Left: This specimen of VC71 cone 6 matte glaze was felt-marked and cleaned with acetone. A closeup of the ink specks reveals they are held in micro-bubbles breaking at the surface. This specimen has also been thermally stressed in a 300F/ice-water IWCT test (causing the crazing pattern, which curiously, only shows up on part of the surface).
Right: An adjustment to VC71 that adds more boron and Al2O3/SiO2 (while preserving the Si:Al ratio). It is much glossier, confirming that, even though the VC71 matte surface feels functional to the touch, it is a product of improper melting.
Random material mixes that melt well overwhelmingly want to be glossy, creating a matte glaze that is also functional is not an easy task.
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 term used in ceramic to express the degree to which an item is safe and stands up to everyday use. Functionality embodies strength, hardness, resistance to acid attack and thermal shock, etc.