Lecture 9: Physical Evidence III (Paint) Flashcards

1
Q

What is paint?

A

A liquid spread over rigid surfaces to form a thin, hard coating

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2
Q

What does paint dry into?

A

A hard film consisting of pigments and additives suspended in the binder

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3
Q

In what manner is paint usually applied?

A

In a series of layers

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4
Q

What is the significance of the PDQ database?

A

It is an automobile paint comparison database

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5
Q

What common situation results in paint evidence submitted to a lab?

A

Hit-and-run cases involving automobiles

Collect victim vehicle, paint transfer, suspected source

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6
Q

What are the three types of paint analysis mentioned?

A
  • Microscopic comparison (layers, primer, coatings, scratches, damage)
  • Infrared spectroscopy
  • Pyrolysis gas chromatography
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7
Q

What does a stereoscopic microscope compare in paint analysis?

A

Color, surface texture, and color layer sequence

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8
Q

What is the value of soil as evidence based on?

A

Its prevalence at crime scenes and transferability between the scene and the criminal

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9
Q

What is the first step in soil sample collection?

A

Sampling vertically and horizontally

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10
Q

What is a common practice in soil lab examination?

A

Visual comparison of color and texture under a microscope

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11
Q

What is the purpose of density-gradient tubes in soil analysis?

A

To compare soils based on their density

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12
Q

What is glass?

A

An amorphous fusion of mineral compounds that produces a transparent solid when cooled

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13
Q

What are the physical properties of glass?

A

Hard, elastic, brittle, insulative (thermal and electrical)

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14
Q

What are the chemical properties of glass?

A

Resistant to all but fluorine and very strong bases

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15
Q

What is soda-lime glass commonly used for?

A

Windowpanes and containers

Has sodium oxide (Na2O) to reduce M.P., and quicklime (CaO) to increase durability

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16
Q

What is borosilicate glass commonly used for?

A

Cockware, laboratory glassware, light bulbs

Lime replaced with boron oxide (B2O3) to increase resistance to thermal shock

17
Q

What is lead glass?

A

Known as crystal for decorative glassware, radiation protection

Lime replaced with lead oxide (PbO) to increase refractive index and reduce M.P. & viscosity

18
Q

What does laminated glass consist of?

A

Two sheets of glass with plastic between them

Used in windshield and skylights

19
Q

What makes tempered glass stronger?

A

It is treated by heating and quickly cooling or chemically treating the surface, replacing Na+ with K+

20
Q

What are the six types of glass classified based on composition?

A
  • Soda-lime
  • Borosilicate
  • Lead (crystal)
  • Flat
  • Laminated
  • Tempered
21
Q

How do glass windows break?

A
  • Radial cracks form first
  • Propagated in short segments on opposite side of force
  • Concentric cracks
22
Q

What does the 3R rule in glass fractures state?

A

Radial cracks form at
Right angles on the
Reverse side of the force

23
Q

What are Wallner lines?

A
  • “Stress” marks on edges of broken pieces of glass
  • Perpendicular to unloaded side and parallel to loaded side
24
Q

What are the three exceptions to the three R rule?

A
  • Tempered glass (dices without forming ridges)
  • Small windows held tightly in frame (cannot bend or bulge)
  • Windows broken by heat or explosion (no “point of impact”)
25
26
What indicates the direction of a bullet's impact on glass?
The exit side is wider than the entry side
27
What is the goal of forensic examination of glass?
To determine types of glass, how it was fractured, and individualize it to a source
28
What method is used to determine the refractive index of glass?
Submersion method in liquids of known refractive indexes
29
What is the formula for calculating density?
π = m/V
30
What is the significance of measuring the refractive index?
It can be measured very precisely and is nondestructive
31
What happens to light when it moves from air into water?
Its speed slows and bends light toward the normal line
32
What are Becke lines used for in glass analysis?
To indicate differences in refractive index between glass and surrounding liquid E.g. white line inside means higher refractive index, white line outside means lower refractive index
33
Fill in the blank: Most paint evidence submitted to a lab comes from _______ cases.
hit-and-run
34
True or False: The sequence of impacts on glass can be determined based on crack propagation.
True