0. Kendall/Hunt Publishing Company
Glass Analysis
Students will learn:
The nature of glass.
How various types of glass are made
Know why different types of fracture patterns occur.
Reconstruct events using fracture patterns and deductive logic.
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1. Kendall/Hunt Publishing Company
Common Types
Soda-lime—used in plate and window glass, glass containers, and electric light bulbs
Soda-lead—fine table ware and art objects
Borosilicate—heat resistant, like Pyrex
Silica—used in chemical ware
Tempered—used in side windows of cars
Laminated—used in the windshield of most cars
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2. How is glass made?
In your assigned group make a poster. Your poster should mostly be pictures (with labels).
Determine how your assigned type of glass is made and illustrate using a visual
Show a picture of an example of your type of glass (light bulb, windshield, etc)
List the components added to the glass.
Be ready to present and explain all terminology.
All group members’ names written on the back.

3. Kendall/Hunt Publishing Company
Groups:
Soda-lime—
Soda-lead—
Borosilicate—
Silica—
Tempered—
Laminated—
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4. Kendall/Hunt Publishing Company
Density
Type of Glass
Density
window
headlight
pyrex
lead glass
porcelain
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5. Kendall/Hunt Publishing Company
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
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6. Kendall/Hunt Publishing Company
How does the manufacturing process and additives affect the physical properties of glass?
On page 17 of your notebook, make a connection between the types of glass/manufacturing methods/composition and our big idea.
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7. Kendall/Hunt Publishing Company
Fracture Patterns
As a bullet penetrates glass, the exit hole is larger than the entrance
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8. Kendall/Hunt Publishing Company
Fracture Patterns
Radial fracture lines radiate out from the origin of the impact; they begin on the opposite side of the force
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Fracture Patterns
Concentric fracture lines are circular lines around the point of impact; they begin on the same side as the force
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10. Kendall/Hunt Publishing Company
Fracture Patterns
3R rule—radial cracks form a right angle on the reverse side of the force.
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11. Kendall/Hunt Publishing Company
Fracture Patterns
3R rule—radial cracks form a right angle on the reverse side of the force.
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12. Kendall/Hunt Publishing Company
Sequencing
A high velocity projectile always leaves a hole wider at the exit side of the glass.
Cracks terminate at intersections with others. This can be used to determine the order that the fractures occurred.
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14. Kendall/Hunt Publishing Company
Chapter 14
Glass as Evidence
Class characteristics; physical and chemical properties such as refractive index, density, color, chemical composition
Individual characteristics; if the fragments can fit together like pieces of a puzzle, the source can be considered unique
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15. Considerations for Collection
The collector must consider that fragments within a questioned sample may have multiple origins. If possible, the collector should attempt an initial separation based on physical properties.
The collector must consider the possibility there may be a physical match to a known sample (e.g., a piece of glass to a fractured vehicle headlamp). When an attempt to make a physical match is made at the site of collection, the collector should take precautions to avoid mixing of the known and questioned samples.
Any glass samples collected should be documented, marked (if necessary), packaged, and labeled.
—Forensic Science Communications
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16. Kendall/Hunt Publishing Company
Collecting the Sample
The glass sample should consist of the largest amount that can be practically collected from each broken object and packaged separately. The sample should be removed from the structure (e.g., window frame, light assembly). The inside and outside surfaces of the known sample should be labeled if a determination of direction of breakage or reconstruction of the pane is desired.
When multiple broken glass sources are identified, it is necessary to sample all sources.
A sample should be collected from various locations throughout the broken portion of the object in order to be as representative as possible.
The sample should be collected with consideration being given to the presence of other types of evidence on that sample (e.g., fibers, blood).
—Forensic Science Communications
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