2 Testing,
improving the
quality and
manufacturing
clay
Pic 6. The mud should be mixed with water to form a
sticky substance.
CLAY BASED
TECHNOLOGIES
One of the most important tasks for those wishing
to make technologies from clay is to find out the
quality of the clay in the area. There are a number
of indigenous ways of doing this which do not require
excessive amounts of measuring equipment, three
of these are outlined below. However if you desire
more accurate ways of determining the quality of clay,
please contact the Practical Answers Team.
2.1. Shrink Test
a) Choose a small amount of soil that is to be tested
and mix it into a dough like mixture. Put the
mixture on a plastic sheet and beat it to remove air
and produce a good consistent mixture.
b) Following this the mixture should be rolled between
your hands until it is long and thin, measuring 10
cm in length and then left to dry for 24 hours.
Using the rule it should be measured again to see
how much the clay has shrunk. Ideally for good
quality clay it should not have shrunk more than
10% of its length. Therefore, in this example it
should still be at least 90 mm.
2.2. Inspection using the senses
Firstly it is possible to get an indicator of the amount
of clay contained in the soil be simply looking at
the surface of the earth. If large cracks are found
on the surface there is a good chance that there is
clay present. You can also test the quality of the clay
through touch. If the soil is clayey you will find it
difficult to crumble it in your fingers. Furthermore,
when you mix the clay with a little water if the soil is
clayey it will stick to your hand and leave a stain.
2.3. Improving the quality of clay
In order to improve the quality of clay it is good
to introduce additives. These additives fall into 3
categories: other clays, organic materials and sands.
The potteries association in Gemayer uses a red clay
additive which they bring from a nearby hill. The
additive most used by the potteries association in Al
Fashir is donkey dung, although millet and sorghum
chaff as well as sawdust are also used. They are
believed to control shrinkage and cracking during
the drying process and of course these materials are
cheap. The higher the shrinkage rate the more organic
material is needed. However, it is important to note