Ceramics｜Japan Kogei Association

Introduction

The history of Japanese ceramics can be traced back over 10,000 years to the early part of the Jomon period (10,500-300 BC) when unglazed earthenwares known as Jomon wares (Jomon doki) were first produced.
The introduction of agriculture from continental Asia during the succeeding Yayoi period (300 BC-AD 300) was accompanied by the appearance of different kinds of unglazed earthenware known as Yayoi wares (Yayoi doki).
Stoneware production started in Japan with the manufacture of Sue wares (Sueki) in the late 4th to early 5th century.
The necessary technologies, which included the use of the potter's wheel and kilns capable of reaching stoneware temperatures, were introduced from the continent.
Sue wares were made up to and during the Heian period (794-1185).
During the Nara period (710-794) low-fired pottery with artificially applied glaze known as Nara three-coloured ware (Nara-sansai) was also made.
Ceramics with high-fired ash and iron glazes were first made during the Kamakura (1185-1336) and Muromachi (1336-1573) periods.
The Azuchi-Momoyama period (1573-1615) saw the rise of the tea ceremony and the emergence of revolutionary new forms of ceramics reflecting the wabi and sabi aesthetics of the tea masters of the time.
Successive advances in technology during the following Edo period (1615-1868) resulted in the widespread expansion of Japan's ceramics industry.

Kaneshige Toyo Bizen mimitsuki mizusashi (Fresh-water jar for the tea ceremony, Bizen ware) This dynamic but understated fresh-water jar is a particularly successful example of the kiln change (yohen) effect characteristic of Bizen wares.

（The National Museum of Modern Art, Tokyo）
Tomimoto Kenkichi Iroe kinginsai shibenkamon kazarizara (Dish, porcelain with floral patterning painted in overglaze enamels, gold and silver) A richly ornate work decorated with Tomimoto's original shibenka (four-petal flower) motif in overglaze gold and silver.

（The National Museum of Modern Art, Tokyo）

In 1616 porcelain stone, the raw material of porcelain, was discovered in Arita, Saga Prefecture, by Korean potters who had moved to Japan, allowing porcelain to be produced for the first time in Japanese history.
Subsequently, from the 18th century onwards, new ceramic-producing centres were established all over the country.
The Meiji period (1868-1912) witnessed the introduction of new technologies that resulted in increasing mechanization of ceramic production.
These included the use of plaster moulds for forming and coal-firing kilns.
At the same time there was the emergence of individual artist potters who employed a wide range of techniques to produce many different kinds of ceramic art.

Ishiguro Munemaro Kokuyu katsuhan chomon tsubo (Black-glazed jar with bird motifs set against patches of brown) The freely rendered bird motifs were achieved by using wax resist on an underlying black glaze prior to the application of patches of brown glaze.

（The National Museum of Modern Art, Tokyo）
Kato Hajime Moegi kinrande marubako (Round box, porcelain with pale green glaze and overglaze decoration in gold) This richly ornamented box has kinrande decoration, a technique involving the use of gold leaf, over a pale green ground.

（The National Museum of Modern Art, Tokyo）

Centres of ceramic production

Japan has many ceramic-producing centres, each of which has its own history and characteristics.
Agano = The Agano kilns were originally established by potters from Korea. Ceramics from Agano are characterized by a greenish glaze. (Fukuoka Prefecture)
Arita = Japan's first porcelain was produced in Arita after Ri Sanpei's discovery of porcelain stone in about 1616. Ko-Imari, Kakiemon and Nabeshima porcelains are all varieties of Arita ware, also known as Imari ware. (Saga Prefecture)
Iga = The Iga kilns are famous for the tea ceramics with a distinctive bluish-green glassy glaze they used to produce. They are located next to the Shigaraki kilns. Due to the similarity of the clays used, Iga and Shigaraki wares resemble each other closely. (Mie Prefecture)
Izushi = Izushi wares are distinguished by the use of carved and pierced patterning on a translucent white porcelain body. (Hyogo Prefecture)
Echizen = The Echizen kilns are well-known for having produced simple unglazed storage jars and mixing mortars for everyday use. (Fukui Prefecture)
Kasama = The Kasama kilns made sturdy everyday vessels such as storage jars, mixing mortars and teapots. (Ibaraki Prefecture)

Nakazato Muan Kikaratsu tataki tsubo (Jar, Yellow Karatsu ware) Jar fashioned using the historical Karatsu method of coil-building and beating with a paddle. The shape is built up with ropes of clay that are coiled on top of each other. A wooden support is then pressed against the inner wall as the outside is beaten with a paddle.

