Process Salt glaze pottery

pouring salt wood-fired kiln, using carved-out piece of bamboo filled salt soaked in water.

the salt glaze formed on unglazed body reaction of common salt clay body constituents, particularly silica, toward end of firing. body should ideally richer in silica normal stoneware, , iron impurities can produce salt glazes. reduction atmosphere can employed reduced iron silicates powerful fluxes.

the salting mixture of sodium chloride , water introduced kiln when appropriate temperature reached, typically around 900 °c. kiln reaches higher temperatures, typically 1100–1200 °c, sodium chloride vaporizes , reacts steam form hydrogen chloride , soda. these vapors react silica in body , other body constituents. glaze of high alumina content (0.6 molecular parts) , relatively low silica content (2.6 molecular parts), , in main base soda, formed. salt glazes have been improved addition of borax, , sodium nitrate, salting mixture. colouring oxides can incorporated in salting mixture give decorative effects, such kind of aventurine glaze.

salt fumes in firing atmosphere react in following way:

2nacl + 2h2o → 2naoh + 2hcl


2naoh → na2o + h2o

in soda firings reaction little more direct, not requiring presence of water vapor:

na2co3 → na2o + co2

both hydrogen chloride , carbon dioxide gases; not react sodium oxide binds silica , other components of clay body. hydrogen chloride leaving kiln form hydrochloric acid vapour on contact moisture in air or kiln exhaust gases. remaining sodium oxide form salt reacting hydrochloric acid vapour gases exit kiln. sodium oxide (na2o) reacts alumina , silica in clay body form sodium alumino-silicate glaze. general reaction shown below, values x , y varying dependent on amounts of sodium oxide, alumina , silica composing glaze:

na2o + sio2 + al2o3·(sio2)2 → (na2o)x·al2o3·(sio2)y

salt can used decorative element on selected individual pots. biscuit ware can soaked in brine solution create salted patterns. rope , other textiles can soaked in brine , wrapped around biscuit ware. salt can added, in solution, coloured clay slips , can sprinkled onto biscuit ware in protective, ceramic containers called saggars. related technique, soda firing, substitutes soda ash , / or sodium bicarbonate common salt. whilst application method little different, alternatives need sprayed kiln, results similar salt glazing subtle differences in texture , colour.