Introduction to Glass Evidence in Forensic Science
Case Study: A803852
Scenario: Police respond to a noise complaint.
Discover a car with fractured glass due to two bullet impacts.
Glass found on suspect's shoe.
Tasks include identifying if the glass matches the windshield, shot order, direction, and speed.
Importance of Investigating Glass
Prevalence: Glass is common in storefronts, cars, and homes.
Breakage: Often broken in criminal activities, making it significant forensic evidence.
Types of Evidence:
Class Evidence: Mass-produced, e.g., bottles, windshields.
Individual Evidence: Unique fragments that can be matched to specific items.
Understanding Glass
Definition: Hard, brittle, amorphous solid with randomly arranged atoms.
Production: Melting silicon dioxide, lime or calcium oxide, and sodium oxide.
Natural Occurrence: Can form in volcanic eruptions or lightning strikes.
Types of Glass
Soda Lime Glass
Common in bottles and windows.
Composed mostly of silicon dioxide and sodium dioxide.
Lead or Crystal Glass
Found in fine art and dining ware.
Contains a significant percentage of lead oxide.
Pyrex or Kimax Glass
Used in cooking and lab glassware.
Contains boron, making it heat-resistant.
Colored Glass
Colored by adding metal oxides, e.g., nickel oxide for yellow.
Manufacturing Methods
Annealed Glass
Slowly cooled, weak and easily breaks into sharp fragments.
Laminated Glass
Multiple panes fused with plastic; used in windshields and aquariums.
Tempered Glass
Subject to extreme temperatures or chemicals; breaks into small chunks.
Bullet-Resistant Glass
Laminated and tempered with multiple layers for flexibility and strength.
Forensic Testing for Glass
Density Test
Determines density specific to glass types using mass and water displacement.
Refractive Index Test
Measures how light changes direction through glass.
Can use immersion methods or look for Becke lines.
Fracture Pattern Analysis
Examines radial and concentric fractures.
Determines impact side and speed of impact.
Ballistic and Other Fractures
Ballistic Fractures: Determine entry and exit holes based on cone shape.
Order of Shots: Determined by radial fractures and stopping points.
Impact Angle: Assessed by fragment scatter patterns.
Heat Fractures: Produces wavy patterns unique to heat exposure.
Collection of Glass Evidence
Documentation: Identify, photograph, and label before moving.
Collection: Gather large fragments, wear gloves, and identify surfaces.
Trace Evidence: Note any additional evidence on or around glass.
Conclusion
Understanding types, manufacturing, and tests for glass helps determine crucial details in forensic investigations, such as type, match, order, direction, and speed of events related to glass evidence.