Yunomi (tea bowl) with impressed marks

Soda fired tea bowl with impressed marks. Porcelain slip surface with "orange peel" and red flame flashing; shino glaze inside.
Vapour fired to 1300C.
 
Soda, or vapour, firing is a firing process where sodium in some form - sodium carbonate or bicarbonate, is introduced into the kiln as a solution when the temperature is at 1250˚C. The soda immediately volatises, and combines with the silica in the clay to form a lustrous glaze with often spectacular surfaces where the flame has licked around the pot, taking the soda with it. The randomness of this process gives each pot its own unique character. Prior to firing, the pots are dipped into different clay slips (liquid clay) to give different colours and effects.