Also known as Pearl Ash. This is the only material in ceramics that can deliver K2O in the exact amount required without bringing other oxides with it, however it is water soluble. The most common source of K2O in glazes is feldspar and normally all of the oxides that feldspar supplies are also needed in glazes (so it is rare that pure and much more expensive K2O is needed). Sometimes this is used to modify the color in glazes. In the manufacture of frits, pearl ash can be an important source of potassium.