Overglaze decoration in the context of "Mina'i ware"

"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.

Underglaze is a method of decorating pottery in which painted decoration is applied to the surface before it is covered with a transparent ceramic glaze and fired in a kiln. Because the glaze subsequently covers it, such decoration is completely durable, and it also allows the production of pottery with a surface that has a uniform sheen. Underglaze decoration uses pigments derived from oxides which fuse with the glaze when the piece is fired in a kiln. It is also a cheaper method, as only a single firing is needed, whereas overglaze decoration requires a second firing at a lower temperature.

Many historical styles, for example Persian mina'i ware, Japanese Imari ware, Chinese doucai and wucai, combine the two types of decoration. In such cases the first firing for the body, underglaze decoration and glaze is followed by the second firing after the overglaze enamels have been applied. However, because the main or glost firing is at a higher temperature than used in overglaze decoration, the range of colours available in underglaze is more limited, and was especially so for porcelain in historical times, as the firing temperature required for the porcelain body is especially high. Early porcelain was largely restricted to underglaze blue, and a range of browns and reds. Other colours turned black in a high-temperature firing.

Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C (1,380 and 1,560 °F). The powder melts, flows, and then hardens to a smooth, durable vitreous coating. The word vitreous comes from the Latin vitreus, meaning "glassy".

Enamel can be used on metal, glass, ceramics, stone, or any material that will withstand the fusing temperature. In technical terms fired enamelware is an integrated layered composite of glass and another material (or more glass). The term "enamel" is most often restricted to work on metal, which is the subject of this article. Essentially the same technique used with other bases is known by different terms: on glass as enamelled glass, or "painted glass", and on pottery it is called overglaze decoration, "overglaze enamels" or "enamelling". The craft is called "enamelling", the artists "enamellers" and the objects produced can be called "enamels".

Coalport, Shropshire, England was a centre of porcelain and pottery production between about 1795 ("inaccurately" claimed as 1750 by the company) and 1926, with the Coalport porcelain brand continuing to be used up to the present. The opening in 1792 of the Coalport Canal, which joins the River Severn at Coalport, had increased the attractiveness of the site, and from 1800 until a merger in 1814 there were two factories operating, one on each side of the canal, making rather similar wares which are now often difficult to tell apart.

Both factories made mostly tablewares that had elaborate overglaze decoration, mostly with floral subjects. A further round of mergers in 1819 brought moulds and skilled staff from Nantgarw porcelain and Swansea porcelain to Coalbrookdale, which continued to thrive through the rest of the century. The Coalport factory was founded by John Rose in 1795; he continued to run it successfully until his death in 1841. The company often sold its wares as Coalbrookdale porcelain, especially the pieces with flowers modelled in three dimensions, and they may be called Coalport China.