（The National Museum of Modern Art, Tokyo）

Karatsu = Karatsu flourished as a ceramic-producing centre at the end of the 16th century. The local clay is very sandy and contains a high percentage of iron. The subdued quality of Karatsu wares has been much appreciated by devotees of the tea ceremony. The main varieties are Painted Karatsu ware (egaratsu), Mottled Karatsu ware (madaragaratsu) and so-called Korean Karatsu ware (Chosen-karatsu). (Saga Prefecture)
Kyoto = Kyoto ware (Kyoyaki) is a general term referring to all ceramics produced in Kyoto. Kyoto produces a great variety of ceramics using a wide range of different techniques and styles. (Kyoto Prefecture)
Kutani = The Kutani kilns are famous for their richly coloured porcelains decorated in thick overglaze enamels. The five Kutani colours are red, yellow, green, purple and dark blue. (Ishikawa Prefecture)

Shigaraki = A long-established pottery centre producing unglazed stoneware whose rough, orange-firing clay gives it a characteristically rustic feeling. (Shiga Prefecture)
Seto = Blessed with rich deposits of high quality gairome and kibushi clays, this long-established pottery centre produced ash- and iron-glazed ceramics for many centuries. In the late Edo period Seto became an important centre for porcelain production. It now produces ceramics of all different kinds. (Aichi Prefecture)
Tamba = Tamba has long been an important centre for the production of simple everyday items such as storage jars and mixing mortars. Its highly iron-bearing clay fires a characteristically reddish brown colour. (Hyogo Prefecture)
Tokoname = Tokoname is well known for its ash-glazed ceramics and also for its teapots made of fine iron-bearing shudei clay. (Aichi Prefecture)
Tobe = The most active ceramics centre in the Shikoku region, Tobe has been a major producer of porcelain decorated in underglaze blue since the Edo period. (Ehime Prefecture)
Hagi = Hagi is famous for its Korean Chosen period style ceramics made from soft, pervious daido clay covered in a milky white glaze. (Yamaguchi Prefecture)
Banko = During the Edo period Banko was an important producer of stoneware decorated in overglaze enamels. Nowadays it is best known for its unglazed dark brown teapots made from iron-rich shidei clay. (Mie Prefecture)

Arakawa Toyozo Shino chawan (Tea bowl, Shino ware) Tea bowl made from slightly rough mogusa clay covered in a thick coating of Shino glaze.

（The National Museum of Modern Art, Tokyo）
Ezaki Issei Kaiyu kaki (Flower vase, ash glaze) Vase of Tokoname clay with ash glaze applied to the rim fired in a carbonising atmosphere in the manner of ancient Sue wares.

（The National Museum of Modern Art, Tokyo）

Bizen = The highly plastic, iron-rich clay used to make Bizen ware is found in rice paddies. It is fired unglazed for an extended period so as to allow the innate quality of the clay to reveal itself to best effect. (Okayama Prefecture)
Mashiko = Mashiko is known for its sturdy, simple ceramics in Mingei(Folk Craft) style. (Tochigi Prefecture)
Mino = During the Momoyama period the Mino kilns produced a wide variety of ceramics such as Kiseto (Yellow Seto), Setoguro (Black Seto), Shino and Oribe wares for use in the tea ceremony and as high-quality tablewares. Mino now produces ceramics of all different kinds. (Gifu Prefecture)

Shimizu Uichi Kakiji kokusenmon hachi (Bowl, black lines on a persimmon-glazed ground) Bowl covered in persimmon glaze over which a secondary glaze has been partially applied to create a spiral pattern.

（The National Museum of Modern Art, Tokyo）

Basic ceramic types

Ceramics are generally classified into four main types; doki (unglazed earthenware), sekki (stoneware), toki (pottery) and jiki (porcelain).
Doki = Unglazed and fired at a low temperature of between 500 and 900?, the body is porous and highly pervious to water.
Sekki = Unglazed and fired to between 1200 and 1300?, the body is a vitrified and almost completely impervious to water. Examples include Tokoname and Bizen wares.
Toki = Glazed and fired to between 1100 and 1250?, the body is porous and pervious to water. Examples include Karatsu, Hagi and Mashiko wares.
Jiki = A mixture of kaolin and porcelain stone fired to between 1250 and 1350?, the body is vitrified and impervious to water. It is white and lustrous, and gives out a metallic ring when tapped. Examples include Arita and Kutani wares.

