Spectrophotometric Study of Coloured Glasses (1)

Abstract

A systematic study of the colour of glasses containing iron, and both iron and manganese was carried out using the spectrophotometric method.The base glass was a soda-lime-silica type, and the colouring agents added to the batch were rouge, copper slag, manganese dioxide, and manganese ore, all being the technical grade. Twenty four smaples containing different amount of colouring agents were subjected to the investigation. The transmission between 350 and 1100mμ were measured by a photo-electric spectrometer to represent the result by C. I. E. colour specification using mainly the chromaticy coordinates and the lightness which is familiar to glass technologists as luminous transmission.With increasing content of total iron oxide the colour of glasses added with rouge was observed to change from blue to green.If the partial pressure of oxygen is kept constant in the melting processes the relation[FeO]2/[Fe2O3]=k/[O2]1/2=α(constant)would hold, so that the ratio FeO/Fe2O3 is reduced with increasing amount of iron oxide. This means that the yellowish green tint of Fe2O3 would become stronger than the blue tint of FeO.FeO makes the glasses darker nine times as much as Fe2O3, so that a glass containing FeO which is equal to 1/9 of Fe2O3 gives the same luminous transmission.It was confirmed that the luminous transmission is linearly related withe FeO content of glass estimated by direct chemical analysis. This gives the possibility of estimating directly the value of FeO and Fe2O3 with fairly high accuracy by measuring the transmittance at a characteristic wave length. It was proved that this method may be applied to the iron contents of 0.5-2.5wt% Fe2O3.The colour of the glasses added with both iron and manganese changes mainly with the change of the ratio of mangenese to iron. The transmittance curves were classified into three groups, and the authors have advanced the three chemical equations which explain satisf actly the existence of the three types of the transmittance curves.MnO2+3Fe2O3_??_2Fe2O3+2FeO+MnO+O2 (for high iron ratio)2MnO2+2Fe2O3_??_2Fe2O3+2MnO+O2 (for medium iron ratio)3MnO2+Fe2O3_??_Fe2O3+Mn2O3+MnO+O2 (for low iron ratio)