The art of using clay to make various objects is called pottery.
Clay must be prepared before use in pottery. Any trace of sand is
removed. The clay is mixed with water and pounded as in to
remove air bubbles and also to make the clay more plastic so that
becomes easier to mould and shape. If sand and air bubbles are
not removed, any article made from such clay may explode or
crack during the period of heating the freshly moulded article.
There are different ways in which the prepared clay can be used
to mould different articles. The simplest way to make a pot is by
the pinch pot method’
A hollow is first formed with the thumb in a small ball of clay.
By carefully pressing between the fingers, the wall is gradually
made thinner as the form develops. The final form, containing
some cracks, is then smoothed by using fingers and a small
quantity of water.
The Potter’s Wheel
The pinch pot method does no involve any apparatus. Most
pottery articles are made by using what is called the ‘potter’s
wheel’. A potter’s wheel is a device with a rotating horizontal disc
upon which clay is moulded by a potter
Any article just moulded from clay is soft. To harden the moulded
article, it is baked in a fire. One simple way of baking is by using firewood.
A more sophisticated way of heating is by using what is
called a kiln. A kiln is an oven or furnace for baking finished
articles. Different kilns use different fuels to produce fire fo
baking. Such fuels include wood, coal, oil and gas. An example of
a kiln using gas is shown in Fig. 6.14. The hot air transfers heat to
the finished pieces as it travels through the chamber
In order to make mud, we dig pure earth which docs not contain
Sand. It is moistened with water, and made plastic by pounding
with feet. The soft mud is then pressed by hand into a wooden
mould. The soft bricks are dried initially by exposing them to the
Sun: They ale made stronger by baking them later on using
Concrete blocks arc made by mixing cement, aggregate and sand
with water. The mixture is turned into a uniform paste by using a Shovel or a concrete mixer. The paste is then shoveled into aa
moulding machine. The moulded blocks are removed and placed
on level ground to dry. The blocks are ready for use after drying
for some days.
There are many ways of making plastics from the molten måterial.
The choice of method depends upon the plastic product to be made
and its use. The typical methods of processing plastics are
Compression moulding, Injection mouldin, Vacuum forming,
Extrusion, Calendering. These methods arc described below.
Compression moulding is the forcing of a material into a mould
with pressure and heat This is one of the methods of
processing thermoset materials. The moulding material or resin is
first heated in an oven. It is then poured into the open cavity in the
lower part of the mould. This lower part is called the female
section of the mould. The plunger, or male section of the mould,
moves down to close the mould. The pre-heating of the material in
the oven is not sufficient to mould the plastic. So the material is
subjected to further heating by either electricity or steam. The
material is pressed by forcing the male section down into al
cavities or the mould.
During the process, the material hardens into a permanent
shape. The mould is then opened and the finished product is taken
This method or moulding is generally used for thermoplas.
materials. In injection moulding, the mould is not heated as in
compression moulding. The kind or thermoplastic, in terms or colour and quality, is
selected and red into the reed hopper in powder form. The plastic
material is heated in the heating chamber between the hopper and
the mould. The right amount or heated material is then forted by
the plunger into the mould. The plastic is formed as it is forced
into the mould. The article stays in the mould until it is completely
cool. Then it is removed. Plastic products such as valves and the
air-intake grill or an air conditioner and nylon hair comb are made
by the injection moulding method.