Euan Craig

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Glazed Expression

Euan Craig

TRADITIONAL MASHIKO GLAZES

For all that Mashiko has a mere one hundred and fifty year history as a pottery centre, it has had a significant impact on international ceramics and what has now become the mingei tradition. Primarily due to the efforts of Shoji Hamada, Bernard Leach, Soetsu Yanagi and other members of the Mingei Art Movement, the beauty inherent in traditional crafts became an aesthetic benchmark for many modern artists. Hamada chose to live and work here in Mashiko because of its tradition of simple domestic pottery, and his activities overseas made Mashiko famous internationally. He also opened the door for many foreign students of ceramics to come and study here, making Mashiko one of the most accessible traditional Japanese pottery centres for the international community.

Mashiko became a centre for pottery manufacture for both geographical and geological reasons. The physical problem of transport during the nineteenth century dictated that pottery was generally produced close to where the clay was found. A potter who had moved to Mashiko when he married a local girl discovered good clay while working in the rice paddies, and began making pottery in the winter months. There were hills on which to build climbing kilns, and forests of red pine with which to fire them.

A local stone, Ashinuma stone, was used for building here, and when used to cover the kiln fire mouth the hot surface melted. It was discovered that when this stone was crushed to a powder and applied to the pots, it formed a well fitting, durable and attractive glaze. Its colour and surface were reminiscent of the seeds of persimmon fruit, a so it became known as “Kaki” glaze. Mashiko clay was not suited to Anagama style natural glazing. It needs to be thrown fairly thick and doesn’t vitrify well, tending to remain porous, so the unctuous and non-crazing “Kaki” glaze became the trademark of “Mashiko Yaki”. Noborigama climbing kilns were the safest most reliable and cost effective firing method and became the standard in Mashiko. The front fire box contained no pottery, its purpose was to heat the rest of the kiln without the flame directly hitting the work itself until safe temperatures had been reached. Most firings were oxidation and thousands of pots could be fired in each kiln, safely, reliably and of standard quality.  

Other local minerals were also discovered to be useful in the making of ceramics. In the fifteenth year of the Meiji era (circa 1882) “Terayama” clay was found, a fine white high silica clay good for engobe decoration or in glazes. “Ohyatsu” sand and “Shinpukuji” primary clay were added to the list, as were other readily available materials. Being a rice farming community, rice straw and rice husks could be burned in large quantities, the ash used for glazes. Pine ash from the kilns, and hardwood ash from charcoal braziers all became part of the palette. Accessibility and cost were the main criteria, and from those materials developed the distinctive range of Mashiko glazes.

The other geographical advantage that Mashiko had was its proximity to Tokyo, the capital of Japan, and the market that it represented. Mashiko is only one hundred kilometers north of Tokyo, and close to the “Kinugawa” river. The finished pottery could be easily transported to the river port at “Mohka”, then carried by boat to Tokyo for sale. Mashiko was ideally situated, with plentiful materials and an accessible customer base, and so it thrived and grew as a pottery production centre.

When Hamada came here in the 1920’s, Mashiko was still a rural village, and coupled with its pottery tradition, he felt it was the perfect place for him to settle. Part of the Mingei philosophy was a healthy, “close to nature” lifestyle, and so Hamada established his pottery as a “Han no, Han yo” (Half Agriculture, Half Pottery) workshop. The beautiful gardens that are now part of the HamadaMuseum were once vegetable beds with chickens scratching among the leeks. Already skills had begun to be speciallised, and there were several clay makers. In hard times they would often take dray loads of clay up to the Hamada compound unexpectedly, knowing Hamadas generous nature. “Here’s your clay.” They would say. “Oh,” he’d reply, “Just take it round the back”. As a result, his grandson has seventy years worth of clay stockpiled.

In the early days most of the potteries processed their own glaze materials, washing the ash, calcining and crushing the Ashinuma stone, and some potteries in Mashiko still do today. Terayama clay had to be left out in the weather for six to twelve months to allow the sulfide contained in it to be naturally washed away by the elements. The mixing of glazes was done by liquid volume, not dry weight as is generally done in the west. Materials were slaked, decanted, sieved and mixed into slurry. When these liquid glaze materials were all the same specific gravity, the thickness tested by experience rather than hydrometers or pint weight, they were blended together by ladle. Four ladles of Kaki, three of Kamado feldspar, two of Pine ash and so on. The prepared glazes were then applied to broken shards of bisque ware, allowed to dry, then scratched through with a fingernail to check application thickness. Bisque firing temperatures were very low, 700-750 centigrade perhaps, so as not to waste wood, and as a result the pots were quite brittle and porous. The fly ash from the firing would be dusted off, then each pot wiped with a damp sponge immediately prior to glazing. This served the dual purpose of removing any remaining dust or ash on the pots, reducing the possibility of crawling, and expelling some of the air from the porous clay thus eliminating pinholing caused by bubbles escaping through the wet glaze.

 

There are six standard traditional glazes in Mashiko.  

