This question attracted a good number of candidates and the performance was above
average.
However, some candidates demonstrated lack of knowledge of the processes of
preparing clay, as well as its properties.
Some of the following were expected in the candidates' responses:
1 (a)Classes of Clay
(i) Primary clay.
(ii) Secondary clay.
(b)Processes of preparing Clay for Moulding
A lump of clay consists of soil particles and impurities which must be
removed by sieving.
Break lumps of dry clay into pieces using pestle and mortar.
Dissolve the pieces of clay in water container.
Sieve the clay.
Leave the sieved clay for some time, so that the fine clay settles at
the bottom of the container.
Pour the excess water off and keep the fine clay in a clean
container or dug-up pit.
Dry the clay partially.
When it is partially dried, knead and wedge the clay.
Store the clay in the polythene bag, ready for use.
(c)Properties of Clay
For Primary Clay
less plastic in nature - i.e. rate of its quality of being easily made
into any shape is very low.
It is matured/fired at high temperature.
It is less contaminated.
It is highly porous in nature.
After firing, it becomes white/near white.
Secondary Clay
Highly plastic in nature.
It is matured/fired at low temperature.
It is highly contaminated.
It has low porosity. After firing, it comes in different colours. |
