The examination of glass particles using the interference objective. Part 2: A survey of flat and curved surfaces

The microscopical examination of original surfaces on casework sized glass particles using an interference objective and the interpretation of their interferograms is discussed. To reduce subjectivity, a numerical criterion was devised to assess the curvature of glass particles and this was then applied to a survey of window, container, tableware and vehicle glasses. Objects with curved surfaces produced particles that were distinctly curved while those from surfaces of both modern and old windows were clearly identifiable as flat. Apparently flat surfaces from tableware and containers almost always yielded specimens that were detectably curved. In addition, there was no evidence that a fracture surface would be confused with an original surface from a plain flat glass.In a ‘blind’ trial to assess the interferometric routines, three examiners correctly identified flat and curved surfaces on 15 particles derived from a selection of glass objects.