Presented paper deals with investigation of selected ternary oxidic system with high content of silicates from the viewpoint of surface properties. Research was focused not only on experimental investigation, but mostly on theoretical modelling of surface tension. This approach was chosen due to absence of compact set of information from the area of heterogeneous processes at high temperatures. It is moreover very often difficult to access appropriate data. Surface properties were investigated by sessile drop method. Afterwards calculation was made with use of selected semi-empirical models and obtained outputs were confronted with experimentally obtained data. Modelling comprised also temperature dependence of surface tension and influence of SiO2 on its values.