top of page

Development of wood-fired ceramic kilns in Japan

The different ceramic styles and types (pottery, stoneware, porcelain) have been profoundly influenced by the development of kilns. This development has had a major impact on the development and history of the individual ceramic workshops, not only from a technological point of view but also from an economic one. Therefore, before going into the history of the different styles and workshops, I would like to give some insight into the development of kilns in order to provide a better understanding of the economic aspects of this process, which have had a fundamental influence on the development of the styles, but which are less well understood.

To burn ceramics you first need heat, and to do that you need to burn something. To burn it, we need three things: oxygen, combustible material and heat, which ignites the combustible material. For the purposes of this article, wood will be the combustible material that will be important to us.

We cannot use just any kind of wood. Anyone who has tried to light a campfire knows that wet wood is very difficult. Also, I think many of us made the mistake of throwing too thick, large pieces of wood on our first fires, and they went out. What does it mean for ceramic kilns that you need a lot of dry wood for ceramic firing, which has to be chopped up and stored?

It means a lot of work and usually at least a roofed wood store. And if you don't want to transport a lot of wood to your kiln, it's worth building it in a wooded area. Since ceramics require clay and water, all these conditions combined reduce the number of areas suitable for building a kiln. But let's look at how kilns have evolved.


Pit kiln


This was the first chemosynthesis, which appeared in human history about 10 000 years ago. By this time, human cultures had reached a stage of development where they had settled down, grown crops and needed a way to store the produce. Pit furnaces were a solution to this need.

A pit kiln is technically nothing more than a shallow pit dug into the ground, in which straw and wood are placed, and objects made of clay are placed in between and even wood is placed on top, and then the pit is sealed with something, typically simply buried and left with enough openings to allow enough air to get in so that the wood and straw can burn. The filling in of the pit provided the insulation that was able to keep the heat in. In such pit furnaces, temperatures could rise to 550-650 °C. Therefore, the ceramics made in this way, while still porous, were relatively soft (for ceramics) and brittle. I wrote about this in more detail in my article Clay-ceramic-porcelain.

The other serious problem that has arisen with these kilns is that burning pieces of wood have often fallen on the pots and broken them. In addition, the temperature could not really be controlled, and heating ceramics too quickly could lead to the ceramics bursting. Therefore, many pots were damaged during the firing process and became unusable. You can see that this was not an efficient kiln, but it is still used by primitive peoples today. Its great advantage is that it is easy to make.





Beehive kiln


This was the next important step in the history of the development of the kiln, which appeared around 2000 BC. One of the important changes in these kilns was that the firebox was separated from the vessels to be fired, so that much less waste was produced. The other major advantage was that additional pieces of wood could be inserted into the firebox during firing, so that the heat could be raised and maintained for longer. In order to provide the fire with enough oxygen, a hole was initially cut in the top of the kiln where the hot air could escape and the resulting air movement drew fresh oxygen-rich air into the combustion chamber.

In order to control the air flow, a damper was placed on the smoke outlet. Kilns built in this way could reach temperatures as high as 1000°C, which allowed a much denser, harder ceramic to be produced that was also much more durable. However, these kilns had to be built and, as they were a kiln of considerable value, they had to be protected from the weather.

When a kiln gets wet, the clay and bricks that make up the kiln absorb water, which takes a lot of energy to evaporate and often causes the outer surface to be stripped by the water turning to steam. This reduces the thermal insulation layer, which reduces the efficiency of the kiln.



Climbing kiln (Dragon kiln)


This is a traditional Chinese ciln type, which is also used in Korea and Japan, as well as China. The increased demand for ceramic vessels may have played a major role in its development. These kilns were long, relatively narrow kilns built on the side of a hill or mountain because they required a 10° to 16° slope for the air to circulate properly. If you didn't want to build your own mountain, you had to find one.

These furnaces already had a chemist. Inside, the ceramics were placed on small terraces in a staggered arrangement, and additional fireboxes were created on the terraces, which could be fed with wood through openings carved into the sides of the kiln. This was necessary because a single combustion chamber could not heat a kiln of this size to the right temperature. Another advantage was that the heat from the lower furnaces fed the higher ones.

Some of these kilns were up to 60 metres long and could fire up to 25 000 pots at a time. By the early 12th century AD, they could be up to 135 metres long, according to some records, with a capacity of 100 000 pots. The great advantage of this type of kiln, in addition to its capacity, was that it could reach temperatures of up to 1400 °C, making it suitable for the production of stoneware and porcelain.



One of these kilns was already a huge asset, the cost of which no potter could afford. To build these kilns, to fill them with pottery and to heat them, it took a great deal of cooperation and a wealth of support. Huge quantities of wood were burnt in each firing, and the firing itself took a long time.

A similar but improved kiln still in operation today is operated by master ceramist Ken Matsuzaki in Japan. His kiln holds "only" 900 ceramics. It takes 7 days to heat his kiln and then at least that long, if not longer, for the kiln and the ceramics inside to cool down. A kiln like this takes a large team to heat up. The following film by Ken Matsuzaki: "Elemental" feature film about Japanese potter is worth a look. It is long, but gives an interesting insight into the workings of these kilns.

The long tubular shape of the crawl space meant that heat flowed quickly through it. The heat generated by burning a lot of wood reached the chimney very quickly and only heated the ceramics for a short time, as there were no obstacles in the kiln to prevent this. The next type of kiln was the answer to this problem.


Noborigama (Anagama) kiln


This type of kiln is an improved version of the climbing kiln, which developed in the 17th century. Like the climbing kiln, this kiln was built on the slopes of hills and mountains, but the kiln itself is divided into chambers, which are only opened at the bottom.

These also have a central firebox at the bottom of the kiln, but each chamber also has a firebox. The side of each chamber furthest from the firebox is only connected at the bottom to the next chamber and opens onto its firebox. Thus, the heat produced in the previous chambers already preheats the next chamber and its firebox, so the same heat is used several times. In addition, the individual chambers are designed either by building baffles in the middle or by positioning the clay pots so that they direct the flames and heat inside the chamber towards the ceiling of the chamber, thus describing a kind of wave motion throughout the furnace.



As it travels a greater distance it heats the ceramics more efficiently before the heat is removed through the chimney after the last chamber. In addition, the chambered layout allows you to control the heat even chamber by chamber. Typically, these kilns are heated up to 1300 degrees C°. In the largest Noborigama kilns, up to 100 000 ceramics are fired at a time and a single firing can last for weeks or even more than a month.


Summary and present


As you can see, these huge kilns are already of enormous value and represent a lot of work that no potter and his team could afford to do. Thus, if for some reason the patron of a kiln could no longer fund its operation, its maintenance and existence was threatened. This is what happened, for example, with the Sarayama kiln near Fukuchi city, but I will write about that in our next article.

Of course, the technology evolved and coal and then gas-fired furnaces and electric furnaces appeared. However, wood-fired kilns are still a tradition today. So much so that, as far as I know, there are large wood-fired kilns in Japan and China where potters can rent space to fire their creations under certain conditions.

One of the charms of wood-fired kilns is that in many places the ceramics are not glazed, but the ashes of the burnt wood are melted onto the ceramics as a natural glaze, creating very varied patterns that are only partly under the control of the master potters. So it is always a surprise to them what will emerge from the kiln.

According to the literature I've read, pottery masters have about 85% control over what happens in these kilns. This is also a huge risk, because if something goes very wrong during firing, it can ruin months of work. For this reason, ceramics made in this way can be of enormous value and can be very expensive.


Sources:

http://theantiquesalmanac.com/potteryintheancientworld.htm




205 views0 comments

Comments


bottom of page