Between the 10th and 14th centuries, potters of the kingdom of Goryeo developed a blue-green glazed ceramic (청자) whose formula, firing temperature, and control of the reducing atmosphere produced the translucent jade color called bise (비색), considered by contemporary Chinese of the Song dynasty to be the most beautiful in the world. The technique involves a feldspathic glaze with traces of iron and titanium fired at approximately 1,250°C in a reducing atmosphere controlled with extreme precision. Goryeo celadon also incorporates the sanggam (象嵌) inlay technique, unique in the world, which fills incisions with white or black clay before glazing, creating bicolor patterns beneath the glaze. The exact formula for the bise color was lost with the Mongol invasions of the 13th century and was not reproduced in a laboratory until the 20th century. The historical canon presents celadon as a refinement of the Chinese tradition, ignoring that Goryeo celadon technically surpasses its Song equivalents in chromatic precision.