Just as Mother Nature is responsible for variations in natural minerals, commercial frit manufacturers can and do release material with variations. Frits are made of recipes that must be dosed, mixed, smelted, quenched and ground - leaving plenty of room for error. Shown here is an example of a combination of improper mixing and inadequate smelting. Frits can be made from soluble and carbonate materials that off-gas during smelting, leaving a glass of zero LOI. But that did not happen here: This melt fluidity test shows a good and faulty batch. The volatiles (as exhibited by the bubbles) were not the only problem, a glaze containing 50% of this had severely inadequate melting. Interestingly, the two-pallet batch showed the best results at the top of the first pallet and the worst at the bottom of the second. Another load of faulty frit received later showed similar bubbling but was alumina-short (turning our production matte glaze glossy).
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.
The Chemistry, Physics and Manufacturing of Glaze Frits
A detailed discussion of the oxides and their purposes, crystallization, phase separation, thermal expansion, solubility, opacity, matteness, batching, melting.
Frits are used in ceramic glazes for a wide range of reasons. They are man-made glass powders of controlled chemistry with many advantages over raw materials.