A cone 6 GLFL test for melt flow to compare two calcium carbonates (they make up 27% of this glaze recipe that was designed to maximize their percentage). Notice the amount of bubbles (due to the high loss on ignition of the material). Different brand-names of the material obviously have slightly different chemistries so they exhibit different flow properties during firing.
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.
A Low Cost Tester of Glaze Melt Fluidity
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.