1. Case Study: Susan Nutt (1987)
At 9:30pm on a cloudy, dark night in February, 19-year-old Craig Elliott Kalani went for a walk in his neighborhood in northwest Oregon but never returned home. A hit-and-run driver killed him. Crime-scene investigators collected pieces of glass embedded in Craig’s jacket and other glass fragments found on the ground near his body.
Police searched for a vehicle that had damages consistent with a hit-and-run accident. They found a car with those types of damages that belonged to a woman named Susan Nutt. In order to connect Ms. Nutt and her car with the crime, the police had to match the glass from the crime scene to the glass in her car. The scientists found that windshield glass from the crime scene contained the same 22 chemical elements as those used to make the glass in Ms. Nutter’s car. The scientists considered both samples of glass to be a definite match.
The glass evidence helped convict Susan Nutt of failure to perform the duties of a driver for an injured person. She was sentenced to up to 5 years in and prison and 5 years’ probation

2. Glass Cartoons

3. Glass: Opening Questions
1. How can glass evidence be useful to forensic science?
2. In what types of crimes or situations may glass evidence be extremely valuable?
3. What type of evidence do you think glass is: class or individual? Explain why.
4. What are some physical or chemical characteristics of glass that could help to distinguish one type of glass from another?
5. When glass breaks, what do the fracture patterns look like? Do they vary depending on the type of glass?

4. GLASS NOTES

5. What Is Glass? Glass is an amorphous solid
 Lacks a rigid, ordered crystal structure of materials
Most common ingredient is quartz sand
Depending on the type or color of glass that is being made, different metal oxides are added

6. Amorphous vs. Crystalline Structure
Amorphous Structure: Glass
Crystalline Structure: Salt (NaCl)

7. Glass Manufacturing It is an automated process
Led to mass production
 Mass production means greater uniformity and less ability to discriminate
Most glass today is called float glass
Made by pouring the molten material onto a bath of melted tin, resulting in a very smooth surface

8. How Float Glass is Made

9. Examples of Float Glass
Crystal Palace railway station, London
Old window in Jena, Germany
Float glass = in upper left section of window
The remaining sections are possibly not float glass as indicated by the distorted reflections of a tree.

10. Glass Manufacturing Tempered glass
Created by subjecting glass to extreme heat then cold, repeated over and over, during the manufacturing process
 Glass breaks into smaller squares rather than into sharp shards
Windshields are specialty glasses made by a having a plastic middle layer that is sandwiched between two layers of glass.
The plastic layer helps hold the glass layers together.

11. Tempered Glass: Shattering Examples
A telephone booth with smashed tempered glass in Holloway, London.

12. Tempered Glass: Car Front Windshields

13. Glass In Forensics
Used in solving automobile accidents, hit-and-runs, burglaries, and assaults
Glass is a type of transfer evidence
Can be individualized and linked to a common source
 Only can individualize a glass fragment, if can fit it like puzzle piece to its source

14. Glass In Forensics
Because of a lack of order and pattern, glass breaks in random patterns
An impact in glass produces two types of fractures
Radial (radiating out from the point of impact)
Concentric (forming circles around the impact)
radial
concentric

15. Radial and Concentric Glass Fractures

16. concentric
radial

17. Direction of Force
 Direction of force can be determined by looking at the cross section of the fractures
The lines created in the glass, called ridges or Wallner lines, show distinctive patterns depending on whether the fractures from which they are collected are concentric or radial

18. Direction of Force
Most reliable determinations are from results closest to the original impact
Perpendicular marks are found on the edge opposite way force was pushing
Remember:
 Radial cracks form Right angles on the Reverse side of the force

19. Direction of Force
Perpendicular marks (~90 degree angles) are found on the edge opposite the way that the force was pushing

20. Projectile Patterns
Small projectiles passing through glass at a high velocity will produce characteristic patterns
 Usually it is a crater with the largest portion on the face of the glass opposite from the impact
Exit hole is larger than entry hole
Lower velocity impacts may not penetrate the glass but leave only a pit or crater on one side of the glass

21. Shattering Due to Heat
The shattering of glass by heat creates a distinctive and different fracture pattern characterized by wavy smooth cracks

22. Order of Impact
If there are many impacts on the same pane of glass, the sequence of events can be deduced from the fracture patterns
 Existing fractures from the 1st impact act as barriers to fractures created by the second impact
Look for abrupt terminations

23. Order of Impact Example
This photo depicts two bullet holes in safety glass. Which hole was created first? How can you tell?
1st
2nd
The hole on the right was created first. Cracks radiating out from the hole will stop when they encounter another crack. Stress placed on the glass (causing it to crack) will be transferred along the existing crack rather than across it.

24. Determining Common Source
Only way to link two fragments of glass to a common source is by the process of physical matching
Each breakage is unique
Creates pieces of a puzzle that the criminalist must place the pieces together

25. Determining Common Source
The criminalist can obtain other information on the glass characteristics
Color
Thickness
Shape
Texture

26. Individual Glass Characteristics
 The two most common physical parameters used to characterize glass samples are the measurements of density and the refractive index

27. Density Density is mass / volume
 Determined by using a floatation technique in which the composition of liquid is varied until the glass sample remain suspended in it

28. Density Type of Glass Density window 2.46-2.49 headlight 2.47-2.63
pyrex
lead glass
porcelain

29. Question
What happens when you look at a key that is placed underwater from above water? Why?

30. Refractive Index
 A quantity that measures the bending of light as it travels from one medium into another
RI = velocity of light in a vacuum
velocity of light in medium
Always will be greater than 1.00
Water has a refractive index of 1.33 (light travels 1.33 times faster in a vacuum than in water)

31. Refractive Index
 The RI depends on the wavelength of light being used and the temperature of the material

32. Refractive Index Measured using a microscope equipped with a hot stage
Glass is immersed in an oily material with a known refractive index
Oil is slowly heated
This changes the refractive index
When glass is not seen in the oil, it has the same refractive index

33. Refractive Index Normal line
Lower RI to Higher RI = Angle bends toward normal line
Higher to Lower RI = Angle bends away from normal line
In air
RI = 1.00
Laser
In glass
RI = 1.50

34. The Becke Line
 The Becke Line is a line that appears as a halo if the refractive indexes of the glass and the material are different
 The Becke Line will disappear when the refractive indexes are the same

35. Becke Lines from Glass Becke line on outside Becke line on inside
RI of glass (1.525) > RI of medium (1.6)
RI of glass (1.525 < RI of medium (1.34)

36. Refractive Index Liquid RI Glass Water 1.333 Vitreous silica 1.458
Olive oil
1.467
Headlight
Glycerin
1.473
Window
Castor oil
1.82
Bottle
Clove oil
1.543
Optical
Bromobenzene
1.560
Quartz
Bromoform
1.597
Lead
Cinnamon oil
1.619
Diamond
2.419

37. Glass Videos 1. Glass Shattering Montage by Jaime Vendura (4:12)
2. Bullet Proof Glass Shooting (0:45)
3. Large Fracture Breaking (3:22)
4. Smashing Glass (1:58)
5. Glass Tables Can Shatter Without Warning (2:26)
6. Glass and Its Importance in Early Science (1:35)
7. Refraction of Light Causes Rod to Appear Bent (0:09)
8. Vanishing Glass Fragment Video (0:27)