Celadon is a pale greyish shade of green, or rather a range of such shades. Celadon originates as a term for a class of Chinese ceramics, copied by Korea and Japan. However, the name, which is European, may originate from the character Celadon in L'Astrée, a French pastoral novel of 1627, who wore a light green color. Celadon glazes were very common, with the green color being reliably produced from about the tenth century onwards; this was appreciated in Asia for resembling jade, the most prestigious material of all. The glaze color comes from iron oxide's transformation from ferric to ferrous iron during the firing process, but is affected by a wide range of other factors and chemicals, making the precise color very difficult to control. As well as green, a wide range of browns, yellows, greys and sometimes blues all count as "celadon".