The anagama kiln is an ancient type of pottery kiln brought to Japan from China via Korea in the 5th century.
The anagama is fueled with firewood, in contrast to the electric or gas-fueled kilns. A continuous supply of fuel is needed for firing, as wood thrown into the hot kiln is consumed very rapidly. Stoking occurs round the clock for about 5 days until a variety of variables are achieved including the way the molten pots look inside the kiln, the temperatures reached and sustained, the amount of ash applied, the wetness of the walls and the pots, etc.
Burning wood not only produces heat of up to 1400°C (2,500 °F), it also produces fly ash and volatile salts. Wood ash settles on the pieces during the firing, and the complex interaction between flame, ash, and the minerals of the clay body forms a natural ash glaze.