The long way to finished Raku ceramics
Everywhere you read it, but how is it done, this ominous Japanese raku? We turn up the propane gas and bring the light of the flame into the silky black of the ceramic surface!
Raku is an old Japanese technique and means joy. Exactly this comes up when firing these unique pieces, because chance is the master builder. More about the history of the raku technique and the background can of course also be found here. In summer, it happens almost every weekend - the Raku kiln is running at full speed at Keamik-Kartell.de and we smoke our ceramics properly black, but let's start at the beginning!
The clay for Raku
For our Rakubrand we use a different tone for building than for normal operation. In order to achieve the highest possible contrast in black and white on the beautiful unique pieces, it is advisable to use a clay with a high kaolin content. Due to the brilliant white colouring of the kaolin, this tone is all in all brighter than other white tones and thus provides a high contrast to the black of the soot.
We put both hand-turned and self-made ceramics in the raku firing. Due to this great flexibility, however, we have a problem with the chamotte portion. We need as high a proportion of chamotte as possible to give the clay the necessary support. Here a proportion of 30% has proven to be sufficient and delivers reproducibly good results. Due to the chamotte, the ceramics survive the temperature drops of the raku technique more easily without damage. Unfortunately, chamotte is sharp-edged and is very painful in the palms of the hands when turned. What is the solution to this problem? Work fast, sounds banal but is the only thing that helps. It is highly recommended to practice turning on rotary clay until you have reached a quite passable level and only then to switch to the mentioned raku clay. The turning of a clay with a high content of chamotte is still a very exhausting (pun!) activity. Working with a sponge offers some protection and is an alternative that is easy on the hands and should be tried out. Some ceramists from Keramik-Kartell.de reported having tried it with (latex) gloves. But the disadvantage was that they tear very fast and in the end they were more annoying than useful.
Now that the ceramics have been lovingly crafted, they are finally reworked and go through meticulous quality control. At this point, ceramics that might not survive the Raku firing can still be sorted out. Also at Keramik-Kartell.de it is all about saving resources and the used, dried clay can be easily slurried and reused at this stage of production. At this point, last corrections and the final grinding are made before the ceramics are put into the biscuit firing kiln. This first firing takes place at approx. 900 °C and turns the clay into the ceramics. From now on they are no longer soluble in water, but they are not yet waterproof either. It should be mentioned here that the glazed Raku ceramics are not waterproof either. To sinter the clay, about 1200 °C are necessary. However, since the ceramics are taken out of the red-hot kiln at about 1000 °C, the silicate contained in the clay cannot crystallize out and leaves the pores open.
Glaze and does it have to be a Raku glaze?
Now follows the glazing of the ceramics for the raku firing. For this we use our unmistakable self-applied Raku glazes. Experience has shown that all low firing glazes are also suitable as Raku glazes. However, one should be aware that Raku is a reducing firing. This means that the cooling of the glaze takes place under oxygen exclusion! This is exactly the important point that can turn yellow glaze into orange. Furthermore, a rather slight craqueleč usually occurs. This is related to the surface tension of the glazes, because they are not made for Raku. Some guests who participate in our volumes are sometimes surprised by this. We on the other hand like it, as surprises are always nice and give the pieces that certain extra. The bisqued ceramics are now, if necessary, deburred with stand paper, especially on the mouth area of consumer ceramics such as cups.
Before glazing, the ceramics are wiped with a damp sponge to remove the dust. This is a small, but very important step towards an even glaze. The dust lying on the ceramics acts like flour on the dough to be rolled out; the rolling pin does not stick. But that is exactly what we want when glazing! So the dust has to come down and this is best done with a damp (not wet!) sponge. In general, dipping/pouring is preferable to brushing or spraying. For an even colour we stir the glaze completely. You can do this with a stick or a twisting sling. We have found, however, that the plastic of the bucket underneath is conductive and will eventually just go through. To avoid this and because it just works really well, we use a washing-up brush to stir the glazes. The bristles of the brush mix the glaze very well and homogenize it. Now that the Raku ceramics are glazed, they have to dry. As we have the time and space, the ceramics are glazed the day before and can dry overnight in peace. Alternatively you can do this in a kiln, but there we are back to the resource issue.
The Raku firing day!
On the day of firing, the Raku kiln is taken out of its chamber. Raku is best fired outdoors (because of the soot development) and since you don't want to walk far with the 1000 °C hot ceramics, it is best to be outdoors right away. For this purpose, our kiln has wheels and when it is outside, it is equipped with the dry unique pieces in laborious detail work. When it rains, an umbrella is essential, because no water should get into the kiln. The equipping is all about the golden section. With the Raku, as much as possible must go into the kiln, but not too much. If there is too little in the kiln, it is a waste of space. If there is too much in the kiln, the flame or heat cannot develop properly and the whole raku fire is lost. This is a matter of experience and for a start we would recommend Less is more and you should feel your way slowly - better than having to repeat the whole raku firing.
