Potteries

Potteries

[Login to edit this page]

Pottery is made by forming a clay body into objects of a required shape and heating them to high temperatures in a kiln to induce reactions that lead to permanent changes, including increasing their strength and hardening and setting their shape. There are wide regional variations in the properties of raw materials used for the production of pottery, and this can lead to wares that are unique in character to a locality. It is common for clays and other materials to be mixed to produce clay bodies suited to specific purposes.

Prior to some shaping processes, air trapped within the clay body needs to be removed. This is called de-airing and can be accomplished by a machine called a vacuum pug or manually by wedging. Wedging can also help to ensure an even moisture content throughout the body. Once a clay body has been de-aired or wedged, it is shaped by a variety of techniques. After shaping it is dried before firing. There are a number of stages in the drying process. Leather-hard refers to the stage when the clay object is approximately 15% mositure content. Clay bodies at this stage are very firm and only slightly pliable. Trimming and handle attachment often occurs at the leather-hard state. Clay bodies are said to be "bone-dry" when they reach a moisture content at or near 0%. Unfired objects are often termed greenware. Clay bodies at this stage are very fragile and hence can be easily broken.

Pottery can be shaped by a range of methods that include:

Hand building. This is the earliest forming method. Wares can be constructed by hand from coils of clay, from flat slabs of clay, from solid balls of clay, or some combination of these. Parts of hand-built vessels are often joined together with the aid of slip, an aqueous suspension of clay body and water. Hand building is slower than wheel-throwing, but it offers the potter a high degree of control over the size and shape of wares. The speed and repetitiveness of other techniques is more suitable for making precisely matched sets of wares such as tablewares, although some studio potters find hand building more conducive to create one-of-a-kind works of art.

The potter's wheel. In the process that called "throwing" (coming from the Old English word thrawan, which means to twist or turn), a ball of clay is placed in the center of a turntable, called the wheel-head, which the potter rotates with a stick, with foot power or with a variable speed electric motor.

During the process of throwing the wheel rotates rapidly while the solid ball of soft clay is pressed, squeezed and pulled gently upwards and outwards into a hollow shape. The first step of pressing the rough ball of clay downward and inward into perfect rotational symmetry, is called centering the clay, a most important skill to master before the next steps: opening (making a centered hollow into the solid ball of clay), flooring (making the flat or rounded bottom inside the pot), throwing or pulling (drawing up and shaping the walls to an even thickness), and trimming or turning (removing excess clay to refine the shape or to create a foot).

Considerable skill and experience are required to throw pots of an acceptable standard, and whilst the ware may have high artisitic merit the reproducibility of the method is poor. Because of its inherent limitations, throwing can only be used to create wares with radial symmetry on a vertical axis. These can then be altered by impressing, bulging, carving, fluting, and incising. In addition to the potter's hands these techniques can use tools, including paddles, anvils & ribs, and those specifically for cutting or piercing such as knives, fluting tools & wires. Thrown pieces can be further modified by the attachment of handles, lids, feet and spouts.

Granulate pressing: As the name suggests, this is the operation of shaping pottery by pressing clay in a semi-dry and granulated condition in a mould. The clay is pressed into the mould by a porous die through which water is pumped at high pressure. The granulated clay is prepared by spray-drying to produce a fine and free flowing material having a moisture content of between about five and six per cent. Granulate pressing, also known as dust pressing, is widely used in the manufacture of ceramic tiles and, increasingly, of plates.

Injection Moulding: is a shape forming process adapted for the tableware industry from the method long established for the forming of thermoplastic and some metal components. It has been called Porcelain Injection Moulding, or PIM. Suited to the mass production of complex-shaped articles one significant advantage of the technique is that it allows the production of a cup including the handle in a single process, and thereby eliminating the handle fixing operation and producing a stronger bond between cup and handle. The feed to the mould die is a mix of approximately 50 - 60% unfired body, in powder form, together with 40 - 50 % organic additives composed of binders, lubricants and plasticisers. The technique is not as widely used as other shaping methods.

Jiggering and jolleying: These operations are carried out on the potter's wheel and allow the time taken to bring wares to a standardized form to be reduced. Jiggering is the operation of bringing a shaped tool into contact with the plastic clay of a piece under construction, the piece itself being set on a rotating plaster mould on the wheel. The jigger tool shapes one face whilst the mould shapes the other. Jiggering is used only in the production of flat wares, such as plates, but a similar operation, jolleying, is used in the production of hollow-wares, such as cups. Jiggering and jolleying have been used in the production of pottery since at least the 18th century. In large-scale factory production jiggering and jolleying are usually automated, which allows the operations to be carried out by semi-skilled labor.


0 Comments

Write a comment

Rating:    

Share On Facebook
Search And Find
Epik Search:
Join The Epik Network
Join Now:

Browse The Epik Network

  • Potteries

    Noliaclap

    Noelfisher

    Billmacy

    Passyouby

    Norah-jones

    Taliabalsam

    Raulmondesi

    Tahneewelch

    Torda

    Henrynixon

    Noellebeck

    Noahlowry

    Marianalevy

    Noteveo

    74

    Floristeria

    Noelbarber

    Milliliter

    Rochcarrier

    Say-goodbye