Some Spectrophotometric Investigations on Iron Oxide-Containing Soda-Lime-Silica Glasses.-Part I. The Influence of Concentration and Ferric-Ferrous Dissociation.

JSGT 1942 V26 T272-T295

 The series of soda-lime-silica glasses used previously by Densem and Turner in their study of the equilibrium between ferric and ferrous oxides in glasses has now been investigated spectrophotometrically in respect of the visual region. The parent glass had the composition 75% SiO₂, 10 CaO, 15 Na₂O, and iron oxide, from 0.002 to 12.5% expressed as Fe₂O₃, was progressively introduced. At concentrations below 0.6% of iron oxide a linear relation between absorption and degree of ferric oxide dissociation held approximately true within the range of dissociation of about 13-35%. Extrapolation showed that the ferric iron at low concentrations contributes a greenish-yellow colour, whilst ferrous iron bestows a blue colour on the glass. At high concentrations the ferric iron exercised high absorption, particularly in the blue-violet end, thus resulting in a brown or pale brown colour. This high absorption component is sensitive to heat-treatment. The results provide evidence that in attempts to formulate a theory of the decolourising of glass, deductions based on glasses containing other than small amounts of iron oxide are inadmissible.

T. H. Wang, M.Sc., D.I.C., and Professor W. E. S. Turner