The potter's most basic tool is the hand. However, many additional tools have been developed over the long history of pottery manufacturing, including the potter's wheel and turntable, shaping tools (paddles, anvils, ribs), rolling tools (roulettes, slab rollers, rolling pins), cutting/piercing tools (knives, fluting tools, wires) and finishing tools (burnishing stones, rasps, chamois).
Pottery can be shaped by a range of methods that include:
Handwork or hand building. This is the earliest and the most individualized and direct 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 slurry or slip, a runny mixture of clay and water. Hand building is slower and more gradual than wheel-throwing, but it offers the potter a high degree of control over the size and shape of wares. While it isn't difficult for an experienced potter to make identical pieces of hand-built pottery, the speed and repetitiveness of wheel-throwing is more suitable for making precisely matched sets of wares such as table wares. Some studio potters find hand building more conducive to fully using the imagination to create one-of-a-kind works of art, while others find this with the wheel.
The potter's wheel. In the process that is called "throwing" (coming from the Old English word thrawan, which means to twist or turn [1]) , a ball of clay is placed in the center of a turntable, called the wheel-head, which the potter rotates with a stick, or with foot power (a kick wheel or treadle wheel) or with a variable speed electric motor. (Often, a disk of plastic, wood or plaster — called a bat — is first set on the wheel-head, and the ball of clay is thrown on the bat rather than the wheel-head so that the finished piece can be removed intact with its bat, without distortion.)
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 (and often most difficult) 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).
From around 7th century BC until the introduction of slip casting in the 18th century AD, the potter's wheel was the most effective method of mass producing pottery, although it is also often employed to make individual pieces. Wheel-work makes great demands on the skill of the potter, but an accomplished operator can make many near-identical plates, vases, or bowls in the course of a day's work. Because of its inherent limitations, wheel-work can only be used to create wares with radial symmetry on a vertical axis. These can then be altered by impressing, bulging, carving, fluting, faceting, incising, and by other methods making the wares 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.
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.
Roller-head machine: This machine is for shaping wares on a rotating mould, as in jiggering and jolleying, but with a rotary shaping tool replacing the fixed profile. The rotary shaping tool is a shallow cone having the same diameter as the ware being formed and shaped to the desired form of the back of the article being made. Wares may in this way be shaped, using relatively unskilled labor, in one operation at a rate of about twelve pieces per minute, though this varies with the size of the articles being produced. The roller-head machine is now used in factories worldwide.
RAM pressing: A factory process for shaping table wares and decorative ware by pressing a bat of prepared clay body into a required shape between two porous molding plates. After pressing, compressed air is blown through the porous mould plates to release the shaped wares.
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.
Slipcasting: is often used in the mass-production of ceramics and is ideally suited to the making of wares that cannot be formed by other methods of shaping. A slip, made by mixing clay body with water, is poured into a highly absorbent plaster mold. Water from the slip is absorbed into the mould leaving a layer of clay body covering its internal surfaces and taking its internal shape. Excess slip is poured out of the mold, which is then split open and the molded object removed. Slipcasting is widely used in the production of sanitary wares and is also used for making smaller articles, such as intricately-detailed figurines.
No comments:
Post a Comment