep, green-leaning blue. Grouped under the same phrase, "a celadon tea cup," they are different things in the hand.

So when you choose from among the pieces a glaze-name search turns up, look further, to who made it. Why that person is pursuing that color, in what kind of kiln they fire. A piece chosen with that much understood is not merely "a celadon tea cup" but the one piece you chose.

Looking for pottery by glaze

Nokaze carries the work of makers engaged with each of these glazes — celadon, Oribe, shino, kohiki, tenmoku, ame. For every one of them, you know the maker's name and the maker's own words. Even within celadon, you can see whose blue it is before you choose.

Which color suits your table? Begin simply by looking.

Related guides

• Crazing (Kannyu): Cracks in Glaze That Aren't Damage
• Keshiki: How to Read the 'Landscape' on a Pot
• How to Care for Japanese Ceramics: A Practical Guide

Pieces available at Nokaze

• Japanese Blue and White Pottery | Hand-Painted Sometsuke
• Yakishime | Unglazed Japanese Stoneware Fired in Wood Kilns