The colour of the clay in natural state may vary from grey, tan, red, brown, black and white. The colour denotes the presence of either iron or carbonaceous matter. Most of the clay contains considerable amount of iron and carbonaceous matter. Iron in the form of hematite or iron oxide produces the red colour, in the form of limonite gives out yellow colour and in the form of ferrous will produce greys, greens and blacks.
Most of the clays rich in iron are not suitable for making sanitaryware body. The clay which is white or half white in colour with less iron content is the suitable clay for making sanitaryware body. The degree of plasticity can be tested by a simple method. In this test the clay is made into a plastic mass by mixing with water and a little rope of it about the thickness of a pencil.
To be contd……