Clays and forming techniques

Clay is prepared by the crushing and pulverization of the raw materials followed by sieving and filtering, the exact process varying on the quality required for the purpose at hand. Before clay can be used it has to be thoroughly tempered by wedging. This dispels trapped air bubbles and evens out irregularities in the hardness of the clay such as would result in damage occurring during firing. The main forming techniques are as follows:
Tebineri (hand-pinching) = A forming technique that involves no tools and relies solely on the use of the potter's hands.
Himo-zukuri (coil-building) = A forming technique in which ropes of clay are coiled on top of each other, the joints between them being firmed with the fingertips or a spatula. The shape is refined by beating the exterior with a racket-shaped paddle.
Tatara-zukuri (slab-building) = Slabs of clay sliced from a block are assembled to form geometric shapes or bent around to create cylindrical vessels.
Kata-zukuri (mould-forming) = A forming technique involving the use of clay or plaster moulds.
Rokuro-zukuri (wheel-throwing) = A forming technique in which clay centred on a revolving wheel is pulled upwards with both hands and fashioned into the desired shape. The technique is particularly suited to the making of round vessels.

Decorating techniques

Ceramics are decorated with a variety of techniques such as:
Rinka = The indentation at regular intervals of the rim of a dish or bowl to give the appearance of a circular flower.
Warikodai = A foot ring on a tea bowl with cut-away sections.
Chomon = Carved decoration involving the use of planes and other tools on a fully dried clay form.
Inka = Stamped decoration.
Zogan = Inlaying of carved or stamped indentations with clay of a different colour from the main body of a piece.
Sukashibori = Pierced patterning.
Nerikomi = Addition of metal oxide to colour the clay.
Neriagete = Layering or blending of clay of different colours to create a striped or marbleised effect.
Keshogake = Application of white slip to whiten the underlying clay body.
Hakeme = Application of slip by brush.
Deisai = Application of slip pigmented by the addition of metal oxide.
Shitaetsuke = Painting in metal oxides on the biscuit-fired body prior to the application of clear glaze and high-temperature firing. The main types of underglaze decoration are sometsuke (cobalt blue), tetsue (iron brown) and yuriko (copper red).

Suzuki Osamu Shino zogan kaki (Flower vase, inlaid decoration, Shino ware) The red slip covering applied to the vase was partially scraped away to reveal bands of the underlying white clay body. Iron brown stripes were then painted on to enhance the rhythmic effect of the design.

（The National Museum of Modern Art, Tokyo）

Glazing techniques

High Temperature Glazes
A glaze is a glassy film that covers the surface of a clay body, preventing it from absorbing water and providing decorative effect. Glazes fluxed with lead or soda are fired to temperatures of between 700 and 1100?. Low temperature glazes of this kind are often very colourful. Glazes in which feldspar is mixed with ash, limestone and metallic ores are fired to between 1200 and 1300?. These are known as high temperature glazes. Examples of high temperature glazes are as follows:
Ameyu = Amber glaze, the light brown colour of which derives from the inclusion of iron in the glaze mixture.
Irabo = A brownish yellow glaze made by mixing iron-rich clay with wood ash.
Ofuke = A light yellowish-green glaze whose name derives from the Ofuke-yaki (Ofuke ware) formerly produced under the patronage of the Owari Tokugawa family.
Oribe = A bluish-green glaze whose colour is the result of oxidation firing of a copper-containing glaze mixture. The name has its origin in Oribe-yaki (Oribe ware).
Kaiyu = Wood ash glaze.

Arakawa Toyozo Setoguro chawan (Tea bowl, Setoguro (Black Seto) ware) Amply coated with an iron-rich glaze, this tea bowl has been taken out of the kiln at the height of the firing and quickly cooled in water. The main feature of this piece is its subdued jet-black colouring.

