Two transparent glazes applied thickly and fired to cone 03 on a terra cotta body. Right: A commercial bottled clear, I had to paint it on in layers. Left: G1916S almost-zero-raw-clay glaze, a mix of Ferro frit 3195, 3110, calcined kaolin and a small amount of VeeGum T. The bubbles you see on the left are from the gas generated by the body. The ones on the right are from body and glaze. How can so many more bubbles be generated within a glaze? Raw kaolin. Kaolin loses 12% of its weight on firing, that turns to gas. Low temperature glazes melt early, while gassing may still be happening. So to get a crystal clear the raw clay content has to be as low as possible. Obviously, a white burning body made from refined materials would be even better. A good compromise: A red slip (or engobe) over a white burning body, it would generate far less gases because of being much thinner and still exhibit the nice red color.
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.
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.
Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it.