 

KAKI

As I have mentioned, this glaze is made from a single material, Ashinuma stone. It is effectively an Iron Rust glaze, the naturally occurring iron oxide in the glaze chrystallizing on the surface to give it the distinctive red colour.

 

Unity Formula

0.34 KNaO                0.82 Al2O3                              6.57 SiO2

0.28 CaO                   0.24 Fe2O3                

0.38 MgO                   

 

KURO

“Kuro” means black. Using Kaki as the base glaze other materials are added to “water it down”, reducing the total iron content to a point where it no longer migrates to the glaze surface. This particular recipe contains some Cobalt to increase the density of the black.

 

Recipe by weight of dry materials;

Wood Ash (Do bai)

7.2

Rice Husk Ash (Momi bai)

2.2

Rice Straw Ash (Wara bai)

5.2

Terayama clay

2.9

Kamado Feldspar

7.4

Ohyatsu Sand

16.2

Lime Stone

4.4

Ashinuma Stone

54.5

Iron Oxide

1.3

Cobalt Oxide

0.07

 

Unity Formula

0.26 KNaO                0.54 Al2O3                              4.93 SiO2

0.60 CaO                   0.12 Fe2O3                

0.14 MgO

 

Iron Oxide                1.30%

Cobalt Oxide              0.07%

 

 

NAMIJIRO

This glaze translates as “Standard White” glaze. It is a simple, reliable semi transparent feldspathic glaze.

 

Recipe by weight of dry materials;

 

Unity Formula

0.23 KNaO                0.45 Al2O3                  4.07 SiO2

0.76 CaO

0.01 MgO

 

 

Ohyatsu Sand

58

Limestone

18

Terayama Clay

13

Kamado Feldspar

11

AME

“Ame” means “candy”, and this glaze derives its name from its transparent toffee colour and glossy surface. It is made with the simple addition of ten percent of manganese oxide to the “Namijiro” base glaze.

 

 

NUKAJIRO

“Nuka” is rice bran, but this ash glaze actually contains the husk and straw ash left from the rice harvest. “Jiro” or “Shiro” means white, and this is a milky white glaze which can be almost opalescent.

 

Recipe by weight of dry materials;

 

Wood Ash

34

Rice Husk Ash

25

Rice Straw Ash

5

Terayama Clay

13

Kamado Feldspar

23

Unity Formula

0.15 KNaO                0.29 Al2O3                              3.46 SiO2

0.75 CaO

0.10 MgO

 

 

NUKASEIJI

“Seiji” is the Japanese term for Celadon glazes. In the west we use Celadon to describe a family of Iron blue or green stoneware glazes, but “Seiji” simply describes the colour. This glaze uses “Nukajiro” as the base glaze, with the addition of three to four percent of Copper Oxide.

 

Over the years specialisation continued and the Mashiko pottery cooperative (Mashiko togei kyodo kumiai) came into being, processing and providing clay and materials to the community of potters. People came from other parts of Japan and the world to study and work here, and many of them stayed. Now there are at least 400 potteries in the Mashiko area. Two major clay and material suppliers service the needs of the potters, with virtually any type of clay or mineral from anywhere in Japan available. Transport is no longer a limitation, and the reliance on local materials has gone. It has been replaced by a huge range of glazes, styles and quality, making variety itself the specialty of Mashiko Yaki. 


The traditional materials, like Ashinuma stone (the powdered form refered to as “Aka ko” or “Red powder”) or Terayama clay, have been virtually mined out of the accessible deposits. They are only available to members of the cooperative now. Deposits still exist, but they are on private land or under peoples houses. The quality of the clay has changed, and clays and minerals from other regions, even other countries, are being blended with local clays to approximate the traditional clays. Replacement materials are available. With chemical analyses of the original materials glazes of similar quality and colour can be achieved. David and Margaret Frith from the UK for example produced a Kaki glaze with other materials that, when exhibited in Mashiko, the local experts 
couldn’t differentiate from the original, except to compliment them on their excellence. 


What we consider traditional Mashiko glazes are now the domain of the global pottery community. What were considered glazes and styles of other regions are now part of the Mashiko vocabulary. A hundred and fifty years ago Mashiko pottery was just a fledgling. When Kaki was discovered it was an innovation. Eighty years ago Mingei was revolutionary. At what point they became tradition I am not sure. The second generation, the third? Is the mere repetition of a process or the continued use of a material tradition? I do not believe that tradition is about regurgitating the work of past masters. Tradition is a vehicle which teaches each successive generation the cumulative knowledge and wisdom of all those who preceded them. I have no quarrel with tradition, it gives us a foundation upon which to build. It should not be a structure that restricts us, but a stairway that leads us to new discoveries. 


There have never been secrets here in Mashiko, but every pottery had its own variations on the standard glazes, their application or firing. Changes in lifestyle, the needs and desires of the market, coupled with access to new materials and technology have made Mashiko a place where any style of pottery is acceptable. It is up to the individual to find their own form of expression.   

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