Raku generally refers to a type of low-firing process that was inspired by traditional Japanese raku firing. Western-style raku usually involves removing pottery from the kiln while at bright red heat and placing it into containers with combustible materials. Once the materials ignite, the containers are closed. This produces an intense reduction atmosphere which affects the colors in glazes and clay bodies. The drastic thermal shock also produces cracking—known as crackling since it is deliberate. The original Japanese style of raku is an outgrowth from Buddhist influences in life and especially in the tea ceremony.
Delving further into raku's history, it dates right back to the early 1550s as mentioned specifically for the Zen Buddhist Masters in their ceremonial teaware. It's been well documented that this was the favored method of ceramics for the Zen Buddhist masters as raku ware touches on many of the things that Zen philosophy embodies, most notably its simplicity and naturalness.
Raku firing really is one of the most natural techniques that you can encounter in pottery. In raku firing, all of nature's elements are used, earth, fire, air, and water. The earth is used to make the pot, then it's put into a reduction chamber kiln, then plunged into water. The cold water halts the firing process. A lovely fact about raku is that its name literally translates as 'happiness in the accident'.
Types of Clay
Any type of clay can be used for a raku firing, although specific raku clay can be bought and this creates the best results. Raku clay has typically high thermal shock resistance and low shrinkage. Another important factor in the creation of your raku firing is choosing the right type of glaze, a glaze whose properties react in the best way in a raku firing.
Most importantly, raku is a low fire kiln process, which means that almost any low-fire glazes, whether you have bought them commercially or created them yourself, should work just fine. The temperature of a raku firing reaches around a cone 010 - 06 range.
Despite raku's history and the fact it used to be used in ancient tea ceremonies, it's recommended that you keep your raku pieces purely decorative. This is due largely in part to the fact that it's fired rapidly, meaning, although it's beautiful it can be porous, fragile and sometimes the glaze might flake in places. So while the pieces can look incredible, they're not really to be used as functional ware.
There is a range of raku kilns on offer that are designed specifically for the raku firing process and experienced potters can also make their own raku kilns in a dustbin. A raku firing is usually done after the piece has been bisque fired first. Then the glaze is applied and it's put through a raku firing. The firing cycle of raku is usually much faster than a typical firing and if you're plunging your raku ware into the flames, a firing can take as little as 15 - 20 minutes to fire. In raku firing, you must put your ceramic ware into combustible material for example sawdust. Be prepared, with raku firing a huge amount of smoke is created.
You'll take your raku ware out of the kiln when it's red hot, so you won't be able to see the result until the piece has cooled. Some of the interesting results you might see are crackled glaze surfaces, black smoked unglazed clay or even beautiful metallic effects. If you like this kind of effect you can also look into saggar firing or obvara firing.