1. Vocabulary Concentric Fractures Radial Fractures Refractive Index
Becke Line
Density

2. Forensic Analysis of Glass

3. Why is Glass Analysis important?
How was it broken?
Link a suspect to the crime
Fingerprints
Blood

4. Glass Fractures
Concentric
Radial
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5. Glass Fractures Concentric: Radial:
A crack in the glass that forms a rough circle around the point of impact.
Radial:
A crack in the glass that extends outward like the spoke of a wheel from the point at which the glass was struck.

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8. Direction of Penetration
A projectile hole is inevitably wider at the exit side
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9. Direction of Penetration
Radial
Concentric
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10. Stress Marks
The perpendicular edge of stress marks (shaped like arches) always face the surface on which the crack originated.
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11. Successive Penetrations
A fracture always terminates at an existing line of fracture…which bullet hole was made first??
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15. INTERACTIVE
Draw two bullet holes in a glass window…label: Concentric fractures, Radial Fractures, and which hole was shot first.

16. Linking Glass to a Suspect…Glass Comparison
If pieces of class are found on a suspect a CSI can compare that glass to glass found at the crime scene.
It can either link a suspect to the scene of a crime or eliminate them as a suspect.

17. Glass Comparison
Physical Examination
Density
Refractive Index

18. Physical Examination With the human eye, a hand lens, or a microscope:
Color
Edge thickness
Presence of labels or imprints
Reconstructing (like a puzzle)

19. Thickness Thickness of glass is related to its application
Light bulbs will be thinner than window glass
Window glass will be thinner than glass from a front door

20. Density
Glass from the same object (same car window, same home window, etc) will have the same density—regardless of the size of the pieces---
Methods of finding Density of Glass:
Mass/Volume with a graduated cylinder
Floatation Method (uses chemicals that are unsafe in a high school classroom)
Modified Floatation Method (uses density comparison in water, rubbing alcohol)

21. Density
If the densities of the glass on the suspect are different from the glass at the crime scene…then the suspect is eliminated
If the densities of the glass on the suspect match the crime scene glass than further tests can be done to ensure the glass is a match.

22. Refractive Index
Any object that transmits light has a refractive index or a measure of how much the object slows the speed of light.
Refractive Index is the ration of the velocity of light in a vacuum to light in the particular medium.
Example: Refractive Index of water is light travels 1.33 times faster in a vacuum than it does through water.
When light passes through one medium to another with a different refractive index, the bending of light occurs (pencil example)

24. Refractive Index Every liquid has its own refractive index.
When glass is inserted into a liquid if its refractive index is the same it will seem to ‘disappear’
FBI has a database of 2000 different types of glass and their refractive index.
The BECKE LINE is the halo that appears around a particle in a liquid with a different refractive index.
Comparison of glass—does it have the same refractive index?

27. Refraction of Glass Video Clip
Insert a link for You Tube Video?

28. INTERACTIVE
Make a chart or diagram to summarize the 3 ways to compare and analyze glass fragments.

29. Assessment
Glass Analysis Lab
Foldable of some kind??