The porcelain mug on the left is fired to cone 6 with G2926B clear glossy glaze. This recipe only contains 25% boron frit (0.33 molar of B2O3). Yet the mug on the right (the same clay and glaze) is only fired to cone 02 yet the same glaze is already well melted! What does this mean? Industry avoids high boron glazes (they consider 0.33 to be high boron) because this early melting behavior means gases cannot clear before the glaze starts to melt (causing surface defects). For this reason, fast fire glazes melt much later. Yet many middle temperature reactive glazes in use by potters have double the amount of B2O3 that this glaze has!
Fast Fire Glazes
Traditional ceramics made in industry are fired very quickly compared to what potters do. Industry must formulate bodies and glazes that fire in an hour or two.
Borate glazes, those fluxed with the oxide B2O3, are the most common type used in ceramic industry and hobby for low and medium temperatures.
Most ceramic glazes contain B2O3 as the main melter. This oxide is supplied by great variety of frits, thousands of which are available around the world.
|Oxides||B2O3 - Boric Oxide|