Left: G1916Q transparent fired at cone 03 over a black engobe (L3685T plus stain) and a kaolin-based low fire stoneware (L3685T). The micro-bubbles are proliferating when the glaze is too thick. Right: A commercial low fire transparent (two coats lower and 3 coats upper). A crystal clear glaze result is needed and it appears that the body is generating gases that cause this problem. Likely the kaolin is the guilty material, the recipe contains almost 50%. Kaolin has a 12% LOI. To cut this LOI it will be necessary to replace some or all of the kaolin with a low carbon ball clay. This will mean a loss in whiteness. Another solution would be diluting the kaolin with feldspar and adding more bentonite to make up for lost plasticity.
G1916Q - Low Fire Frit 3195 Glossy Transparent
An expansion-adjustable cone 04-02 transparent glaze made using three common Ferro frits (low and high expansion) and a suspension strategy that produces an easy-to-use slurry.
L3685U - Cone 03 White Stoneware/Engobe
A white burning body with enough added frit to produce a cone 03 stoneware or white slip for use on a matching red stoneware.
|Temperatures||Body decomposition causes glaze bubbles (1950F-2050F)|
Suspended micro-bubbles in ceramic glazes affect their transparency and depth. Sometimes they add to to aesthetics. Often not. What causes them and what to do to remove them.
Firing: What Happens to Ceramic Ware in a Firing Kiln
Understanding more about changes are taking place in the ware at each stage of a firing and you can tune the curve and atmosphere to produce better ware