（The National Museum of Modern Art, Tokyo）

Kiseto = The main feature of Kiseto (Yellow Seto) is its soft, rich yellow colouration resulting from the oxidation of an iron-rich glaze mixture.
Kinyo = Jun ware style silica-rich celadon glaze with a milky lavender colour.
Kokuyu = Iron-rich glaze that turns black when fired.
Shizenyu = Natural ash glaze caused by ash from the wood used to fire the kiln settling on the surface of the pot. Lime from the ash and feldspar from the clay body fuse together to form a glaze. This is sometimes referred to as kaiyu (wood ash glaze).

Miwa Kyusetsu XI Onihagi warikodai chawan (Tea bowl, warikodai type foot, Onihagi ware) The clay used for the body of this tea bowl contains a high proportion of coarse sand. The white glaze is very thickly applied. The foot (kodai) has several cuts (wari) in it, hence the term warikodai.

（Private Collection）
Shimizu Uichi Tetsuyu henko (Jar, iridescent iron glaze) Patterns were drawn by finger into the iron-rich glaze while it was still wet.

（The National Museum of Modern Art, Kyoto）

Shino = White glaze made almost entirely of feldspar.
Shinsha = A bright red glaze achieved by reduction firing of a copper-containing glaze mixture.
Seiji = Celadon, the light blue colour of which is achieved by reduction firing of an iron-containing glaze mixture.
Seihakuji= Pale blue porcelain glaze whose colour is the result of minute quantities of iron in the glaze mixture. The alternative name inchin (blue shadow) derives from the way in which the glaze that accumulates in the incised and carved areas of the clay surface is darker than elsewhere.
Setoguro = The main feature of Setoguro (Black Seto) is its jet-black colouring, which is due to the high iron content of the glaze mixture. Pieces are taken out of the kiln at the height of the firing and cooled in water. Hikidashiguro (lit. 'pulled-out black') is an alternative name.
Chosen-karatsu = Literally 'Korean Karatsu', this is a kind of Karatsu ware on which milky white straw ash glaze and black glaze are used in combination.
Tenmokuyu = A general term used for iron glazes that fire a dark brown colour. These include kokuyu (black glaze), kakiyu (persimmon glaze) and bekkoyu (tortoiseshell glaze). The name Tenmoku is derived from so-called Tenmoku tea bowls from China.
Tomeiyu = Lustrous, transparent glaze through which underglaze painting is clearly visible.
Hakuji = White porcelain covered in a transparent glaze.
Yuriko = Painted decoration in underglaze copper red.

Hara Kiyoshi Kinyobachi (Jun ware style bowl) A thick layer of glaze containing a large quantity of silica gives this bowl a distinctive milky lavender colour. The reddish-purple colouring is caused by the presence of copper.

（The National Museum of Modern Art, Tokyo）
Miura Koheiji Seiji rinka hachi (Bowl with foliated rim and a celadon glaze) A special kind of iron-rich clay called mumy?i from Sado Island (Niigata Prefecture) has been used to make this bowl. Crackles can be seen on the glaze surface.

（The National Museum of Modern Art, Tokyo）
Tsukamoto Kaiji Seihakuji ozara (Large dish, porcelain with a pale blue glaze) The colour is darker where the glaze has pooled at the bottom of the dish and on the inner edge of the rim.

（The National Museum of Modern Art, Kyoto）

Uwaetsuke (Overglaze Enamel Painting)
Overglaze enamel painting is a decorating technique that involves the application of overglaze enamels to the surface of a glazed vessel that has already been fired to a high temperature. Overglaze enamels consist of a transparent glass-like substance (frit) mixed with lead and silica fused on in a secondary low temperature (750-850?) firing. The addition of iron gives a red or yellow colour, copper gives green, manganese purple, and cobalt dark blue. After Sakaida Kakiemon I mastered the technique of painting overglaze enamels on to a white porcelain body in Arita in about 1647, potters began to produce a variety of richly enamelled porcelains in the form of Kakiemon, Iro-Nabeshima and Old Kutani wares. The combination of gold and silver with red, yellow, green, dark blue and purple enamels makes the possibilities for opulent decoration much greater than with glazes or underglaze painting.
Varieties of overglaze enamel painting are as follows:
Iroe = Patterns are painted in red, yellow, green, dark blue and purple on to the surface of a previously glazed and high-fired piece of pottery and fused on by firing again at a low temperature. Alternative names are akae, uwaetsuke, gosai and nishikide.
Iro-Nabeshima = During the Edo period, elaborate, stylishly decorated porcelain made with superior techniques from the finest materials were made as official gifts for presentation by the Nabeshima clan. When red, green or yellow colours are applied over motifs painted in underglaze blue, the term Iro-Nabeshima is used. The Imaizumi Imaemon family of Arita preserves this traditional technique.

