Mass-Spectrometic Investigations of the Influence of the Firing Atmosphere on Bubble Formation in Porcelain Glazes.

Study of the effect of water vapor partial pressure in different atmosphneres on blistering of porcelain glazes. The gases produced for different times, at different temperatures and in different atmospheres were analyzed. The water vapor partial pressure in the firing atmosphere causes a drop in the viscosity of the glaze, thus making it easier, particularly for large bubbles, to escape from the glaze; this contributes to smoother glaze surfaces in both oxidizing and inert atmospheres. In a reducing atmosphere the water vapor partial pressure tends to neutralize the reduction of both the glaze and the body constituents. H//2 can diffuse into the glaze and lead to the formation of water vapor bubbles, if large amounts of water are dissolved in the glaze. It is shown that the reaction of O//2 with diffusing H//2 increases the proportion of N//2 in the bubbles. The N//2 originating from felspars had no detectable effect on the bubble formation in porcelain glazes. Nor were there signs of any appreciable chemical solution of N//2 that would lead to bubble formation while the glaze film forms.