These attempt to show graphically, on an x-y coordinate system, the fired results of a range of oxide mixtures. These graphs are generally used to help isolate, explain and predict how to achieve a specific result. For example, a graph may display results for a constant amount of flux with varying amounts of SiO2 and Al2O3 (the latter corresponding to the x and y of the graph). Within the graphic notations might explain zones of matteness, glossy, crystallization, etc.
Stull chart showing the SiO2-Al2O3-(0.7CaO+0.3KNaO) system