This is a cone 11 oxidation melt flow test. Shown (left to right) are the new shipment of Cornwall Stone 2011, the L3617 calculated equivalent (a recipe, see link), the older Cornwall shipment we have been using and the H&G substitute 2011 (far right, mislabelled on the picture). These do not flow well here, a small frit addition is needed to better compare them. However they have melted enough to see some differences in whiteness and degree of melt. Notice the L3617 is more like the old Cornwall than the new Cornwall is.
In ceramic glazes each oxide generally makes a specific contributions to the melting and freezing behavior of the glaze. However interactions are also important.
L3617A - Synthetic Cornwall Subsitute
Substituting Cornwall Stone
How to create a blend of materials to chemically substitute for another (Cornwall Stone is used as an example).