It is an ancient technique of firing by which a glowing vessel is removed from the kiln immediately after the glaze has reached the temperature of maturation at about 1700 F. to 1900 F. Most of the 'California” raku developed in the 1960s and 1970s contain a large amount of copper carbonate which give the myriad of colours that you see in this gallery, (alongside the white, black and grey pots of the Naked Raku)
Once the temperature is reached, the glowing red hot piece is moved onto a bed of wood shavings and shredded paper, which bursts into flame, then quickly covered with a metal can. The flame uses up all of the oxygen within the can, after which it draws the oxygen out of the glazes. The copper carbonate in the glazes transforms into the rainbow of colours that magically appear. Weather conditions and timing affect the results. Several loads on the same day may all have similar brightness and colouring as compared to another day. This process also turns the unglazed areas black.
After a short time, the can is lifted and the pot is immediately sprayed with water to 'freeze' the colours. Each one is totally unique and impossible to duplicate.
Pieces produced using this technique are porous and fragile. They do not hold water, are not food safe and should not be exposed to direct sunlight.
After being thrown, smoothed, trimmed and dried, the pot is given two coats of a fine clay slip called terra siglatta. Once this layer is dry, the pot is polished to give it the silky feel of the finished piece.
After the first firing, all the sections that are going to be solid black are masked off with tape.
Then one or several layers of slip (which won’t melt) are applied, followed by one or two coats of glaze (which could melt). While those layers are still damp, patterns can be drawn through to the bare clay underneath.
Once in the raku kiln, timing is very important as the glaze has to be heated just to the point where it almost completely melts. If it melts, it will penetrate the slip layer and fuse to the pot.
Once this point is reached, the pots are taken out. The thermal shock to the thin, hot glaze hitting the cooler air results in unique crackle patterns. Like glazed raku, weather conditions and the gods of random things all effect the results. The hot pots are put into burning materials, and covered with a metal tin. At this point, the smoke penetrates through the cracks in the slip and unglazed areas, turning those areas black, or grey.
After sitting under the tins for a while, they are taken out, and if you are lucky, the slip/glaze layer falls away like an eggshell. If not, you can be scrubbing for quite a while to get to the surface.
Regardless, the surface has to be gone over with a plastic rib to remove all the fine bits of slip that are always left, then finally they are warmed and waxed with beeswax polish.
Naked raku pots, like regular raku, are not watertight and will fade in direct sunlight.