The ceramic or Yakimono
There are several types of ceramic which can be classified into large categories.
Earthenware or Raku yaki
Earthenware is a composition of clay, often blended clays, which once baked became hard depending on the intensity of the fire. Earthenware, has been made following virtually the same techniques since ancient times; only in the modern era has mass production brought changes in materials and methods.
After the invention of glazing, earthenwares were coated with glaze to render them waterproof, sometimes glaze was applied decoratively. It was found that, when fired at great heat, the clay body became nonporous. This type of pottery, called stoneware, is preferred for domestic use.
Faience or half porcelain
It is called Toki or han jiki it is made of kaolin clay which once glazed at lower temperature become hard. The color is not so white compared to porcelain but is also glassy and smooth.
In general Japanese do not care so much about having thin porcelain like we do in Europe, it is why most of the production of ceramic in Japan can rather be classified as half porcelain, the shape, color and general appeal given by the piece is the most important character.
Porcelain, Jiki in Japanese, is a Chinese invention, it is made by firing a pure clay called kaolin, which once glazed at high temperature (1400 degree) become very hard, white, translucent and very glassy and smooth. It is mainly characterized by its hardness, ringing sound when struck, translucence, and shining finish. Kutani ceramics are generally not classified in this category.
This porcelain was called in the West china clay or Bone china. It is made of 5% bone ash and china clay, it was made in the West in imitation of Chinese porcelain
The Kutani technique
The process used to manufacture Kutani ceramic can be separated in 3 main steps. The first one consists in preparing the clay to be used to shape the pottery. The quality of the stone used as a raw material has the biggest importance for the final quality of the pottery.
The pottery is formed using potter wheel and will dry for a while before being fired for 8 hours at 800 degree. This product is then often referred to as a biscuit. This is the basic step common to all pottery type all over the world and since centuries.
The next and most important step is more specific to Kutani ceramic or generally to all type of porcelain production. A drawing is first outlined on the biscuit with cobalt pigment called ‘Gosu’ then covered with a sort of glass frit named glaze. Glaze is a liquid paste made of feldspar rock powder mixed with ash (wood, straw, rice hull..). After firing this past turns into a sort of glass. This operation called underglaze painting or some-tsuke has been firstly developed in China then imported to Japan and is very famous. The cobalt pigment turns into a deep blue color. Very few Kutani kiln have produced in the past sometsuke except Wakasugi kiln. Today Suda Seika and Juraku kilns in Yamashiro are quite famous for their some-tsuke productions. In addition to the outlines drawn with Gosu it is common to enamel the surface or part of the surface before firing. This whole process is called underglaze painting.
This operation is the most difficult of this process as it required a firing temperature of 1300 degree for 15 hours. The temperature must be stable and at the right value, therefore we can easily understand that with today modern technology, with gas or electric kiln and computer control there are no difficulties at all but in the past with wood and temperature control by the color of the flame it was an other story. That was one of the main problem encountered by the potter of the old Kutani kilns and this explain the difference of color of the porcelain which can go from a clear almost translucide white to a thick gray or yellow body. Of course the origin of the clay had also influence on the color of the semi finished product such as the clay material used by Ono and Wakasugi kilns which had a lot of alumni and turned yellow after firing.
There is also a possibility of just glazing the biscuit without any underglaze painting. That was the simple process followed by many kilns which produced just white pottery to be painted somewhere else by specialized kilns called nishiki kilns which were flourishing in Kanazawa area at beginning of the century.
After glazing begin the painting process which can cover several steps. In the traditional Kutani style 5 colors only are used, purple, dark green, red, yellow and deep blue. There might be several painting steps and between each one a firing between 800 and 1000 degree is necessary. This operation is called overglaze painting or Uwae-stuke or more generally Iroestuke. The last step is kept for the gold and silver painting which requires a final firing at 400 degree.
The production technique
The ceramic are produced in kilns, the first point to be considered before the establishment of a kiln was the supply of material suitable for making pottery, that is to say clay and wood. Clay is made of Kaolin which is found in granite area, therefore at the bottom of mountains. Then many kilns have been established in the past closed to mountain side, one of the key factor being also the presence of forest as the quantity of wood required to feed a kiln was tremendous. This is a raison why kilns were often close by each other as it was meaningless to transport wood or clay on a long distance. This also explains that sometimes kilns had to be closed down as wood had run out of supply.
Regarding kilns, we have to consider the so called Hon-gama which is used for overglaze firing and which allows to reach a temperature of around 1300 degree. There are several types of kilns which have been used since the old days. The most simple is a one room kiln it has a small entrance where the fire was made and a chimney for exhausting fumes. But this type of kiln by its design is very much wood consuming. However modern technique and the use of electricity or gaz have changed the situation and today most of the kilns are of this type.
The second type of kiln was developed to reduce the quantity of wood consumed. This kiln called Nobori gama is a succession of rooms built on a hill. The rooms, up to 10 or 12 are fired one after the other and the hot smoke exhausting from the first room will heat up the second room and so on. This technique imported from Korea was very much developed and almost all old Kutani kilns used it.
However today almost nobody use Nobori kiln specially with wood except one kiln still trying to maintain the old style, it is Suda Seika kiln in Yamashiro.
It is very clear that with an electric kiln 100 percent of the production will be good, temperature is homogeneous and stable, with a wood heated kiln an important part of the production will have defects due to these problems of temperature and stability without considering the difficulties for the persons who had to feed non stop the kiln during 1 or 2 days.
This is why maybe pieces made by such a type of kiln are more beautiful are not so regular and can express something you can not get from an electric kiln.
The last type is called Nishiki gama by opposition to the Hon gama which is described above and is solely used for high temperature firing. The Nishiki gama is a small size kiln used by painters for overglaze painting and which allows to reach 800 degree. Very often this kiln was settled inside private housing. This type of kilns developed a lot at the beginning of the century specially in Kanazawa area where many painters were working. The first electric kilns have been introduced around 1920, today all of them are electric.
I like to come back to the question of the wood. I said above that 1 or 2 days were required but this is when considering a 2 rooms Nobori kiln, so it is easy to imagine then the time and quantity of wood required to feed the old Kutani kilns which had 12 rooms, we are now talking of weeks. Furthermore to make things more difficult, one can not use any type of wood in order to reach the 1300 degree, but only a special kind of pine tree called Akamatsu had to be burned.