The variation of RI over a non-toughened, float pane of glass and a toughened, float pane of glass was investigated. The two panes of colourless, float glass were cut into 150 5cmx5cm squares. The pre-and post-annealing RI values from three random areas from each square were measured. Bayesian statistical hierarchical modelling of the results showed that for the non-toughened, float glass pane, annealing increased the variability in RI by a factor of 1.20-1.58, with a mean of 1.43 (with 95% probability); and for the toughened, float pane of glass annealing decreased the variability in RI by a factor of 0.63-0.76, with a mean of 0.69 (with 95% probability). These results provide information regarding the expected RI variation over entire panes of both non-toughened and toughened float window glass for both pre-and post-annealing RI measurements.
