It contains significant Frit P-25, I googled that to Digitalfire, it contains 1.8% fluorine! When that gases off during firing are you really equipped to deal with fluorine gas in your studio? One answer is to substitute my own frits (which of course do not contain fluorine). I did the calculations in my account at insight-live.com (see the recipes side-by-side). In the formula, I substituted the F (fluorine) for a mix of CaO/MgO. In the recipe, I substituted Ferro Frit 3110 (it is also a high-sodium frit) for the P-25, then I juggled the rest of the recipe to match up the oxides. More Gerstley Borate supplies the lost B2O3, more ball clay supplies the lost Al2O3 and less silica is needed (because the ball clay brought along more). I ended up with a recipe that is going to suspend much better (more clay) and was able to eliminate the whiting (because the rest of the new recipe is supplying more CaO). This recipe has a high thermal expansion, that means crazing. Would it not be easier to simply add a red stain to a clear glaze you already have that is working well on your clay bodies?
Fluorine at Wikipedia
Specific oxides needed in ceramic glazes can be subject to vaporization (and therefore lost up the chimney of the kiln) if firing proceeds to long or too high.