In glaze chemistry, oxides are classified in various ways to model their contribution to the fired glaze properties
In glaze chemistry oxides are sometimes classified as basic (RO, R2O group) or acidic (RO2). The greater the proportion of oxygen the more acidic it is. Since SiO2 contains the most oxygen, silica-rich rocks are the most acidic. Feldspars predominate in RO2 and can be considered acidic also. However most people simply refer to the acidics as “glass formers”.