On the colouration of glass by natural solar and other radiations.

Abstract

It is well known that many samples of colourless glass containing manganese slowly assume a violet tint when exposed to sunlight. This effect is frequently seen in plate-glass windows having a southern aspect; watched from year to year they assume a more and more pronounced amethystine hue. The introduction of manganese into glass is to neutralise the colour caused by the presence of iron. Iron gives the glass a greenish tint, and the addition of manganese binoxide performs the double object of oxidising the green proto-salt of iron to the per-salt, and also of imparting a purple shade which neutralises the green-yellow tint of the silicate of peroxide of iron.