Refractive index variations across glass objects and the influence of annealing

Abstract A study was made of the refractive index (RI) variations in glass objects with particular attention to building and vehicle windscreen glass. Substantial variations were found across the thickness of certain specimens which could be attributed to thermal effects during manufacture. RI variations were largest in thick shop windows or toughened glasses but were also detectable in domestic window panes. The application of laboratory annealing greatly reduced variations in RI with the exception of a bottle glass where chemical inhomogeneities may also have been present.