Basicity is a useful concept in metal processing inspite of its uncertain theoretical basis. The unlimited application of basicity in metallurgical systems, however, results in confusion of the basicity concept.
After a short review on the basicity of metallurgical slags was done in the present study, optical basicities in some pure oxides and two phase glases in alkaline borate systems measured by the photoacoustic spectroscopy are reported. Two optical basicity values were obtained in the two phase regions of the borate glasses. It is suggested that basicity can not work usefully in such extreme composition regions and that limitations in basicity should be considered in its metallurgical application.