Discussion of ceramic materials and techniques indigenous to the Koreans. Koryo potters were the first in the Far East to experiment with an underglaze of copper oxide decoration, which (being volatile) was apt to turn grey, brown or black, but when fired successfully would produce a vivid and highly prized red color. After several decades this technique spread from Korea to China and was a precursor to the Yüan underglaze red porcelains. Other Koryo and Yi experiments involved iron decoration and iron glazes rather than pure celadon glazes. -- AATA