Giving Shape to Clay
Much of the beauty of pottery depends on the manner in which clay is shaped and this could be achieved via several methods. Some of the methods that are universally followed to give shape to clay are discussed as follows -
Shaping by hand
Credited with being the first method for creating objects, using hands for shaping entails handling slabs, balls or coils of clay and transforming them with the help of water into desired shapes. Like shapes, decoration is also subject to customization and can be adorned irrespective of whether it has been subjected to fire treatment.
Shaping on the potter's wheel
Giving shape to clay on the potter's wheel is known as 'throwing' and it entails placing of a lump of clay on the wheel-head, meaning the center of the wheel, so that it begins to take shape when the wheel is rotated. Usually rotation occurs through the efforts of the potter wherein he uses his foot and a stick to maintain a steady speed but modernization has cleared the path for using an electric motor to achieve this purpose.
There are several steps that constitute the process of throwing, namely centering, opening, flooring, throwing and trimming. All of these require a certain degree of expertise and an inherent flair goes a long way in mastering each of these techniques. Owing to the nature of tools employed, objects produced by throwing feature radial symmetry and are aligned as per the vertical axis. Since their surface is plain, adornment is provided through paintaing, carving, incising and adding of accessories like lids, spoons and so on.
Also referred to as 'dust pressing', this process has been found to be particularly effective in the manufacture of ceramic flat objects like tiles and plates. It entails pressing of semi-dry granulated clay into a mould and then subjecting it to a steady stream of porous dye and water.
Moulding by injection
Usually employed for producing tableware, this process entails mixing powdered clay with organic additives in the ratio of 6:4 wherein the latter act as lubricants or binders. A specialty of this method is that it can be used to produce a cup or a jar with a handle, thus eliminating the need for creating extra fixtures.
This is an operation wherein a shape tool is brought into contact with a piece of clay that is still in the process of being moulded. As a result, while the mould provides shape to one face of the tool, the shape tool helps create the opposite face. Jiggering is mostly used for creating plates.
Used in conjuction with jiggering is jolleying, another process which is very similar but is employed for producing holloware like cups, jars and so on.
Using Roller-head Machine
Introduced in Britain soon after the Second World War, the roller head machine was immediately embraced by artisans the world over and since then remains a universally accepted procedure for creating flat objects. While in concept it is very similar to jiggering and jolleying, a difference that sets its apart pertains to replacement of the fixed tool by a shallow and cone-like rotart shaping tool which is of the same diameter as the requisite flatware.
Being mechanized, this procedure is much quicker as compared to the manual methods wherein it is possible to churn out as many as 12 pieces within the span of a minute but its true attraction lies in ease of operation which does not require any prior expertise.
Having evolved during the 1970s', this method calls for application of high external pressure on polymer mould so that it takes lesser duration to cast and in this way, speeds up the rate of production. Not only are polymeric moulds more durable than plaster moulds but are also ready for use almost immediately since their drying time is minimal. One of the segments for which this method has been found to be particularly effective is production of sanitaryware.
When a particular object is given shape by pressing a body of clay bearing the same shape between two moulds of high porosity, the process is referred to as RAM pressing. Subsequent to having been pressed, the shaped objects are separated by blowing compressed air through the moulds.
Only when you have run out of methods for shaping a particular object should you resort to slip casting wherein a 'slip' of clay and water is poured into a mould of plaster having high absorbency. While the plaster absorbs the water, the clay is left to dry, thus taking the shape of the mould. Sanitary ware is one segment which makes extensive use of this method but it has been found to be equally effective in production of figurines too.