In glasses of the system Na2O-CaO-SiO2-Fe2O3, Fe2+ & Fe3+ ions were found by Mossbauer spectroscopy. In samples melted in oxidising atmosphere, both ions occurred in tetrahedral coordination, whereas they occurred in coordination no. 6 in samples with high iron content & meted under reducing conditions. It is shown that a total iron concentration has a stronger influence on the glass properties than the redox state. Differences in the properties of glasses melted in oxidising & reducing atmosphere, were observed at lower temperatures, while at higher temperatures they are very small. Density, microhardness, transition temperature & thermal expansion coefficient of the glasses studied are affected by the changes in redox equilibrium. One can conclude that after reducing treatment iron ions present in the glass structure play a similar role as a network modifier.
