Raw materials often have a specific melting temperature (or they melt quickly over a narrow temperature range). We can use the GLFL test to demonstrate the development of melt fluidity between a frit and a raw material. On the left we see five flows of boron Ferro Frit 3195, across 200 degrees F. Its melting pattern is slow and continuous: It starts flowing at 1550F (although it began to turn to a glass at 1500F) and is falling off the bottom of the runway by 1750F. The Gerstley Borate (GB), on the other hand, goes from no melting at 1600F to flowing off the bottom by 1625F! But GB has a complex melting pattern, there is more to its story. Notice the flow at 1625F is not transparent, that is because the Ulexite mineral within GB has melted but its Colemanite has not. Later, at 1700F, the Colemanite melts and the glass becomes transparent. Technicians call this melting behaviour "phase transition", that does not happen with the frit.
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.
What Determines a Glaze's Firing Temperature?
The oxides contributed by glaze materials determine its chemistry. The chemistry is the main factor determining melting behaviour. But the particle sizes, shapes and mineralogies also come in to play.
The melting temperature of ceramic glazes is a product of many complex factors. The manner of melting can be a slow softening or a sudden liquifying.
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.
Frit Fusibility Test
|B2O3 - Boric Oxide
Gerstley Borate was a natural source of boron for ceramic glazes. It was plastic and melted clear at 1750F. Now we need to replace it. How?
Ferro Frit 3195
|Common frits begin melting (760-)