Two glazes, same chemistry, different materials. The glaze on the left is sourcing CaO from wollastonite, the one on the right from calcium carbonate. Thus the oxide chemistry of the two is the same but the recipe of materials sourcing that chemistry is different. The difference in this GLFL test for melt flow is an expression of how choosing different mineral sources to source an oxide can produce melting patterns that go outside what the chemistry suggests. The difference here is not extreme, but it can be much more. Glaze chemistry is relative, not absolute. It works best when you are changing material amounts, not material types. When you do introduce a very different mineral then you have a different system which has its own relative chemistry.
Glaze chemistry is the study of how the oxide chemistry of glazes relates to the way they fire. It accounts for color, surface, hardness, texturem, melting temperature, thermal expansion, etc.
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.
|Oxides||CaO - Calcium Oxide, Calcia|