Loose materials - The Ecology of Building Materials - page 137

Table 8.5: Examples of pigments used for glazing
ceramics

Colour Alternative pigments Percentage

Yellow Ferric oxide 1-2

Uranium oxide (rare) 4-10

Sodium aranate (rare) 5-15

Potassium aranate (rare) 5-15

Chrome chloride 0.5-1

Antimony trioxide 10-20

Vanadium oxide 2-10

Red Cadmium oxide 1-4

Chrome oxide 1-2

Manganese carbonate 2-4

Green Copper carbonate 1-3

Chrome oxide 1-3

Blue Cobalt carbonate 1-3

Nickel oxide 2-4

can be fired with coal dust, oil vapour or gas, natural gas or bio-gas. The rotating
kiln usually consists of a metal cylinder with a diameter of 2-3 m and a length of
12-60 m. But there are also smaller, molbile models (see Figure 8.13). The tem-
perature in the kiln is about 1150°C and the firing time from clay pellets to
expanded clay pellets is approximately seven minutes.
For the manufacture of a light clay, thermal block Zytan moulds are filled with
light expanded clay, then gases are blown through this mass at temperatures of

Figure 8.13: Section through a Pakistani mobile rotating kiln for the production of expanded
clay. The kiln is about 5 m long with inside diameter of 500 mm. The rate of production is about
125 kg of expanded clay per hour. Source: Asfag 1972