About Ceramics Clay
Ceramics is the fine art of manipulating clays into hardened shapes. The
objects made out of this art form are called ceramics clay. They serve
as items of utility and beauty in homes and offices. Ceramics clay could
even be shaped into highly esthetical forms, which are classified as ceramic
art.
Generally, ceramics clay articles are made by moistening a mixture of
clays, then casting it into desired shapes and then firing it to a high
temperature. This makes the clay hardened in a process known as vitrification.
Clay has several unique properties that enable it to be used for
ceramic art.
I. Clay has a property of plasticity. When an external pressure is applied
to an object and it keeps that shape, then that object is called as plastic.
Clay possesses this property, which makes it possible to give it a permanent
shape.
II. Another property of clay is that it shrinks when it is fired in kilns.
This is a setting process, which allows the clay to become hard and retain
the shape that is given to it.
III. Clay molecules can remain attached to each other. This process is
called as cohesion. Also, clay molecules stick very close to each other
without leaving many pores, due to which clay is an ideal material to
make ceramic vessels.
IV. When clay is totally dried, then its surface can be painted. This
makes it possible to decorate the surface in several ways.
Clay is actually a mixture of several minerals. Depending on the composition,
there are different types of clays. The main types of clays used in ceramics
are as follows:-
I. China clay (kaolin) – Kaolin is a silicate clay,
with the chemical composition of Al2Si2O5(OH)4. It is considered to be
the richest form of clay used in the ceramics clay industry. This clay
is pure white in color and it retains that color when the article is made.
The degree of purity of china clay ceramics is adjudged on the basis of
its whiteness. However a pinkish or orange red hue can be obtained in
kaolin by the addition of some amount of iron oxide.
II. Ball Clay – Ball clay is a further metamorphosis
of kaolin which deposits in swampy areas. Here, the acids formed due to
decomposition of vegetal and animal matter can break the kaolin to still
finer particles. The result is, the cohesion properties increase, but
the whiteness gets reduced. Ceramics made of ball clay are much harder
than those made of china clay.
III. Fireclays – As their name suggests, fireclays
are ceramics clay that can withstand high temperatures. They are commonly
used to make utility wares such as those which are used in chemical laboratories.
This is actually a name given to different kinds of clays whose composition
consists of high amounts of aluminum and silicates, but they have little
amounts of iron in them. Feldspar and calcium are absent in all kinds
of fireclays.
IV. Earthenware clays – These are similar to fireclays
in their composition, but they cannot withstand as high temperatures.
Earthenware clays are used to make utensils and utility items, such as
water pots and urns. They are attached by cohesion at low firing temperatures
in kilns, and thus even small scale potters can create them. They are
also called as potters' clay. However, earthenware clays could require
several fluxes for their formation into ceramics, such as iron oxides.
This makes the surfaces of this ceramics clay quite rough and highly porous.
Smooth vitrification does not occur in earthenware clays.
V. Stoneware clays – These are the cheapest and
the most abundantly found varieties of clay used in ceramics clay range.
They are gray to brown in color. These clays are highly impure with iron,
calcium and feldspar, due to which they require a higher hardening temperature.
VI. Porcelain clays – Porcelain is heat-resistant
and the most good-looking in the ceramics clay family. Thus its sheer
beauty it is widely used in making crockery like dinner plates. It is
pure white clay and keeps that color after the firing process. It is a
daunting task to make ceramic ware from porcelain since it has a tendency
to crack when drying. For this reason, hand building is difficult with
this type of clay.
The final quality of the ceramics clay item depends greatly on the type
of clay that is being used. Ultimately, it is the clay that will decide
how cheap or expensive the ceramics clay item will be.
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