Celadon glazes have been made in Asia for centuries. The light green colour is produced by a very small quantity of iron in the glaze and clay when the kiln is fired with a reducing atmosphere. This reduction occurs when smoke present when the glaze is melting between 1100 and the top temperature1300 degrees centigrade).
My Celadon is a simple one typical of those made in China and Southeast Asia. This family of Celadons can vary between the green shown in the picture, grey, tan, and grey/blue, depending on the particular combination of clay and glaze materials as well as the firing pattern.