The Theory of Decolorising with Selenium

JSGT_1937_V21_T087_T094

In selenium decolorising the presence of the compound FeSe is an important factor. The compound forms on cooling glasses containing iron oxide and selenium, the more rapidly the more reducing the melting conditions. Glasses of finest colourless appearance are produced under strongly oxidising melting conditions but are prone to the development of objectionable colours on annealing. Hence, as a compromise, weakly oxidising conditions are employed, and the yellow or brownish tint usually resulting from the use of selenium alone is neutralised by the introduction of a small amount of cobalt oxide to give a glass of neutral tint.

A. Dietzel