After the Under Glaze Decoration and Overglaze application, the wares are second time fired and this is called Glost firing. Since raw lead glazes were used in olden days, to avoid volatility the Saggars are coated with small amount of glaze. This prevents the volatility of lead compounds in the glaze. However raw lead glazes are stopped 100% due to health hazards. The introduction of fritted lead glazes or Borax glazes has made possible the open firing of Glostware with greater setting densities and could eliminate the heavier and expensive Saggars from firing process.
Special setting devices are nowadays used for loading of glazed wares so that better firing can be achieved even with very high loading densities. Setters are made out of either silicon carbide or corderite or fire clay. However the preferred material for Setters are nowadays corderite. Different types of kilns are available for glost firing of earthenware products which uses either gas or oil or electricity. Most advanced automation systems are used in the present day kilns for best control of firing which makes it possible to fire the products with minimum quantity of fuel at a cheaper price.
The firing cycles varies between kiln to kiln and also the density of setting. There are kilns available wherein we can fire the products within 2-3 hours. The ware is loaded on bats or conveyor belts made out of special material. Control of the glost firing is very much important to get a better surface quality product with lesser rejection rates. After glost firing the wares are sorted out and passed to warehouse directly or can be sent for onglaze decoration which is the next stage of process meant for double decoration operation.