Tomimoto Kenkichi Akaji kinginsai shidamon kazaritsubo (Covered jar, stylized fern pattern, gold and silver painting on a red enamel ground) A magnificent piece of iroe, the fern pattern is painted in overglaze gold and silver over a red ground.

（Nara Prefectural Museum of Art）
Fujimoto Yoshimichi Iroe ginsai nemu sojakuzu hako (Box, sparrows among branches of a silk tree, painting in overglaze enamels and silver) A realistic depiction of a pair of sparrows in a silk tree executed in a rich palette of overglaze colours.

（The National Museum of Modern Art, Kyoto）

Kakiemon = Kakiemon wares are distinguished by the use of red, blue, yellow, purple and black enamels on a milky white co-called nigoshidebody. The Sakaida family has used the Kakiemon name for many generations and any iroe porcelain produced by this family is referred to as Kakiemon ware.

Kato Hajime Iroe kinsai kikumon mizusashi (Water jar for the tea ceremony, chrysanthemums, painting in overglaze enamels and gold) Chrysanthemums painted in enamel colours alternate with trellises rendered in gold fired directly on to the glazed white body.

（The National Museum of Modern Art, Tokyo）
Imaizumi Imaemon Iro-Nabeshima usuzumi sokamon hachi (Large bowl, Iro-Nabeshima type decoration of flowers on an ink-grey ground) The ink-grey ground that provides such an effective background to the enamel painting was achieved by the spraying on of an underglaze pigment.

（The National Museum of Modern Art, Tokyo）

Kinsai = Painting in overglaze gold whereby a solution containing powdered gold is applied to a glazed or enamelled surface and fused on in a further firing of between 530 and 600?, which is slightly lower than the temperature used for enamel colours. After firing the surface is polished to bring out the lustre of the gold. A form of liquid gold known as suikin is sometimes used in place of gold.
Kinrande = A method of decoration whereby gold foil rather than dissolved gold is applied to the ceramic surface. Although the gold leaf used is relatively thick, care must be taken to prevent the temperature rising to a level whereby the gold leaf will sink into the underlying glaze. Fixing of the gold leaf is sometimes done with urushi lacquer rather than by firing.
Saiyu = The application and firing on of coloured glaze to a previously high-fired porcelain body. When the whole surface is covered in glazes of different colours, they fuse together to create a delicate gradated effect.
Sansai = Sansai or three-coloured wares are characterized by the use of low-firing lead glazes containing copper, iron and other colourants. Historical prototypes exist in the form of Tang and Nara three-coloured wares (To-sansai and Nara-sansai). Green, yellow and blue are the usual colours, but depending on the work fewer or more colours may be employed.

Tokuda Yasokichi Yosaiko (Jar, porcelain with striated polychrome decoration) A colourful piece using glazes of different colours on a porcelain body. The glazes have melted into each other during firing to produce a delicate gradated effect.

（Private Collection）
Kato Takuo Sansaibachi "Soyo" (Bowl, "Blueness", three-coloured ware) A fine example of contemporary three-coloured ware using vibrantly coloured shades of low-firing light blue and green glazes.

（The National Museum of Modern Art, Tokyo）

Yurikinsai = A low temperature glaze of the same colour as the high-fired glaze is applied to the surface of the vessel and fired on in a further firing. Gold leaf is then applied and covered with another layer of glaze so that it is effectively sandwiched between two layers of glaze. Although this adds to the durability of the gold decoration, it is a highly specialized technique that requires much care to ensure that the gold leaf doesn't roll up or melt into the glaze during firing.

Imaizumi Imaemon XII Iro-Nabeshima ryokuji sarasamon hakkaku ozara (Large octagonal dish, Iro-Nabeshima type textile (sarasa) patterning against a green ground) The motifs have been rendered in the form of underglaze cobalt blue (gosu) outlining filled in with gradated colouring (dami). The surrounding areas have been painted in green enamel to give definition to the decorative scheme.

