is an abbreviation of the Japanese term raku-yaki 楽焼 is the result of an enamelling technique, in Japanese ceramics, developed in the sixteenth century. It is essentially related to the making of bowls for the tea ceremony.
consists of removing the molten pieces from the kiln, which creates a violent thermal shock. The enamel cracks. It is then smoked in a closed container to cut off the oxygen supply, causing the smoke to enter the cracks and blacken them.
This technique comes from Estern Europe and consits in dipping the piece in a mixture of fermented flour and water. (see video)