Obvara Firing - 6 x 6 x 4
The obvara firing technique is a technique originally used to seal low fire pottery. It is believed to have originated in Eastern Europe during the Middle Ages. There is a revival of the process underway in Ukraine and the Baltics. It is nicknamed "Baltic Raku."
A solution which is often called a "brew" is a mixture of flour, yeast, and water.  It is mixed at least three days in advance of firing to allow the brew to ferment (just like soda bread starter). Pieces are made and bisqued before the final firing.
Using a raku kiln, pots are fired to 1650 degrees F.   Pieces are removed from the kiln one at time, dunked into the brew and then quickly into water. The surface of the pot is scalded by immediately placing the hot pot in the brew, leaving a wonderful variation of color from creamy tans, to browns and black, and sometimes speckled.  Then they air cool. The brew burns quickly on the surface of the piece before going into the water. The water stops the burning and color change.
 
The crackling effect is formed by brushing the surface of a thrown pot with sodium silicate, quick-drying the surface with a heat gun or blowtorch until the surface no longer is tacky, then expanding the form from inside.  The sodium silicate solution hardens on the outside and cracks are formed as you force the clay to move.