Nowhere near enough
I have found a few glaze recipes and made them. Looked into RO tables and tried messing about with a few numbers to change the glazes. Never been too precise about it. Tried to solve crazing by changing out some high expansion flux for lower expansion with some success. Manipulated the silica/alumina ratio to get a matt glaze.
Have some plans to do a lot more testing soon, once I bisque the test tiles...
Good idea with the opacifiers, I use some tin and zinc in my recipe.