Each glaze recipe is followed by an analysis of its Alumina and Silica molecular ratios with respect to one another, and to one net molecule of flux. These ratios can be plotted on the chart of Stull and Howat (below) to see how Alumina and Silica affect the glaze surface. While Stull and Howat is based on specific fluxes (K2O at 0.3 molecules & CaO at 0.7 molecules), altering the concentration of Alumina or Silica in any glaze in similar directions will drive the glaze toward similar boundaries.
As an example from the chart: the best, brightest, gloss glazes have a ratio of 3.8 molecules of silica to 0.57 molecules of Alumina to 1.0 net molecule of flux. Altering that glaze to 2.3 molecules of silica changes the surface from gloss to matt.
Each glaze is also catagorized by predominant flux, for example: Alkaline Earth.