Pottery

Pottery is a form of ceramics technology, where wet clays are shaped and then dried or fired to harden them. The term is generally used only for relatively easily constructed utensils such as pots, cups, bowls, etc., and for decorative items but not for complex ceramics like Space Shuttle tiles. Pottery is an ancient technology.

A person who makes pottery is generally known as a potter.

A man shapes pottery as it turns on a wheel. (Cappadocia, Turkey)

Techniques

Forming Techniques

There are three basic categories of forming techniques used in pottery - handwork, wheelwork, and slipcasting. It's very common for wheelworked pieces to be finished by handwork techniques. Slipcast pieces tend not to be, as that negates one of the prime advantages of casting.

Handwork methods are the most primitive and individual techniques, where pieces are constructed from hand-rolled coils, slabs, ropes and balls of clay, often joined with a liquid clay slurry. No two pieces of handwork will be exactly the same, so it is not suitable for making matched sets of items e.g. dinnerware. Doing handwork enables the potter to use their imagination to create one-of-a-kind works of art.

The potter's wheel can be used for mass production, although often it is employed to make individual pieces. A ball of clay is placed in the center of a turntable, called the wheel head, which is turned chiefly using foot power (a kick wheel or treadle wheel) or a variable speed electric motor. Oftentimes a disk of plastic, wood, or plaster is affixed to the wheel head and the ball of clay attached to the disk rather than the wheel head so as to facilitate easy removal of the finished piece. This disk is referred to as a bat. The wheel revolves rapidly while the clay is pressed, squeezed and pulled gently into shape. The process of pressuring the clay into a radial symmetry, so that it does not move from side to side as the wheel head rotates is referred to as "centering" the clay - usually the most difficult skill to master for beginning potters. Wheel work takes a lot of technical ability, but a skilled potter can produce many virtually identical plates, vases or bowls in a day. Because of its nature, wheel work can only be used to initially create items with radial symmetry on a vertical axis. These pieces can then be altered by impressing, bulging, carving, fluting, faceting, slicing, and other methods to make them more visually interesting. Often, thrown pieces are further modified by having handles, lids, feet, spouts, and other functional aspects added using the techniques of handworking. There are two related techniques that improve repeatability of wheelwork. A jigger is a mould that is slowly brought down onto the outside of an object, whilst it is being turned on a wheel. A solid mould is used to form the inside of the piece. Similarly, a jogger is used to shape the inside of a piece, pressing the outside against a solid mould

Slipcasting is probably the easiest technique for mass-production. A liquid clay slip is poured into plaster moulds and allowed to harden slightly. Once the plaster has absorbed most of the liquid from the outside layer of clay the remaining slip is poured back into the storage tub, and the item is left to dry. Finally the finished item is removed from the mould, trimmed neatly and allowed to air-dry.

Decorative and finishing techniques

Clay additives can be used to give colour to the clay, prior to working. Various coarse additives can also be added. Sands and other grogs give the final product texture, and contrasting coloured 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 analogue 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.

An ancient Armenian Urn

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 (often a mix of dolomite, frit, flint, feldspar, sodium borate, clay and whiting). 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

Incipient Jomon pottery (10,000-8,000 BC), Tokyo National Museum, Japan.

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, Syria and south-eastern Turkey, the earliest finds of clay pots date from Neolithic times, around the 8th millennium BC (black burnished ware). Before that, clay had been used to make statuettes of humans and animals that were sometimes burned as well. In the preceding Pre-Pottery Neolithic, vessels made of stone, gypsum and burnt lime (vaiselles blanches or white ware) had been used. Sometimes a mixture of clay and lime was used, not very successfully, in the earliest pottery.

see history of pottery in Palestine
Nevala Cori for figurines