Rushton, Kary2010-03-152010-03-152009https://hdl.handle.net/2292/5703The first part of this research involved the development and validation of a simplified technique for the measurement of the refractive index (RI) before and after the annealing of glass fragments. The technique involved using two different glass fragments crushed from the same piece of glass for the pre and post-annealing RI measurements. Validation of the proposed technique showed that it could be used for further RI analysis on large panes of glass, but would need more rigorous testing before being used for casework samples. The inter- and intra-sample variation of RI over a toughened and non-toughened pane of glass was investigated. The two panes of colourless float glass were cut into 150 5cm x 5cm squares. Three random areas from each of the 150 squares were then measured for pre and post-annealing RI. Results from the variation analysis showed that the float glass pane had a pre-annealing RI range of 0.00016 and a !RI range of 29 x10-5. The toughened glass pane had a pre-annealing RI range of 0.00032 and a !RI range of 39 x10-5. These results provide information regarding the expected RI variation over whole panes of both toughened and non-toughened float window glass. During the RI variation analysis, minimum edge counts were also noted for each pre and post-annealing RI measurement. When plotted against their respective minimum edge counts, RI measurements increased in variability as the edge count values fell below 30. These results suggest that glass fragment edge morphology has a great effect on the subsequent RI measurement made by the GRIM instrument and that ‘poor’ glass fragment edges will give poor or highly variable RI measurements. Due to different manufacturing and cooling regimes for different thicknesses of glass, it is thought that different thicknesses of glass or even different layers of very thick glass would have different !RI values. In order to investigate this, six panes of glass were examined. These panes of glass were 18.29mm, 14.60mm, 11.89mm, 9.78mm, 4.81mm and 3.84mm thick. Three random areas from each pane of glass were measured to determine the average pre-annealing and !RI values for each pane. When glass pane thickness was plotted against !RI, linear regression analysis for the data gives an R2 value of 0.5971, meaning that 59.71% of the variation of the !RI data could be explained by glass thickness. Possible !RI variations across the thickness of a glass pane were investigated by dividing each of the six different thickness panes of glass into either three or five layers. The !RI for each layer was measured. Statistical analysis of these results indicated that there were no observable differences in !RI between the different layers of glass in any of the individual panes. The effect that annealing has on the RI variation within and between glass fragment samples was also analysed in order to determine if the annealing process could aid in further discrimination of glass samples with similar pre-annealing RI measurements. Results showed that a small number of survey glass samples with similar preannealing RI measurements could be discriminated using !RI. However, most samples could not be further discriminated by their !RI values. Overall, especially in reference to casework glass samples, !RI does not appear to provide any significant additional discriminatory information other than to classify a glass fragment as toughened or non-toughened.enItems in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmForensicGlassRefractive IndexAnnealingThesisCopyright: The authorQ112882299