A blue–green dish held in the British Museum — long thought from Korea — has been shown to be one of less than 100 known pieces of the rarest type of Chinese pottery. Dating back some 900 years to the time of Imperial China's Song dynasty, 'Ru official ware' was noted for its lack of decoration and typically pale, 'duck-egg' blue glaze. Produced only for a short period between 1086–1125 CE, Ru ware was produced exclusively for the use by members of the Northern Song Imperial court. According to experts, the secret to Ru ware lay in its manufacture at...