The effect of changes in the glass structure on the colors and magnetic susceptibilities of iron was studied in glasses made of CaO, B2O3, and Al2O3(cabal glasses). As the number of gaps in the structure increased, an increase in the general absorption and a decrease in magnetic susceptibility was observed and was attributed to ferrous iron in network‐forming positions. Further increase in the number of gaps was accompanied by a general increase in transmission as well as by an increase in magnetic susceptibility. This was attributed to the loosening of the structure around the ferrous iron which could easily escape from the interstices and be oxidized to colorless ferric iron taking network‐forming positions. The intensity of the ferrous band depended on the concentration of the ferrous iron and also was affected by the polarizing power of the neighboring cati