Now the kiln is loaded, the gas is turned on and you have to wait. This waiting time at the raku also has something meditative about it and good things take time. During this time you can catch up on breakfast, fill the tubs with organic material, moisten cloths or just watch the thermometer climbing. Don't worry, it only takes a little longer with the first fire of the day. If the slabs are already warm at the second fire, it will go much faster.
Raku firing is stopped when the thermometer reads around 1000 °C and the glaze has reached its maximum melting point. Experience has shown that thermometers are not very accurate and should rather be regarded as an indication. If you are not confident to judge the burr of the glaze, you can use firing cones. These melt out at a defined temperature and are surprisingly accurate. However, they are only to be used as a support, because these cones do not know whether the glaze on the Raku ceramics has melted out. In the worst case, one puts the ceramics into the kiln again. We generally advise against more than two glaze firings, as the ceramics get grumpy and tend to react unpredictably in the kiln if you put them into the glaze firing a third time. We at Keramik-Kartell.de only use lead-free glazes. Due to our zirconium silicate sealing of the glazes, our colours are generally unmarked and therefore suitable for food.
Before taking the Raku ceramics out of the kiln, the protective clothing must be put on. This includes long-sleeved, non-flammable clothing. Leather, tough cotton (jeans) or a thermostable synthetic fibre such as Nomex is best suited for this purpose. Next, the face visor, breathing mask and a cap are put on. Do not joke about the fumes that develop! Finally, we work with metals and oxides on the Raku ceramics. If necessary, the organic materials smoulder and the heat eats eyebrows and eyelashes of equal size. Once you have put on your personal protective equipment, carefully remove one piece at a time from the kiln. The tongs used for this are not barbecue tongs from Sunday barbecues. The tongs are a good 1 m long and weigh approx. 5 kg, large appliances with nasty teeth. Here the clay is mentioned again. The tongs are coarse equipment and the force you apply is relatively difficult to dose. So you have to build stable and not turn too thin. As a rule of thumb you can remember a centimeter. When building, the Raku ceramics should not be thicker than one centimeter, but also not thinner. If you build thinner, it can happen that you "bite through" the ceramics with the teeth of the pliers while lifting them out of the kiln. If you build thicker, the weight of the raku ceramics is too high and you can handle it worse. In general, you should keep the weight in mind during the production.
The Raku ceramics are placed directly from the kiln into tubs with combustible, organic material. There is no specification or gold standard here. Rather, it is a question of preference and availability, taking into account health aspects. Suitable materials are dry leaves, sawdust, paper or newspaper or magazines. It should be mentioned in passing that printer's ink is harmful to health. We at Keramik-Kartell.de only use sawdust that is PESC-certified and untreated.
Now Raku is born! It's all about smoking, tasting and firing. Rule one is here again occupational safety. The ceramics ignite the shavings immediately and a small fire develops around the beautiful unique pieces. Here it is important to keep calm. The ceramics can easily burn for five minutes in the sawdust. They are sprinkled and turned over again and again. Only by turning them over can a uniform black soot be created as a contrast to the white tone. In the following, the tubs or pots are closed and covered with damp to wet cloths. Now the relaxation and meditation begins again. The Raku ceramics can now stew and cool down in the vessels for about 30 minutes. You should use this time to fill bowls with clear water. These are needed for the following scrubbing of the Raku ceramics. After the cooling time has expired, the still hot raku ceramics are taken out of the bowls and put aside to cool down - this can easily take another 30 minutes!
Raku scrubbing is like opening presents!
Scrubbing the ceramics is the final part of raku firing and is both tedious and beautiful. It is annoying to get the residues off the surface of the glaze, but to see the beauty... We have found that with soaped steel wool it is easiest to get the soot off the ceramics. Here you don't have to be afraid of scratching the glaze. It's always frightening how hard sawdust can burn into glass. Only muscle power and perseverance can help. The Raku ceramics are thoroughly scrubbed in clean water and finally rinsed again with clear water. This meticulousness is worthwhile, because when the many small black marks are gone, the contrast of silky matt black and shiny white can work much better. Now all the beauty of the handmade unique pieces is revealed and you understand why Raku means joy. It is always like unwrapping presents and you just can't get enough of the black cracks in the glaze. The Craqueleč makes each piece individual and unmistakably unique.
Raku is born out of fire and you can smell the ceramics and yourself for a while. But after a few weeks the smell of the ceramics has disappeared and it starts to tingle in your fingers again after the next raku firing!
