Potash Feldspar

Source: http://ctmpotterssupplies.co.uk/ceramicmaterialsglossary.html

K2O 11.3%, Na2O 3.2%, Al2O3 18.5%, SiO2 65.8% typical For medium and high temperature glazes - if a recipe lists feldspar or felspar it probably means Potash Feldspar. If trying to identify some it is not as white as soda. Glazes with 35%+ feldspar are likely to produce crazing problems, more than 50% will be unbalanced and probably lack adquate glassy formers in the glaze.