"Blue and white pottery" (Chinese: 青花瓷; pinyin: qīng-huā cí; lit. 'Blue flowers/patterns') covers a wide range of white pottery and porcelain decorated under the glaze with a blue pigment, generally cobalt oxide. The decoration was commonly applied by hand, originally by brush painting, but nowadays by stencilling or by transfer-printing, though other methods of application have also been used. The cobalt pigment is one of the very few that can withstand the highest firing temperatures that are required, in particular for porcelain, which partly accounts for its long-lasting popularity. Historically, many other colours required overglaze decoration and then a second firing at a lower temperature to fix that.
The origin of the blue glazes is thought to lie in Iraq, when craftsmen in Basra sought to imitate imported white Chinese stoneware with their own tin-glazed, white pottery and added decorative motifs in blue glazes. Such Abbasid-era pieces have been found in present-day Iraq dating to the 9th century AD, decades after the opening of a direct sea route from Iraq to China. According to Jonathan Bloom, these 9th and 10th century Iraqi examples were the first blue-and-white wares. This technique was transmitted to Europe during the Arab conquest of Spain and North Africa and is also believed to have influenced Chinese ceramics through the activities of Muslim traders. The influence of Islamic pottery can be clearly seen in the work of Gongxian potters when they switched to making stonewares for use in daily life. Instead of drawing from the typical repertoire of Tang ornamentation, their angular lozenge motifs and palmettes look like a direct take on Mesopotamian quatrefoil panels filled with Arabic writing and surrounded by leaf fronds.
