The raku pottery technique has it's origins in Japan. Raku potters were producing wares expressively for the Japanese tea ceremony. Raku,meaning "pleasure" or "enjoyment", was not introduced to the western world until the first half of the 20th century.
Raku is a process of taking pots, while they are still glowing red from the kiln, and placing them immediately into containers filled with combustible materials such as sawdust, dried leaves, newspaper, etc. A reduction or carbonization process begins once the red hot pots ignite the combustible materials. Lids are then put on the containers to create a totally smoke filled atmosphere. The result is that any unglazed areas on the pots will absorb and turn black from the smoke. During this extreme temperature change of cooling down, crazing or cracking occurs on many of the glazed areas on the pots. During the burning and reduction phase, the heat is so intense that the glaze surface becomes tarnished with soot. The final phase of the raku process is the cleaning. Cleaners, toothbrushes, and scouring pads have to be used to scrub clean, all glazed areas. Only at this time can you appreciate the end result.
Short video of Bill Herb during the raku process. (Grandson watching!)