This is a typical Japanese way of making pottery. Chawan tea bowls is the most common type, and given the way that it’s shaped, it’s less consistent with greater variation than is the case with thrown pottery.
Thrown pottery is the most common alternative way to make customized pottery, but Raku is rather hand-shaped. Contrary to porcelain, it’s water absorption rate is relatively high as a consequence of the firing temperature in the kiln. Traditionally covered in lead glazes to make the material less porous and allow it to serve as a tea cup.
Additionally, it’s also removed from the firing while still being extremely hot and taken outside to cool off.
If you look at its history, it was traditionally red clay that was used for the purpose, and it’s now the 15th generation producing Raku, and the way of making it has helped spread Japanese culture all over the world. In the 18th century, a manual that described the process led to a wider spread of the style, and it is now made by both professionals and amateurs throughout Japan.
This traditional Japanese way of making pottery did not stay in Japan, but started becoming increasingly popular in the West in the 50s, although it was still different in style. Where it differs from traditional pottery in the way it’s fired is that it is both heated and cooled very quickly when it is taken out of the kiln without the temperature first being lowered, and the way of firing also leaves the pottery with special colors and patterns.
There are 3 ways that it is usually cooled, and each will impact what it looks like – it can either be put in combustible material, which will cause it to smoke, it can simply be left out in the open air, or it can be dipped in water, causing instant cooling. The colors will be fixed by dipping it in water, as the chemical reactions are abruptly stopped by doing so. If it is put in combustible material, the color from the smoke will stain the pottery.
The colors can additionally be affected by affecting the availability of oxygen in the process.
It’s also common for the Western variation to not actually be hand built but thrown instead, and they’re also known for being colorful than is the case with the original Japanese way of making it. By placing different things on the pottery as it’s removed from the kiln, different effects can be created by putting things on the pottery as it is removed from the heat, with horse hair and feathers being the most common things potters use for it. With the pottery still being extremely warm, the added objects will leave interesting patterns on the pottery.
Electric or Gas Kilns
There are two different kilns traditionally used for the firing – the electric and the gas one, and the gas one is more difficult to control in terms of temperature. Propane or natural gas is what is used in the gas kiln, although those will heat more quickly.
The way in which it is built will also affect the firing, since temperature differences can be created inside the actual kiln, and this will create different colors.
Western Raku also traditionally uses other types of glaze than lead because of its damaging effects to people drinking from it, and other metals are usually used instead. It’s not uncommon for pottery to break as a consequence of the thermal shock, from being cooled off so quickly. The more times that pottery is fired, the higher the chance that it breaks from it because of the repeated thermal shocks.
Quartz, grog or kyanite added to the body are ways to strengthen the material, so it is less likely to break from the firing and cooling sessions.
The control of oxygen, which is called reduction firing, will affect the way that the pottery is colored by reducing the available amount of oxygen. When the pottery can’t get enough oxygen, it stops certain processes. Both combustible material can be used, or otherwise an aluminum container that limits the flow of air is common in the western style, which makes the effect of combustible material more significant, and since the fire from the combustible material will need oxygen, it will try to get it from the pottery instead.
Different Ways the Design Can Be Affected
There are certain things that can be changed up that will greatly affect the look of the pottery, and the potters will use these things to affect the look that comes out of it.
The horse hair is added immediately as the pottery leaves the kiln, and it burns and leave a line on the clay. This is done without having the glaze added to it, so that the color sticks to the body.
This is done to turn a section black after limiting the oxygen availability. A slip is added to the pottery, and it can crackle in the process. Where it crackles, the carbon will be soaked into the clay. The piece then cools down and the slip is removed.
Copper is added with the intentin that it doesn’t soak up much oxygen, and that means that it needs t be taken quickly from the kiln to the place where the reduction takes place, as it is exposed to oxygen on its way there. The result is a bunch of vibrant colors.
A clear base containing metallic particles is added to the pottery, with the metal providing the colors. Depending on the desired colors, either cobalt, iron or copper are used. As you can also see from this section on copper roofing, the material will produce either a green or red result. Once again, how long it actually takes to get the pottery to the reduction area, will affect the final result.
The Heating of the Kiln
Traditional pottery isn’t placed into a warm kiln to start off with but rather a cold one that is slowly brought up to the temperature that it needs, and the whole process usually takes 8 to 24 hours, although the Raku process is different. It is usually a preheated kiln that’s used for the purpose, and it only takes 20 minutes during a short firing cycle t get to the desired temperature. It can also take hours, if that is what the potter wants. Where the western tradition is to use a reduction chamber, traditional Raku is simply left, at which point it’s done.
What Can You Use the Pottery For?
The sad thing is that Raku typically isn’t very functional. To be more functional, it can be treated with a post-firing material, but the glaze is very fragile. If it breaks off into whatever you put in there, it’s very easy to end up eating it. Dry food is better to use than liquids, but it’s still not a type of pottery that is really meant for its function.
While it may be tempting to drink from such cups, you do not want to consume lead glaze either, since it’s a heavy metal.
Raku is something that can also be made into beautiful ceramic wall tile given its lack of contact with other things. Here’s a beautiful example of a wall tile that you can install at home. Check it out on Etsy.