Glass population study and discrimination of glass samples using Glass Refractive Index Measurement III and scanning electron microscopy/energy dispersive X-ray spectroscopy
Smoker, Meghan Grace
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Glass is a hard, amorphous, and transparent or translucent substance, and it is examined in forensic science to place a person or object at a scene or with a victim when a crime is committed. Due to its brittle nature when combined with some force, glass is often broken, and is then submitted as a type of trace evidence to a crime laboratory in cases such as hit and runs, breaking and enterings, and homicides. Broken glass is most often obtained from bottles, windows, doors, and automobiles, and can easily be found on the street. Previous published research has examined known samples of glass and compared these samples with their known categories or types of glass. In this current research, a population study was conducted based on the collection and analysis of broken glass with unknown origins in Boston, MA. Glass samples (n=100) were collected from the streets and sidewalks around Boston neighborhoods, and an analytical scheme, constructed by the Boston Police Department Crime Laboratory (Boston, MA, USA), was utilized for every sample. This analytical scheme included physical characteristics, such as color, transparency, thickness, curvature and the observance of UV fluorescence. Further instrumental analysis was performed using the Glass Refractive Index Measurement system (GRIM3®) for the measurement of refractive index and the Scanning Electron Microscope and Energy Dispersive Spectroscopy (SEM/EDS) for elemental composition of each sample. Refractive index varies with glass depending on the manufacturing process and its added components and is defined as the ratio of the speed of light in a vacuum to the speed of light in the substance. Using an SEM/EDS it was possible to qualitatively determine the elemental components in each unknown glass sample. Using this analytical scheme, it may be possible to distinguish every unknown sample of glass from each other using differences in physical, optical, and elemental characteristics. This study showed the differences observed in a population of glass within the city of Boston, which ultimately could help with better statistics for testimony when asked about the significance of determining an inclusion or exclusion with casework samples.