English porcelain dating
Another early method is once-fired where the glaze is applied to the unfired body and the two fired together in a single operation.
In this process, green (unfired) ceramic wares are heated to high temperatures in a kiln to permanently set their shapes.
Many types of glaze, such as the iron-containing glaze used on the celadon wares of Longquan, were designed specifically for their striking effects on porcelain. Porcelain wares may be decorated under the glaze using pigments that include cobalt and copper or over the glaze using coloured enamels.
Like many earlier wares, modern porcelains are often biscuit-fired at around 1,000 °C (1,830 °F), coated with glaze and then sent for a second glaze-firing at a temperature of about 1,300 °C (2,370 °F) or greater.
The clays used are often described as being long or short, depending on their plasticity.
Long clays are cohesive (sticky) and have high plasticity; short clays are less cohesive and have lower plasticity.
The toughness, strength, and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and the formation of the mineral mullite within the body at these high temperatures.Porcelain slowly evolved in China and was finally achieved (depending on the definition used) at some point about 2,000 and 1,200 years ago, then slowly spread to other East Asian countries, and finally Europe and the rest of the world.Its manufacturing process is more demanding than that for earthenware and stoneware, the two other main types of pottery, and it has usually been regarded as the most prestigious type of pottery for its delicacy, strength, and its white colour.The following section provides background information on the methods used to form, decorate, finish, glaze, and fire ceramic wares.Unlike their lower-fired counterparts, porcelain wares do not need glazing to render them impermeable to liquids and for the most part are glazed for decorative purposes and to make them resistant to dirt and staining.