Forensics - glass

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  • Created by: Ashlee
  • Created on: 28-04-15 15:39
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  • Glass
    • properties
      • transparent/translucent materials composed of fused inorganic materials
      • variety of chemical compositions
      • variables in elements alters characteristics and use
    • toughened glass
      • high boron content
      • resistant to thermal shock
      • super heated and rapidly cooled
      • increased bending strength
      • perfect for car windows
    • soda lime glass
      • most common
      • windows; drinks; containers
      • silica; soda & lime
    • probative value
      • evidential potential
      • physical/optical/elemental characteristics
    • analysis
      • macroscopic
        • radial and concentric cracks
        • 3r rule - radial fracture; rear surface; right angles
      • primary and secondary fractures
      • backward fragmentation
      • thickness
      • colour
      • uniformity
      • curvature
      • surface conditions
      • UV light
        • glass fluoresces when use UV light
        • due to float glass manufacture process
        • tin diffuses into glass
    • collection
      • take from window not floor
      • toughened = 50 pebbled
      • sode lime = 6 pieces marked inside and outside
    • refractive index
      • RI = n
      • ratio between speed of light in vacuum and speed of light through medium
      • n = C/v
      • C = speed of light
      • v = velocity thought medium
      • air = 1.0008
      • water = 1.330
      • ice = 1.310
      • glass = 1.510
      • diamond = 2.417
      • ruby = 1.760
      • measured by the emersion method - see if RI is same as oil that surrounds it
    • how it breaks
      • 1) struck
        • 2) bends
          • 3) begins to fracture with radial fracures
            • 4) stress continues - concentric fractures
              • 5) continues with radial and concentric fractures until process stops
    • probative value
      • direction of force
      • type of weapon
      • distribution of glass
      • sequence of events
      • associated evidence - link to victim/suspect/place

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