（The National Museum of Modern Art, Tokyo）
Sakaida Kakiemon XIII Iroe sokamon obachi (Large bowl, flowers and grasses painted in overglaze enamels) The expansive decoration of flowers and grasses has been executed in red, green, yellow and blue enamels on a milky white porcelain (nigoshide) ground.

（The National Museum of Modern Art, Tokyo）

Firing

The kilns used in Japan for firing ceramics were traditionally fuelled by firewood. In modern times oil and kerosene have been used, while nowadays electric and gas kilns are popular.
Ceramics are usually fired in saggers or stacked on kiln shelves.
Kilns are heated slowly so that evaporation of water from the clay body and the burning of organic materials take place without causing damage, every attempt being made to achieve evenness of temperature throughout the kiln. The colour of the finished product depends to a significant extent on whether oxidizing or reducing conditions are maintained when the clay vitrifies and the glaze materials turn to glass between 1000 and 1200?.
Oxidation firing involves the complete burning of the fuel. Reduction firing takes place when excess fuel is added to the kiln to such an extent that it draws chemically bound oxygen out of the clay and glaze materials.
Similar glazes, for example, containing small amounts or iron will turn yellow when oxidized (as in Kiseto (Yellow Seto) ware) and bluish green when reduced (as in pale blue porcelain).

Kaneshige Toyo Bizen obachi (Large bowl, Bizen ware) The hidasuki (lit. 'scarlet sash cord') effect particular to Bizen ware is well demonstrated on this piece. It was caused by the reaction of iron in the clay body with alkalis in the straw wrapped around the dish prior to firing.

（The National Museum of Modern Art, Tokyo）
Yamamoto Toshu Katatsuki chaire (Katatsuki type tea caddy) Ash falling on the tea caddy during firing has turned into a glaze with a distinctive naturalistic patterning.

（The National Museum of Modern Art, Tokyo）

Terminology

Ido = A variety of Korean tea bowl highly valued by tea masters.
Imari = General term for porcelain produced in Arita and its neighbouring region in Saga Prefecture. The name comes from the port of Imari, from which the porcelain was transported. Since the Meiji period the term Arita ware has been used with increasing frequency.
Udei = Black-firing unglazed stoneware also known as kokudei. The character ""u"" means crow, the reference being to the black of crow feathers. The terms udei and kokudei employed in connection with Tokoname and Banko wares are used in contrast to the term shudei or red clay.
Onihagi = A type of Hagi ware with a high proportion of coarse sand in the clay body.
Kaki-otoshi = A decorative technique that involves the use of a spatula to scrape off slip or glaze applied to a clay body.
Kakewake = The application of two of more glazes to different areas of the same vessel as seen in Oribe and other types of ware.
Kannyu = Crackling of the glaze caused by differences in rates of shrinkage of the clay body and the glaze.
Kinyo = Jun kilns, well known for having produced stonewares with a milky lavender-coloured glaze during the Northern Song, Jin and Yuan periods.
Gosu = Pigment used in sometsuke decoration whose main constituent is cobalt oxide. It turns dark blue when fired in reducing conditions.
Kohiki = Also known as kofuki, the term is used to describe ceramics with an iron-bearing clay body covered with white slip and an ash glaze. The term derives from the resemblance of the surface to sprinkled powder.
Suminagashi = A marbleising technique in which white slip and iron-rich slip are mixed together and applied to a clay body.
Tanka = A carbonisation technique in which the kiln is sealed after the addition of a large amount of soot-producing fuel such as pine needles so that the carbon impregnates the clay body. Also known as kusube-yaki.
Chaire = Tea caddy used for storing powdered tea. Tea caddies are among the most highly prized varieties of tea utensil. They have ivory lids and are kept in special textile bags known as shifuku.
Tenmoku = A type of tea bowl with a low foot, flaring sides and an S-shaped rim historically used in China for drinking tea. The name is derived from a mountain in Zhejiang Province in China. The term Tenmoku glaze is used generically for dark iron-bearing glazes similar to those used on Tenmoku tea bowls.
Nagashikake = Application by ladle of secondary glazes of different colours subsequent to the initial glazing of the whole vessel.
Hidasuki = Literally 'scarlet sash cord', a decorative technique that depends on the reaction during firing of iron in the clay body with alkalis in the straw wrapped around the unglazed vessel.
Mizusashi = Fresh-water jar used in the tea ceremony to store water for replenishing the cast iron kettle.