Here is what Covia Nepheline Syenite does from cone 3 down to 05

These SHAB fired bars are 95% nepheline syenite (5% Veegum added). By cone 02 (bar marked #4) it is self-glazing and glass-like with a total shrinkage (plastic to fired) of 15% (less than some porcelains). At cone 03 (the #5 bar) the porosity is 3% (a stoneware). These are actually melted more than normal because the Veegum is a flux.