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Raku, the technique

This technique was discovered in Korea and then developed in Japan in the middle of the 16th century.

The raku word comes from an ideogram engraved on a golden seal which was offered in 1598 to the Korean Chojiro by Taiko, master servant at the ceremony of the tea. The implication of the potter in the raku often echoes his philosophy, his roots and his cultural sense.

The technique of raku is in fact a way of cooking. The incandescent parts are taken out of the oven, and can then be smoked, dipped into water, or left at free air. They undergo an important thermal shock and, in every case, express under these constraints the story of the ground, the fire and the water.

The multitude of the involved parameters allows obtaining results varying in the infinity, what confers to the manually realized parts, the quality of unique object. Before applying the technique of the raku to potteries, parts are modeled in terra-cotta, thrown with a wheel or made according to any other technique used in the world of the ceramic.

We generally use a ground which is stoneware, better resisting to the sudden temperature variations. By taking some precautions, we can also use earthenware. Parts are first cooked in a traditional oven (electric for example) at nearly 1000° C to harden them and to obtain what we call the biscuit. This biscuit has to be solid enough, but still remains porous to fix the enamel, which is also call glaze.

The used glazes are said "low temperature", because the 2nd cooking is done at temperature range generally situated between 960 and 980°C, in an oven working with gas, wood or fuel oil. These types of ovens allow obtaining a cooking in reducing atmosphere, contrary to the electric oven which works mainly in oxidizing atmosphere. Glazes can be applied by soaking the parts, or with a brush or a pistol, depending on the requested effect.

Once parts are glazed, they are cooked a second time. They can be put in the cold oven, but often the oven is preheated and the enfournement is made hot. The cooking is led to a fast rhythm, and the final temperature is achieved within a short cycle of nearly one hour. Sometimes the cooking can last several hours according to the size of parts and their requirements.

The enameled parts are taken out of the oven when the temperature inside it reaches approximately 1000 °C. They are then left for a more or less long time at free air to crack, and\or are quickly put on a bed of inflammable materials like sawdust mixed with paper. When the fire has started, the container is covered to stop the flame. The thick smoke which is generated then transforms the enamel in a random way.

This phase is the reaction of oxydo-reduction during which appear more or less silvered colors, crackles as well as smoke effects on the parts, specific to this type of ceramic.

After cooling down, parts are cleaned with an abrasive sponge, or steel wool to remove all the residues of soot and ash.

Ovens for raku are generally small and high-powered. They generally have a burner at the bottom and a simple blowhole on the top.

The type of cooking (oxidizing or reducing) can be adjusted by recovering more or less the blowhole with a piece of refractory plate.

Parts can also be cooked in a less conventional oven, like a simple hole or a pit in the ground.