The origins of the word Celadon are much disputed but these days it is commonly accepted as a green cracked glaze made from wood ash and clay. In Thailand various types of wood are used according to the desired colour. The ash is usually mixed with silt from a rice field. The distinctive green colour of Celadon is due to the iron content of the glaze and the clay body. Other colours can be produced by addition of small amounts of metal oxides to the glaze.
Cobalt produces blue for example.
The glaze should be brilliant and evenly crackled. If the glaze is dull, as many antique pieces are, then the Kiln failed to reach 1260 degrees Celsius. The attractive crackle is caused because the glaze shrinks more than the clay body on cooling. During the 17th century the technique for producing Celadon and other fine stone wares was lost as a result of various wars and mass movements of populations. It was only in the 1950 s that several people began to try to revive the art .