Decorative and finishing techniques
Clay additives can be used to give color to the clay, prior to working. Various coarse additives can also be added. Sands and other grogs give the final product texture, and contrasting colored clays and grogs result in patterns. Combustible particles can be mixed with clay or pressed into the surface, to give textures.
Agateware refers to techniques that give a mixture of coloured clays. The name is derived from agates, which show band of colours, although it can be made with any sort of clay. Two different colours of clay are lightly kneaded together, before being formed into a shape. Although, in principle, any clays can be used, differing rates of drying and expansion in firing mean that it is usual to use a light colourless clay, and add a colourant to part of it. An analog of marquetry can also be made, by pressing small blocks of coloured clays together.
Burnishing, like the metalwork technique of the same name, involves rubbing the surface of the piece with a polished surface (typically steel or stone), to smooth and polish the clay. Finer clays give a smoother and shinier surface than coarser clays, as will allowing the pot to dry more before burnishing, although that risks breakages.
To give a finer surface, or a coloured surface, a thin slurry of clay called slip can be coated on to the dry clay. This can be painted with, or the piece can be dipped for a uniform coating. Sgraffito involves scratching through a layer of coloured slip to reveal a different colour underneath. One colour of slip can be fired, before a second is applied prior to scratching, if the base clay is not of the desired colour or texture.
Glazing is the process of coating the piece with a thin layer of a glassy material. This is important for functional earthenware vessels, which would otherwise be unsuitable for holding liquids due to porosity. Glaze may be applied by dusting it over the clay, or dipping or brushing on a thin slurry of glaze and water. Brushing tends not to give very even covering, but can be effective with a second coating of a coloured glaze as a decorative technique. With all glazed items, a small part of the item (usually on the base of the piece) must be left unglazed, else it will stick to the kiln during firing.
Production stages
All pottery items go through a series of stages during construction.
- The raw clay is wedged to make its moisture and other particle distribution homogeneous and to remove air bubbles. It is then shaped either by hand or using tools such as a potter's wheel, an extruder, or a slab roller. Water is used to keep the clay flexible during construction and to keep it from cracking.
- Work that is thrown on the wheel often needs to be trimmed or turned to make its thickness uniform and/or to form a foot on the piece. This process is done when the piece has dried enough to survive this manipulation.
- The piece is allowed to air dry until it is hard and dry to the touch. At this stage it is known as greenware. Items of greenware are very brittle but they can be handled with care. Greenware items are often sanded with fine grade sandpaper to ensure a smooth finish in the completed item.
- Sometimes the greenware is given a coating of a liquid clay slip. This is most often done to give a coloured base for decoration, other than the colour of the main clay.
- The greenware is often given a preliminary firing in a kiln. Once it has been fired once it is known as 'biscuit' ware or bisque.
- Biscuit ware is normally a plain red, white or brown colour depending on which type of clay is used. This is decorated with glaze and then fired again to a higher temperature.
- Some pieces are not bisque-fired before being glazed. These pieces are called once-fired.
History
Palaeolithic Pottery
Pottery found in the Japanese islands has been dated, by uncalibrated radiocarbon dating, to around the 11th millennium BC, in the Japanese Palaeolithic at the beginning of the Jomon period. This is the oldest known pottery.
In Europe, burnt clay was already known in the late Palaeolithic (Magdalenian) and was used for female figurines, like the "Venus" of Dolni Vestonice.
Neolithic pottery
In Palestine, the earliest finds date from Neolithic times, around the 8th millennium BC, when the art of pottery was introduced into the region ? probably from the north, together with the agriculture. See full article history of pottery in Palestine.
See also
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