Earthenware products are normally fired to a maximum temperature of about 1150oC to 1180oC. Modern firing kilns operate with fully automated firing facilities with all regulating control systems automated. However most of the factories use pyrometers like Bullers Rings or Seger Cones to measure the heat work in individual kiln cars. In ceramics it is not the temperature alone which is important but also the time of the heat work the products went through.
Bullers Rings contraction is measured and the corresponding temperature is calculated based on the contraction it went through. This is done in a special guage. The end of the pointer rests on a scale giving the Bullers Ring number. The harder the firing, the higher the ring number. Pyrometric cones operate by fusion which causes the tip of the cone to bend over. The cones are numbered according to the temperature.
Earthenware products are twice fired. The first firing before glazing is called biscuit firing and the one after glazing is called glost firing. Most of the kiln gas is used as main fuel and in some parts of the world, electricity is used as an alternative fuel. Fossil oils also can be used for firing, however the quality of the products fired in electricity/gas kilns are very much superior.
After firing the wares are sent for brushing where various machines are employed. The brushed ware then goes to the next step in the process.
