Fluxes are the reason we can fire clay bodies and glazes in common kilns, they make glazes melt and bodies vitrify at lower temperatures.
In ceramic glazes each oxide generally makes a specific contributions to the melting and freezing behavior of the glaze. However interactions are also important.
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 materials of controlled chemistry with many advantages or raw materials.
Feldspar is a natural mineral that, by itself, is the most similar to a high temperature stoneware glaze. Thus it is common to see alot of it in glaze recipes. Actually, too much.
|Oxides||B2O3 - Boric Oxide|
|Oxides||Na2O - Sodium Oxide, Soda|
|Oxides||MgO - Magnesium Oxide, Magnesia|
|Materials||Ferro Frit 3110|