What is the green color made of in these Goryeo Dynasty stoneware pieces?
This glazing technique you see here is known as celadon and Korean potters have long been known for achieving jade-like colors.
The color is achieved through chemical reactions between iron in the clay, and iron oxide, manganese oxide, and quartz in the glaze when they are placed into a reduction kiln that removes oxygen during the firing process.
What is celadon?
Celadon is a blue-green glaze, often used on stoneware, a kind of ceramic. Celadons are named due to the greenish-blue color of their glaze. Their color can vary in tone from grayish to greenish depending on the composition of the clay. The color of celadon is achieved by placing a green-colored glaze over a gray clay body and the reaction of iron oxide when the vessel is fired in a reduction atmosphere.