The blue pigment used to create the painted decoration on this teapot is taken from the ground mineral cobalt oxide. The pigment was mixed with water and applied with a brush to the unfired porcelain surface, which was then covered with a clear glaze before firing in the kiln. Referred to as ‘nameless rarity’ (wuming yu) or Mohammedan blue (huiqui qing), the mineral was imported from Iran and was a costly material which was difficult to obtain in vast quantities. Cobalt was first used to decorate Chinese ceramic wares in the 1st century AD, but the widespread production of blue and white porcelain only emerged in the second half of the 14th century. Blue and white porcelain dominated the Chinese export trade until the end of the 17th century, and was immensely popular in Vietnam, the Middle East and later in Europe, where it was collected in vast quantities and highly valued by the wealthy.