A ceramic artifact is one made of terracotta at a temperature of at least 500oC. At this temperature the effects of temperature are irreversible and the clay soil becomes ceramic. The permeability of ceramic products can be used as a criterion for the simplest classification of earthenware (permeability above 5%) and hard ceramics, which can be classified in many different ways according to the The soil that people use and the heating temperature:
+ 500 -900oC: earthenware at low temperature.
+ 900 -1,150oC: earthenware.
+ 1,150 -1,300oC: hard pottery.
+ 1,300 -1,450oC: porcelain.
The term “bisquit bake” refers to the fact that heating an object of earth turns into a biscuit-like state. Next, one glazed and decorated and then fired a second time, unless the carpentry was left unglazed.
“Underglazed enamel” is applicable to the first freshly baked porcelain and followed by enameling and then burning. So the decorative details are enameled and protected.
Colors painted on glaze or colors painted with enamel (overglazed enamel) are coated on the surface. Therefore, they are less resistant to rubbing and abrasion, less durable than decorative colors under enamel. However, people use a variety of colors in the form of paint on glazes when heated at lower temperatures.
Sun-dried mud objects such as bricks, numbers and wedge-shaped inscriptions (like ancient Persian and Assyrian) will serve as part of the pottery collection, but are not heated. If left they in water for a while, these artifacts will decay.
1. Terracotta pottery (Earthenware)
The term “baked clay ceramics” refers to handcrafted wares that are classified from raw to fine, generally having practical uses, carved or painted for decoration. One can perform a surface finishing by many different steps to increase the waterproofing ability or to decorate. Polishing can be carried out in the pre-firing stage to produce an excellent finish and increase water repellency (eg for Villanovan artifacts). A thin coat (made of a smoothed clay) is applied to the surface at the reinforcement stage before firing. This is more fragile than glazed (such as red and black Attic wares, Arrentine and Samian wares). White coatings are particularly fragile and easily stain (eg Greek white porcelain).
2. Uncoated red brown ceramic (Terracotta)
Unglazed reddish-brown wares (terracotta) are heated at approximately 950 ° C. Uncoated sepia can be tiny earth statues, but sometimes very large objects such as incensory, reliefs and architectural decorations. They are molded, and usually unglazed, but have an external “heating shell” during wet clay prototyping prior to being placed in the kiln.
Sometimes before firing, at the stage of making coats, people decorate in plain white or if decorated in sections, it is done before and after firing (for example, statues of Greek Tanagra terracotta) . Occasionally, unglazed red brown ceramic objects are covered with a layer of lime, then decorated in sections and / or gilded (Etruscan urns).
3. Glazed earthenware (Glazed earthenware)
Glazed terracotta wares are classified according to their glaze and decorative characteristics. The enamel is made from glass and bound to the ceramic during the second firing. Glazed baked clay wares include white ceramics, ivory and jade ceramics and all Staffordshire ceramics. Tin-colored glazed ceramics include Delft, Faience and Maiclica ceramics.
There are three main types of porcelain: hard porcelain, porous porcelain, and porcelain made of clay and bone china. Hard and porous porcelain are both heated at temperatures between 1,200oC and 1,450oC. “Hard” corresponds to porcelain fired at a temperature of about 1,450 ° C and “light porous” corresponds to a heating temperature of about 1,200 ° C.
a. Hard porcelain:
Hard porcelain is also considered “real” or “heated porcelain”. It is made from heat-resistant white clay (kaolines) and a type of longstone rock that has been cooked into glass and is usually white in color. When thin, it’s translucent. The soil and glaze are mixed together to create a very thick layer of enamel, which makes this type of porcelain very hard. This type was first made in China in AD 900, but not as successful as the one made in Europe later in 1700 in Meissen when the technique had matured. These Vietnamese, Chinese and Japanese porcelain, Meissen porcelain, Vienna porcelain, Sèvre porcelain, Plymouth porcelain and Bristol porcelain are illustrative examples.
Vietnamese cream enamel tableware
b. Soft porcelain
This type of porcelain is also considered “imitation” porcelain or “low temperature burning porcelain”. People tried to imitate real Asian (China, Vietnam, Japan…) porcelain and made it in different ways but all contained glass. They are porcelain like Medici, Capodimonte, Routen, Vincennes, Bow, Chelsea, Worcester.
c. Beautiful porcelain made of clay and bone ash (Bone china):
This type of porcelain is truly altered by adding bone ash to the finest quality clay (kaolines) and terrestrial rocks. In England, ashes were added to real and artificial porcelain and porcelain around 1800 and the technique rarely crossed the British borders. Firing this kind of fine porcelain is different from the process of making porcelain. The process of baking unglazed porcelain is conducted at a temperature of about 1,300oC, and then enameled at a lower temperature, about 1,100oC.